raspberry pi tft display dsi free sample
CONS: low refresh rate & resolution, supports Raspberry Pi only, requires Raspberry Pi 40PIN GPIO (the SPI bus), poor compatibility with Raspberry Pi system.
PROS: high refresh rate, multiple resolution support, multiple devices support, leaves the Raspberry Pi 40PIN GPIO free, better compatibility with Raspberry Pi system.
Rather than plug your Raspberry Pi into a TV, or connect via SSH (or remote desktop connections via VNC or RDP), you might have opted to purchase a Raspberry Pi touchscreen display.
Straightforward to set up, the touchscreen display has so many possibilities. But if you"ve left yours gathering dust in a drawer, there"s no way you"re going to experience the full benefits of such a useful piece of kit.
The alternative is to get it out of the drawer, hook your touchscreen display to your Raspberry Pi, and reformat the microSD card. It"s time to work on a new project -- one of these ideas should pique your interest.
Let"s start with perhaps the most obvious option. The official Raspberry Pi touchscreen display is seven inches diagonal, making it an ideal size for a photo frame. For the best results, you"ll need a wireless connection (Ethernet cables look unsightly on a mantelpiece) as well as a Raspberry Pi-compatible battery pack.
Several options are available to create a Raspberry Pi photo frame, mostly using Python code. You might opt to script your own, pulling images from a pre-populated directory. Alternatively, take a look at our guide to making your own photo frame with beautiful images and inspiring quotes. It pulls content from two Reddit channels -- images from /r/EarthPorn and quotes from /r/ShowerThoughts -- and mixes them together.
Rather than wait for the 24th century, why not bring the slick user interface found in Star Trek: The Next Generation to your Raspberry Pi today? While you won"t be able to drive a dilithium crystal powered warp drive with it, you can certainly control your smart home.
In the example above, Belkin WeMo switches and a Nest thermostat are manipulated via the Raspberry Pi, touchscreen display, and the InControlHA system with Wemo and Nest plugins. ST:TNG magic comes from an implementation of the Library Computer Access and Retrieval System (LCARS) seen in 1980s/1990s Star Trek. Coder Toby Kurien has developed an LCARS user interface for the Pi that has uses beyond home automation.
Building a carputer has long been the holy grail of technology DIYers, and the Raspberry Pi makes it far more achievable than ever before. But for the carputer to really take shape, it needs a display -- and what better than a touchscreen interface?
Setting up a Raspberry Pi carputer also requires a user interface, suitable power supply, as well as working connections to any additional hardware you employ. (This might include a mobile dongle and GPS for satnav, for instance.)
Now here is a unique use for the Pi and its touchscreen display. A compact, bench-based tool for controlling hardware on your bench (or kitchen or desk), this is a build with several purposes. It"s designed to help you get your home automation projects off the ground, but also includes support for a webcam to help you record your progress.
The idea here is simple. With just a Raspberry Pi, a webcam, and a touchscreen display -- plus a thermal printer -- you can build a versatile photo booth!
Various projects of this kind have sprung up. While the versions displayed above uses a thermal printer outputting a low-res image, you might prefer to employ a standard color photo printer. The wait will be longer, but the results better!
How about a smart mirror for your Raspberry Pi touchscreen display project? This is basically a mirror that not only shows your reflection, but also useful information. For instance, latest news and weather updates.
Naturally, a larger display would deliver the best results, but if you"re looking to get started with a smart mirror project, or develop your own from scratch, a Raspberry Pi combined with a touchscreen display is an excellent place to start.
Many existing projects are underway, and we took the time to compile six of them into a single list for your perusal. Use this as inspiration, a starting point, or just use someone else"s code to build your own information-serving smart mirror.
Want to pump some banging "toons" out of your Raspberry Pi? We"ve looked at some internet radio projects in the past, but adding in a touchscreen display changes things considerably. For a start, it"s a lot easier to find the station you want to listen to!
This example uses a much smaller Adafruit touchscreen display for the Raspberry Pi. You can get suitable results from any compatible touchscreen, however.
Alternatively, you might prefer the option to integrate your Raspberry Pi with your home audio setup. The build outlined below uses RuneAudio, a Bluetooth speaker, and your preferred audio HAT or shield.
Requiring the ProtoCentral HealthyPi HAT (a HAT is an expansion board for the Raspberry Pi) and the Windows-only Atmel software, this project results in a portable device to measure yours (or a patient"s) health.
With probes and electrodes attached, you"ll be able to observe and record thanks to visualization software on the Pi. Whether this is a system that can be adopted by the medical profession remains to be seen. We suspect it could turn out to be very useful in developing nations, or in the heart of infectious outbreaks.
We were impressed by this project over at Hackster.io, but note that there are many alternatives. Often these rely on compact LCD displays rather than the touchscreen solution.
Many home automation systems have been developed for, or ported to, the Raspberry Pi -- enough for their own list. Not all of these feature a touchscreen display, however.
One that does is the Makezine project below, that hooks up a Raspberry Pi running OpenHAB, an open source home automation system that can interface with hundreds of smart home products. Our own guide shows how you can use it to control some smart lighting. OpenHAB comes with several user interfaces. However, if they"re not your cup of tea, an LCARS UI theme is available.
Another great build, and the one we"re finishing on, is a Raspberry Pi-powered tablet computer. The idea is simple: place the Pi, the touchscreen display, and a rechargeable battery pack into a suitable case (more than likely 3D printed). You might opt to change the operating system; Raspbian Jessie with PIXEL (nor the previous desktop) isn"t really suitable as a touch-friendly interface. Happily, there are versions of Android available for the Raspberry Pi.
This LCD display supports Raspbian, Ubuntu MATE, Snappy Ubuntu Core, OSMC, and Windows 10 IOT Core and so on. Please download your system image from raspberry Pi official website: https://www.raspberrypi.org/downloads/
The 5″ LCD display is an LCD display which connects to the Raspberry Pi through the DSI connector. It is capacitive touch LCD. It is a plug-and-play device which doesn’t need install driver. The physical resolution of this LCD display is 800*480.
The touch screen can be used as a mouse device. When we need to input text data to Raspberry Pi board, normally we have to connect a USB keyboard to Pi and this is really inconvenient.
LCD displays have an optimum viewing angle, and depending on how the screen is mounted it may be necessary to change the orientation of the display to give the best results. By default, the Raspberry Pi display and Raspberry Pi are set up to work best when viewed from slightly above, for example on a desktop. If viewing from below, you can physically rotate the display, and then tell the system software to compensate by running the screen upside down.
A number of people have used a Motorola Atrix Lapdock to add a screen and keyboard with trackpad to RasPi, in essence building a RasPi-based laptop computer. Lapdock is a very clever idea: you plug your Atrix smart phone into Lapdock and it gives you an 11.6" 1366 x 768 HDMI monitor with speakers, a keyboard with trackpad, two USB ports, and a large enough battery for roughly 5 hours of use. The smart phone acts as a motherboard with "good enough" performance. The advantage over a separate laptop or desktop computer is that you have one computing device so you don"t need to transfer files between your phone and your desk/laptop.
Unfortunately for Motorola, Lapdock was not successful (probably because of its US$500 list price) and Motorola discontinued it and sold remaining stock at deep discounts, with many units selling for US$50-100. This makes it a very attractive way to add a modest size HDMI screen to RasPi, with a keyboard/trackpad and rechargeable battery power thrown in for free.
Lapdock has two connectors that plug into an Atrix phone: a Micro HDMI D plug for carrying video and sound, and a Micro USB plug for charging the phone and connecting to the Lapdock"s internal USB hub, which talks to the Lapdock keyboard, trackpad, and two USB ports. With suitable cables and adapters, these two plugs can be connected to RasPi"s full-size HDMI connector and one of RasPi"s full-size USB A ports.
The RasPi forum has a long thread on Lapdock with many useful suggestions, photos, and links: I made a Raspberry PI Laptop. There"s also a good "blog entry at element14 with photos and suggestions of where to get cables and adapters: Raspberry Pi Laptop. TechRepublic has a tear-down article with photos of Lapdock internal components here: Cracking Open the Motorola Droid Bionic Lapdock. Paul Mano has a wealth of photos of Lapdock innards at Motorola Atrix Lapdock mod projects.
Lapdock uses the HDMI plug to tell if a phone is plugged in by seeing if the HDMI DDC/CEC ground pin is pulled low. If it"s not, Lapdock is powered off. As soon as you plug in a phone or RasPi, all the grounds short together and Lapdock powers itself on. However, it only does this if the HDMI cable actually connects the DDC/CEC ground line. Many cheap HDMI cables do not include the individual ground lines, and rely on a foil shield connected to the outer shells on both ends. Such a cable will not work with an unmodified Lapdock. There is a detailed "blog entry on the subject at element14: Raspberry Pi Lapdock HDMI cable work-around. The "blog describes a side-benefit of this feature: you can add a small power switch to Lapdock so you can leave RasPi attached all the time without draining the battery.
The Lapdock Micro USB plug is the upstream port of Lapdock"s internal USB hub, and connects to one of RasPi"s full-size USB ports. Lapdock is not USB compliant since it provides upstream power on its Vbus pin. Lapdock uses this to charge the Atrix phone. You can use this feature to power RasPi if you have a newer RasPi. The original RasPi rev 1 has 140 mA polyfuses F1 and F2 to protect the USB ports, which are too small for powering RasPi using upstream power. Newer RasPis replace F1 and F2 with zero Ohm jumpers or eliminate them entirely, which allows Lapdock to provide power. If you don"t mind modifying your original RasPi, you can add shorting jumpers over F1 and F2 or replace them with higher-current fuses.
What gets powered on depends on whether Lapdock is open or closed. If it"s open, the screen and all Lapdock USB ports are powered. If you close Lapdock, the screen and full-size USB ports are powered down, but the Micro USB still provides upstream power. This is for charging an Atrix phone. When you open or close Lapdock, the Micro USB power switches off for about a second so if your RasPi is connected it will reboot and you may have a corrupted file system. There"s discussion about this at the RasPi forum link, and someone has used a supercapacitor to work around the problem: Raspberry Pi lapdock tricks.
When you do not connect a HDMI monitor, the GPU in the PI will simply rescale (http://en.wikipedia.org/wiki/Image_scaling) anything that would have appeared on the HDMI screen to a resolution suitable for the TV standard chosen, (PAL or NTSC) and outputs it as a composite video signal.
The Broadcom BCM2835 only provides HDMI output and composite output. RGB and other signals needed by RGB, S-VIDEO or VGA connectors are however not provided, and the R-PI also isn"t designed to power an unpowered converter box.
Note that any conversion hardware that converts HDMI/DVI-D signals to VGA (or DVI-A) signals may come with either an external PSU, or expects power can be drawn from the HDMI port. In the latter case the device may initially appear to work, but there will be a problem, as the HDMI specs only provide in a maximum of 50mA (@ 5 Volt) from the HDMI port, but all of these adapters try to draw much more, up-to 500mA, in case of the R-PI there is a limit of 200mA that can be drawn safely, as 200mA is the limit for the BAT54 diode (D1) on the board. Any HDMI to VGA adapter without external PSU might work for a time, but then burn out D1, therefore Do not use HDMI converters powered by the HDMI port!
The solution is to either only use externally powered converters, or to replace D1 with a sturdier version, such as the PMEG2010AET, and to replace the power input fuse F3 with a higher rated one, as the current one is only 700mA, and the adapter may use 400mA itself. Also notice that the R-PI"s power supply also must be able to deliver the extra current.
Alternatively, it may be possible to design an expansion board that plugs into the LCD headers on the R.Pi. Here is something similar for Beagleboard:
An additional binary blob might be required for the DSI port to function correctly (or function at all). When or if such a blob will be made available is unknown. Update 04 Jun 2013: "DSI will get done though - there are 1.5M boards out there with the connector on - that would, as you say, have been a waste of money ($120k??) if it never gets used." [1]
The schematics for apples iPhone 3gs and 4g suggest they speak DSI, thus they can probably be connected directly. The older iPhones use a "Mobile Pixel Link" connection from National Semiconductor. The 3GS panel (480×320) goes as low as US $14.88, while the 4G one (960×640, possibly the LG LH350WS1-SD01, with specifications) can be had for US $17.99 or as low as US $14.28. The connectors used might be an issue, but this connector might fit. Additional circuitry might be necessary to provide the display with required 1.8V and 5.7V for operation, and an even higher voltage for the backlight.
The Raspberry Pi provides one clock lane and two data lanes on the S2 connector, as can be read from the schematics. It is currently unknown whether this is enough to drive the iPhone 4G screen, as that screen seems be driven with three data lanes in its original application.
I2C/SPI ADC can be used to interface 4 pin resistive Touch Screens, For example STMPE812A. Texas Instruments has a solution for 4 or 8 wire touchscreens using their rather cheap MSP4309.
Parallel interface displays can be found in many sizes, usually up to 7" and more. Parallel interfaces are usually 8 or 16-bits wide (sometimes 18 or 24-bit wide), plus some control-lines. The Raspberry Pi P1-connector does not contain enough GPIOs for 16-bit wide parallel displays, but this could be solved by borrowing some GPIOs from the CSI-connector or from P5 (on newer Raspberry Pis). Alternatively, some additional electronics (e.g. shift-registers or a CPLD) can be used, which could also improve the framerate or lower the CPU-load.
AdvaBoard RPi1: Raspberry Pi multifunction extension board, incl. an interface and software for 3.2"/5"/7" 16-bit parallel TFT-displays incl. touchscreen with up to 50 frames/s (3.2", 320x240)
Texy"s 2.8" TFT + Touch Shield Board: HY28A-LCDB display with 320 x 240 resolution @ 10 ~ 20fps, 65536 colors, assembled and tested £24 plus postage, mounts on GPIO pins nicely matching Pi board size, or via ribbon cable
A resolution to the test screens that occur during reboot has been released as an app note. The app note can be found in the documents section of the product page here: https://www.crystalfontz.com/product/cfam800480b0050tc-800x480-raspberry-pi-dsi-tft-lcd
*For applications where the controller will be shut down or reset, an additional connection to the reset (RST) pin on the J3 header is required, and must be toggled during boot-up.
**Some versions of Raspbian the creators have inverted the display which can cause the touch screen to not track the same with the image. To fix this, add lcd_rotate = 2 to the config.txt
In these videos, the SPI (GPIO) bus is referred to being the bottleneck. SPI based displays update over a serial data bus, transmitting one bit per clock cycle on the bus. A 320x240x16bpp display hence requires a SPI bus clock rate of 73.728MHz to achieve a full 60fps refresh frequency. Not many SPI LCD controllers can communicate this fast in practice, but are constrained to e.g. a 16-50MHz SPI bus clock speed, capping the maximum update rate significantly. Can we do anything about this?
The fbcp-ili9341 project started out as a display driver for the Adafruit 2.8" 320x240 TFT w/ Touch screen for Raspberry Pi display that utilizes the ILI9341 controller. On that display, fbcp-ili9341 can achieve a 60fps update rate, depending on the content that is being displayed. Check out these videos for examples of the driver in action:
Given that the SPI bus can be so constrained on bandwidth, how come fbcp-ili9341 seems to be able to update at up to 60fps? The way this is achieved is by what could be called adaptive display stream updates. Instead of uploading each pixel at each display refresh cycle, only the actually changed pixels on screen are submitted to the display. This is doable because the ILI9341 controller, as many other popular controllers, have communication interface functions that allow specifying partial screen updates, down to subrectangles or even individual pixel levels. This allows beating the bandwidth limit: for example in Quake, even though it is a fast pacing game, on average only about 46% of all pixels on screen change each rendered frame. Some parts, such as the UI stay practically constant across multiple frames.
A hybrid of both Polled Mode SPI and DMA based transfers are utilized. Long sequential transfer bursts are performed using DMA, and when DMA would have too much latency, Polled Mode SPI is applied instead.
Undocumented BCM2835 features are used to squeeze out maximum bandwidth: SPI CDIV is driven at even numbers (and not just powers of two), and the SPI DLEN register is forced in non-DMA mode to avoid an idle 9th clock cycle for each transferred byte.
Good old interlacing is added into the mix: if the amount of pixels that needs updating is detected to be too much that the SPI bus cannot handle it, the driver adaptively resorts to doing an interlaced update, uploading even and odd scanlines at subsequent frames. Once the number of pending pixels to write returns to manageable amounts, progressive updating is resumed. This effectively doubles the maximum display update rate. (If you do not like the visual appearance that interlacing causes, it is easy to disable this by uncommenting the line #define NO_INTERLACING in file config.h)
A number of other micro-optimization techniques are used, such as batch updating rectangular spans of pixels, merging disjoint-but-close spans of pixels on the same scanline, and latching Column and Page End Addresses to bottom-right corner of the display to be able to cut CASET and PASET messages in mid-communication.
The result is that the SPI bus can be kept close to 100% saturation, ~94-97% usual, to maximize the utilization rate of the bus, while only transmitting practically the minimum number of bytes needed to describe each new frame.
although not all boards are actively tested on, so ymmv especially on older boards. (Bug fixes welcome, use https://elinux.org/RPi_HardwareHistory to identify which board you are running on)
This driver does not utilize the notro/fbtft framebuffer driver, so that needs to be disabled if active. That is, if your /boot/config.txt file has lines that look something like dtoverlay=pitft28r, ..., dtoverlay=waveshare32b, ... or dtoverlay=flexfb, ..., those should be removed.
This program neither utilizes the default SPI driver, so a line such as dtparam=spi=on in /boot/config.txt should also be removed so that it will not cause conflicts.
If you have been running existing fbcp driver, make sure to remove that e.g. via a sudo pkill fbcp first (while running in SSH prompt or connected to a HDMI display), these two cannot run at the same time. If /etc/rc.local or /etc/init.d contains an entry to start up fbcp at boot, that directive should be deleted.
When using one of the displays that stack on top of the Pi that are already recognized by fbcp-ili9341, you don"t need to specify the GPIO pin assignments, but fbcp-ili9341 code already has those. Pass one of the following CMake directives for the hats:
-DFREEPLAYTECH_WAVESHARE32B=ON: If you are running on the Freeplay CM3 or Zero device, pass this flag. (this is not a hat, but still a preconfigured pin assignment)
-DPIRATE_AUDIO_ST7789_HAT=ON: If specified, targets a Pirate Audio 240x240, 1.3inch IPS LCD display HAT for Raspberry Pi with ST7789 display controller
-DKEDEI_V63_MPI3501=ON: If specified, targets a KeDei 3.5 inch SPI TFTLCD 480*320 16bit/18bit version 6.3 2018/4/9 display with MPI3501 display controller.
If you connected wires directly on the Pi instead of using a Hat from the above list, you will need to use the configuration directives below. In addition to specifying the display, you will also need to tell fbcp-ili9341 which GPIO pins you wired the connections to. To configure the display controller, pass one of:
-DILI9341=ON: If you are running on any other generic ILI9341 display, or on Waveshare32b display that is standalone and not on the FreeplayTech CM3/Zero device, pass this flag.
-DILI9340=ON: If you have a ILI9340 display, pass this directive. ILI9340 and ILI9341 chipsets are very similar, but ILI9340 doesn"t support all of the features on ILI9341 and they will be disabled or downgraded.
-DILI9486L=ON: If you have a ILI9486L display, pass this directive. Note that ILI9486 and ILI9486L are quite different, mutually incompatible controller chips, so be careful here identifying which one you have. (or just try both, should not break if you misidentified)
-DGPIO_TFT_DATA_CONTROL=number: Specifies/overrides which GPIO pin to use for the Data/Control (DC) line on the 4-wire SPI communication. This pin number is specified in BCM pin numbers. If you have a 3-wire SPI display that does not have a Data/Control line, set this value to -1, i.e. -DGPIO_TFT_DATA_CONTROL=-1 to tell fbcp-ili9341 to target 3-wire ("9-bit") SPI communication.
-DGPIO_TFT_RESET_PIN=number: Specifies/overrides which GPIO pin to use for the display Reset line. This pin number is specified in BCM pin numbers. If omitted, it is assumed that the display does not have a Reset pin, and is always on.
-DGPIO_TFT_BACKLIGHT=number: Specifies/overrides which GPIO pin to use for the display backlight line. This pin number is specified in BCM pin numbers. If omitted, it is assumed that the display does not have a GPIO-controlled backlight pin, and is always on. If setting this, also see the #define BACKLIGHT_CONTROL option in config.h.
fbcp-ili9341 always uses the hardware SPI0 port, so the MISO, MOSI, CLK and CE0 pins are always the same and cannot be changed. The MISO pin is actually not used (at the moment at least), so you can just skip connecting that one. If your display is a rogue one that ignores the chip enable line, you can omit connecting that as well, or might also be able to get away by connecting that to ground if you are hard pressed to simplify wiring (depending on the display).
To get good performance out of the displays, you will drive the displays far out above the rated speed specs (the rated specs yield about ~10fps depending on display). Due to this, you will need to explicitly configure the target speed you want to drive the display at, because due to manufacturing variances each display copy reaches a different maximum speed. There is no "default speed" that fbcp-ili9341 would use. Setting the speed is done via the option
-DSPI_BUS_CLOCK_DIVISOR=even_number: Sets the clock divisor number which along with the Pi core_freq= option in /boot/config.txt specifies the overall speed that the display SPI communication bus is driven at. SPI_frequency = core_freq/divisor. SPI_BUS_CLOCK_DIVISOR must be an even number. Default Pi 3B and Zero W core_freq is 400MHz, and generally a value -DSPI_BUS_CLOCK_DIVISOR=6 seems to be the best that a ILI9341 display can do. Try a larger value if the display shows corrupt output, or a smaller value to get higher bandwidth. See ili9341.h and waveshare35b.h for data points on tuning the maximum SPI performance. Safe initial value could be something like -DSPI_BUS_CLOCK_DIVISOR=30.
There are a couple of options to explicitly say which Pi board you want to target. These should be autodetected for you and generally are not needed, but e.g. if you are cross compiling for another Pi board from another system, or want to be explicit, you can try:
-DSINGLE_CORE_BOARD=ON: Pass this option if you are running on a Pi that has only one hardware thread (Pi Model A, Pi Model B, Compute Module 1, Pi Zero/Zero W). If not present, autodetected.
-DARMV8A=ON: Pass this option to specifically optimize for ARMv8-A instruction set (Pi 2B >= rev. 1.2, 3B, 3B+, CM3, CM3 lite, 4B, CM4, Pi400). If not present, autodetected.
-DBACKLIGHT_CONTROL=ON: If set, enables fbcp-ili9341 to control the display backlight in the given backlight pin. The display will go to sleep after a period of inactivity on the screen. If not, backlight is not touched.
-DDISPLAY_CROPPED_INSTEAD_OF_SCALING=ON: If set, and source video frame is larger than the SPI display video resolution, the source video is presented on the SPI display by cropping out parts of it in all directions, instead of scaling to fit.
-DDISPLAY_BREAK_ASPECT_RATIO_WHEN_SCALING=ON: When scaling source video to SPI display, scaling is performed by default following aspect ratio, adding letterboxes/pillarboxes as needed. If this is set, the stretching is performed breaking aspect ratio.
-DDISPLAY_SWAP_BGR=ON: If this option is passed, red and blue color channels are reversed (RGB<->BGR) swap. Some displays have an opposite color panel subpixel layout that the display controller does not automatically account for, so define this if blue and red are mixed up.
-DDISPLAY_INVERT_COLORS=ON: If this option is passed, pixel color value interpretation is reversed (white=0, black=31/63). Default: black=0, white=31/63. Pass this option if the display image looks like a color negative of the actual colors.
-DLOW_BATTERY_PIN=
Here is a full example of what to type to build and run, if you have the Adafruit 2.8" 320x240 TFT w/ Touch screen for Raspberry Pi with ILI9341 controller:
If the above does not work, try specifying -DSPI_BUS_CLOCK_DIVISOR=8 or =10 to make the display run a little slower, or try with -DUSE_DMA_TRANSFERS=OFF to troubleshoot if DMA might be the issue. If you are using another display controller than ILI9341, using a much higher value, like 30 or 40 may be needed. When changing CMake options, you can reissue the CMake directive line without having to reclone or recreate the build directory. However you may need to manually delete file CMakeCache.txt between changing options to avoid CMake remembering old settings.
If the user name of your Raspberry Pi installation is something else than the default pi, change the directory accordingly to point to the user"s home directory. (Use pwd to find out the current directory in terminal)
If the size of the default HDMI output /dev/fb0 framebuffer differs from the resolution of the display, the source video size will by default be rescaled to fit to the size of the SPI display. fbcp-ili9341 will manage setting up this rescaling if needed, and it will be done by the GPU, so performance should not be impacted too much. However if the resolutions do not match, small text will probably appear illegible. The resizing will be done in aspect ratio preserving manner, so if the aspect ratios do not match, either horizontal or vertical black borders will appear on the display. If you do not use the HDMI output at all, it is probably best to configure the HDMI output to match the SPI display size so that rescaling will not be needed. This can be done by setting the following lines in /boot/config.txt:
These lines hint native applications about the default display mode, and let them render to the native resolution of the TFT display. This can however prevent the use of the HDMI connector, if the HDMI connected display does not support such a small resolution. As a compromise, if both HDMI and SPI displays want to be used at the same time, some other compatible resolution such as 640x480 can be used. See Raspberry Pi HDMI documentation for the available options to do this.
The refresh speed of the display is dictated by the clock speed of the SPI bus that the display is connected to. Due to the way the BCM2835 chip on Raspberry Pi works, there does not exist a simple speed=xxx Mhz option that could be set to define the bus speed. Instead, the SPI bus speed is derived from two separate parameters: the core frequency of the BCM2835 SoC in general (core_freq in /boot/config.txt), and the SPI peripheral CDIV (Clock DIVider) setting. Together, the resulting SPI bus speed is then calculated with the formula SPI_speed=core_freq/CDIV.
Adjust the CDIV value by passing the directive -DSPI_BUS_CLOCK_DIVISOR=number in CMake command line. Possible values are even numbers 2, 4, 6, 8, .... Note that since CDIV appears in the denominator in the formula for SPI_speed, smaller values result in higher bus speeds, whereas higher values make the display go slower. Initially when you don"t know how fast your display can run, try starting with a safe high setting, such as -DSPI_BUS_CLOCK_DIVISOR=30, and work your way to smaller numbers to find the maximum speed the display can cope with. See the table at the end of the README for specific observed maximum bus speeds for different displays.
Ensure turbo speed. This is critical for good frame rates. On the Raspberry Pi 3 Model B, the BCM2835 core runs by default at 400MHz (resulting in 400/CDIV MHz SPI speed) if there is enough power provided to the Pi, and if the CPU temperature does not exceed thermal limits. If the CPU is idle, or voltage is low, the BCM2835 core will instead revert to non-turbo 250MHz state, resulting in 250/CDIV MHz SPI speed. This effect of turbo speed on performance is significant, since 400MHz vs non-turbo 250MHz comes out to +60% of more bandwidth. Getting 60fps in Quake, Sonic or Tyrian often requires this turbo frequency, but e.g. NES and C64 emulated games can often reach 60fps even with the stock 250MHz. If for some reason under-voltage protection is kicking in even when enough power should be fed, you can force-enable turbo when low voltage is present by setting the value avoid_warnings=2 in the file /boot/config.txt.
Perhaps a bit counterintuitively, underclock the core. Setting a smaller core frequency than the default turbo 400MHz can enable using a smaller clock divider to get a higher resulting SPI bus speed. For example, if with default core_freq=400 SPI CDIV=8 works (resulting in SPI bus speed 400MHz/8=50MHz), but CDIV=6 does not (400MHz/6=66.67MHz was too much), you can try lowering core_freq=360 and set CDIV=6 to get an effective SPI bus speed of 360MHz/6=60MHz, a middle ground between the two that might perhaps work. Balancing core_freq= and CDIV options allows one to find the maximum SPI bus speed up to the last few kHz that the display controller can tolerate. One can also try the opposite direction and overclock, but that does then of course have all the issues that come along when overclocking. Underclocking does have the drawback that it makes the Pi run slower overall, so this is certainly a tradeoff.
On the other hand, it is desirable to control how much CPU time fbcp-ili9341 is allowed to use. The default build settings are tuned to maximize the display refresh rate at the expense of power consumption on Pi 3B. On Pi Zero, the opposite is done, i.e. by default the driver optimizes for battery saving instead of maximal display update speed. The following options can be controlled to balance between these two:
The main option to control CPU usage vs performance aspect is the option #define ALL_TASKS_SHOULD_DMA in config.h. Enabling this option will greatly reduce CPU usage. If this option is disabled, SPI bus utilization is maximized but CPU usage can be up to 80%-120%. When this option is enabled, CPU usage is generally up to around 15%-30%. Maximal CPU usage occurs when watching a video, or playing a fast moving game. If nothing is changing on the screen, CPU consumption of the driver should go down very close to 0-5%. By default #define ALL_TASKS_SHOULD_DMA is enabled for Pi Zero, but disabled for Pi 3B.
The CMake option -DUSE_DMA_TRANSFERS=ON should always be enabled for good low CPU usage. If DMA transfers are disabled, the driver will run in Polled SPI mode, which generally utilizes a full dedicated single core of CPU time. If DMA transfers are causing issues, try adjusting the DMA send and receive channels to use for SPI communication with -DDMA_TX_CHANNEL=
Enabling #define USE_GPU_VSYNC reduces CPU consumption, but because of raspberrypi/userland#440 can cause stuttering. Disabling #defined USE_GPU_VSYNC produces less stuttering, but because of raspberrypi/userland#440, increases CPU power consumption.
The option #define SELF_SYNCHRONIZE_TO_GPU_VSYNC_PRODUCED_NEW_FRAMES can be used in conjunction with #define USE_GPU_VSYNC to try to find a middle ground between raspberrypi/userland#440 issues - moderate to little stuttering while not trying to consume too much CPU. Try experimenting with enabling or disabling this setting.
If your SPI display bus is able to run really fast in comparison to the size of the display and the amount of content changing on the screen, you can try enabling #define UPDATE_FRAMES_IN_SINGLE_RECTANGULAR_DIFF option in config.h to reduce CPU usage at the expense of increasing the number of bytes sent over the bus. This has been observed to have a big effect on Pi Zero, so is worth checking out especially there.
If the SPI display bus is able to run really really really fast (or you don"t care about frame rate, but just about low CPU usage), you can try enabling #define UPDATE_FRAMES_WITHOUT_DIFFING option in config.h to forgo the adaptive delta diffing option altogether. This will revert to naive full frame updates for absolutely minimum overall CPU usage.
In display.h there is an option #define TARGET_FRAME_RATE
A pleasing aspect of fbcp-ili9341 is that it introduces very little latency overhead: on a 119Hz refreshing ILI9341 display, fbcp-ili9341 gets pixels as response from GPIO input to screen in well less than 16.66 msecs time. I only have a 120fps recording camera, so can"t easily measure delays shorter than that, but rough statistical estimate of slow motion video footage suggests this delay could be as low as 2-3 msecs, dominated by the ~8.4msecs panel refresh rate of the ILI9341.
This does not mean that overall input to display latency in games would be so immediate. Briefly testing a NES emulated game in Retropie suggests a total latency of about 60-80 msecs. This latency is caused by the NES game emulator overhead and extra latency added by Linux, DispmanX and GPU rendering, and GPU framebuffer snapshotting. (If you ran fbcp-ili9341 as a static library bypassing DispmanX and the GPU stack, directly linking your GPIO input and application logic into fbcp-ili9341, you would be able to get down to this few msecs of overall latency, like shown in the above GPIO input video)
Interestingly, fbcp-ili9341 is about ~33msecs faster than a cheap 3.5" KeDei HDMI display. I do not know if this is a result of the KeDei HDMI display specifically introducing extra latency, or if all HDMI displays connected to the Pi would have similar latency overhead. An interesting question is also how SPI would compare with DPI connected displays on the Pi.
Unfortunately a limitation of SPI connected displays is that the VSYNC line signal is not available on the display controllers when they are running in SPI mode, so it is not possible to do vsync locked updates even if the SPI bus bandwidth on the display was fast enough. For example, the 4 ILI9341 displays I have can all be run faster than 75MHz so SPI bus bandwidth-wise all of them would be able to update a full frame in less than a vsync interval, but it is not possible to synchronize the updates to vsync since the display controllers do not report it. (If you do know of a display that does actually expose a vsync clock signal even in SPI mode, you can try implementing support to locking on to it)
You can however choose between two distinct types of tearing artifacts: straight line tearing and diagonal tearing. Whichever looks better is a bit subjective, which is why both options exist. I prefer the straight line tearing artifact, it seems to be less intrusive than the diagonal tearing one. To toggle this, edit the option #define DISPLAY_FLIP_ORIENTATION_IN_SOFTWARE in config.h. When this option is enabled, fbcp-ili9341 produces straight line tearing, and consumes a tiny few % more CPU power. By default Pi 3B builds with straight line tearing, and Pi Zero with the faster diagonal tearing. Check out the video Latency and tearing test #2: GPIO input to display latency in fbcp-ili9341 and tearing modes to see in slow motion videos how these two tearing modes look like.
Another option that is known to affect how the tearing artifact looks like is the internal panel refresh rate. For ILI9341 displays this refresh rate can be adjusted in ili9341.h, and this can be set to range between ILI9341_FRAMERATE_61_HZ and ILI9341_FRAMERATE_119_HZ (default). Slower refresh rates produce less tearing, but have higher input-to-display latency, whereas higher refresh rates will result in the opposite. Again visually the resulting effect is a bit subjective.
To get tearing free updates, you should use a DPI display, or a good quality HDMI display. Beware that cheap small 3.5" HDMI displays such as KeDei do also tear - that is, even if they are controlled via HDMI, they don"t actually seem to implement VSYNC timed internal operation.
Having no vsync is not all bad though, since with the lack of vsync, SPI displays have the opportunity to obtain smoother animation on content that is not updating at 60Hz. It is possible that content on the SPI display will stutter even less than what DPI or HDMI displays on the Pi can currently provide (although I have not been able to test this in detail, except for the KeDei case above).
The main option that affects smoothness of display updates is the #define USE_GPU_VSYNC line in config.h. If this is enabled, then the internal Pi GPU HDMI vsync clock is used to drive frames onto the display. The Pi GPU clock runs at a fixed rate that is independent of the content. This rate can be discovered by running tvservice -s on the Pi console, and is usually 59Hz or 60Hz. If your application renders at this rate, animation will look smooth, but if not, there will be stuttering. For example playing a PAL NES game that updates at 50Hz with HDMI clock set at 60Hz will cause bad microstuttering in video output if #define USE_GPU_VSYNC is enabled.
If USE_GPU_VSYNC is disabled, then a busy spinning GPU frame snapshotting thread is used to drive the updates. This will produce smoother animation in content that does not maintain a fixed 60Hz rate. Especially in OpenTyrian, a game that renders at a fixed 36fps and has slowly scrolling scenery, the stuttering caused by USE_GPU_VSYNC is particularly visible. Running on Pi 3B without USE_GPU_VSYNC enabled produces visually smoother looking scrolling on an Adafruit 2.8" ILI9341 PiTFT set to update at 119Hz, compared to enabling USE_GPU_VSYNC on the same setup. Without USE_GPU_VSYNC, the dedicated frame polling loop thread "finds" the 36Hz update rate of the game, and then pushes pixels to the display at this exact rate. This works nicely since SPI displays disregard vsync - the result is that frames are pushed out to the SPI display immediately as they become available, instead of pulling them at a fixed 60Hz rate like HDMI does.
A drawback is that this kind of polling consumes more CPU time than the vsync option. The extra overhead is around +34% of CPU usage compared to the vsync method. It also requires using a background thread, and because of this, it is not feasible to be used on a single core Pi Zero. If this polling was unnecessary, this mode would also work on a Pi Zero, and without the added +34% CPU overhead on Pi 3B. See the Known Issues section below for more details.
There are two other main options that affect frame delivery timings, #define SELF_SYNCHRONIZE_TO_GPU_VSYNC_PRODUCED_NEW_FRAMES and #define SAVE_BATTERY_BY_PREDICTING_FRAME_ARRIVAL_TIMES. Check out the video fbcp-ili9341 frame delivery smoothness test on Pi 3B and Adafruit ILI9341 at 119Hz for a detailed side by side comparison of these different modes. The conclusions drawn from the four tested scenarios in the video are:
This mode uses the GPU vsync signal, but also aims to find and synchronize to the edge trigger when content is producing frames. This is the default build mode on Pi Zero.
The codebase captures screen framebuffers by snapshotting via the VideoCore vc_dispmanx_snapshot() API, and the obtained pixels are then routed on to the SPI-based display. This kind of polling is performed, since there does not exist an event-based mechanism to get new frames from the GPU as they are produced. The result is inefficient and can easily cause stuttering, since different applications produce frames at different paces. Ideally the code would ask the VideoCore API to receive finished frames in callback notifications immediately after they are rendered, but this kind of functionality does not exist in the current GPU driver stack. In the absence of such event delivery mechanism, the code has to resort to polling snapshots of the display framebuffer using carefully timed heuristics to balance between keeping latency and stuttering low, while not causing excessive power consumption. These heuristics keep continuously guessing the update rate of the animation on screen, and they have been tuned to ensure that CPU usage goes down to 0% when there is no detected activity on screen, but it is certainly not perfect. This GPU limitation is discussed at raspberrypi/userland#440. If you"d like to see fbcp-ili9341 operation reduce latency, stuttering and power consumption, please throw a (kind!) comment or a thumbs up emoji in that bug thread to share that you care about this, and perhaps Raspberry Pi engineers might pick the improvement up on the development roadmap. If this issue is resolved, all of the #define USE_GPU_VSYNC, #define SAVE_BATTERY_BY_PREDICTING_FRAME_ARRIVAL_TIMES and #define SELF_SYNCHRONIZE_TO_GPU_VSYNC_PRODUCED_NEW_FRAMES hacks from the previous section could be deleted from the driver, hopefully leading to a best of all worlds scenario without drawbacks.
Currently if one resizes the video frame size at runtime, this causes DispmanX API to go sideways. See raspberrypi/userland#461 for more information. Best workaround is to set the desired screen resolution in /boot/config.txt and configure all applications to never change that at runtime.
The speed of the SPI bus is linked to the BCM2835 core frequency. This frequency is at 250MHz by default (on e.g. Pi Zero, 3B and 3B+), and under CPU load, the core turbos up to 400MHz. This turboing directly scales up the SPI bus speed by 400/250=+60% as well. Therefore when choosing the SPI CDIV value to use, one has to pick one that works for both idle and turbo clock speeds. Conversely, the BCM core reverts to non-turbo speed when there is only light CPU load active, and this slows down the display, so if an application is graphically intensive but light on CPU, the SPI display bus does not get a chance to run at maximum speeds. A way to work around this is to force the BCM core to always stay in its turbo state with force_turbo=1 option in /boot/config.txt, but this has an unfortunate effect of causing the ARM CPU to always run in turbo speed as well, consuming excessive amounts of power. At the time of writing, there does not yet exist a good solution to have both power saving and good performance. This limitation is being discussed in more detail at raspberrypi/firmware#992.
By default fbcp-ili9341 builds with a statistics overlay enabled. See the video fbcp-ili9341 ported to ILI9486 WaveShare 3.5" (B) SpotPear 320x480 SPI display to find details on what each field means. Build with CMake option -DSTATISTICS=0 to disable displaying the statistics. You can also try building with CMake option -DSTATISTICS=2 to show a more detailed frame delivery timings histogram view, see screenshot and video above.
The fbcp part in the name means framebuffer copy; specifically for the ILI9341 controller. fbcp-ili9341 is not actually a framebuffer copying driver, it does not create a secondary framebuffer that it would copy bytes across to from the primary framebuffer. It is also no longer a driver only for the ILI9341 controller. A more appropriate name might be userland-raspi-spi-display-driver or something like that, but the original name stuck.
Yes, it does, although not quite as well as on Pi 3B. If you"d like it to run better on a Pi Zero, leave a thumbs up at raspberrypi/userland#440 - hard problems are difficult to justify prioritizing unless it is known that many people care about them.
Edit the file config.h and comment out the line #define DISPLAY_OUTPUT_LANDSCAPE. This will make the display output in portrait mode, effectively rotating it by 90 degrees. Note that this only affects the pixel memory reading mode of the display. It is not possible to change the panel scan order to run between landscape and portrait, the SPI displays typically always scan in portrait mode. The result is that it will change the panel vsync tearing mode from "straight line tearing" over to "diagonal tearing" (see the section About Tearing above).
If you do not want to have diagonal tearing, but would prefer straight line tearing, then additionally enable the option #define DISPLAY_FLIP_ORIENTATION_IN_SOFTWARE in config.h. That will restore straight line tearing, but it will also increase overall CPU consumption.
Enable the option #define DISPLAY_ROTATE_180_DEGREES in config.h. This should rotate the SPI display to show up the other way around, while keeping the HDMI connected display orientation unchanged. Another option is to utilize a /boot/config.txt option display_rotate=2, which rotates both the SPI output and the HDMI output.
Note that the setting DISPLAY_ROTATE_180_DEGREES only affects the pixel memory reading mode of the display. It is not possible to flip the panel scan to run inverted by 180 degrees. This means that adjusting these settings will also have effects of changing the visual appearance of the vsync tearing artifact. If you have the ability to mount the display 180 degrees around in your project, it is recommended to do that instead of using the DISPLAY_ROTATE_180_DEGREES option.
Edit the file config.h in a text editor (a command line one such as pico, vim, nano, or SSH map the drive to your host), and find the appropriate line in the file. Add comment lines // in front of that text to disable the option, or remove the // characters to enable it.
I don"t know, I don"t currently have any to test. Perhaps the code does need some model specific configuration, or perhaps it might work out of the box. I only have Pi 3B, Pi 3B+, Pi Zero W and a Pi 3 Compute Module based systems to experiment on. Pi 2 B has been reported to work by users (#17).
If the display controller is one of the currently tested ones (see the list above), and it is wired up to run using 4-line SPI, then it should work. Pay attention to configure the Data/Control GPIO pin number correctly, and also specify the Reset GPIO pin number if the device has one.
If the display controller is not one of the tested ones, it may still work if it is similar to one of the existing ones. For example, ILI9340 and ILI9341 are practically the same controller. You can just try with a specific one to see how it goes.
If fbcp-ili9341 does not support your display controller, you will have to write support for it. fbcp-ili9341 does not have a "generic SPI TFT driver routine" that might work across multiple devices, but needs specific code for each. If you have the spec sheet available, you can ask for advice, but please do not request to add support to a display controller "blind", that is not possible.
Perhaps. This is a more recent experimental feature that may not be as stable, and there are some limitations, but 3-wire ("9-bit") SPI display support is now available. If you have a 3-wire SPI display, i.e. one that does not have a Data/Control (DC) GPIO pin to connect, configure it via CMake with directive -DGPIO_TFT_DATA_CONTROL=-1 to tell fbcp-ili9341 that it should be driving the display with 3-wire protocol.
The performance option ALL_TASKS_SHOULD_DMA is currently not supported, there is an issue with DMA chaining that prevents this from being enabled. As result, CPU usage on 3-wire displays will be slightly higher than on 4-wire displays.
The performance option OFFLOAD_PIXEL_COPY_TO_DMA_CPP is currently not supported. As a result, 3-wire displays may not work that well on single core Pis like Pi Zero.
This has only been tested on my Adafruit SSD1351 128x96 RGB OLED display, which can be soldered to operate in 3-wire SPI mode, so testing has not been particularly extensive.
Displays that have a 16-bit wide command word, such as ILI9486, do not currently work in 3-wire ("17-bit") mode. (But ILI9486L has 8-bit command word, so that does work)
I have done close to everything possible to my displays - cut power in middle of operation, sent random data and command bytes, set their operating voltage commands and clock timings to arbitrary high and low values, tested unspecified and reserved command fields, and driven the displays dozens of MHz faster than they managed to keep up with, and I have not yet done permanent damage to any of my displays or Pis.
Easiest way to do permanent damage is to fail at wiring, e.g. drive 5 volts if your display requires 3.3v, or short a connection, or something similar.
The one thing that fbcp-ili9341 stays clear off is that it does not program the non-volatile memory areas of any of the displays. Therefore a hard power off on a display should clear all performed initialization and reset the display to its initial state at next power on.
Yes, fbcp-ili9341 shows the output of the HDMI display on the SPI screen, and both can be attached at the same time. A HDMI display does not have to be connected however, although fbcp-ili9341 operation will still be affected by whatever HDMI display mode is configured. Check out tvservice -s on the command line to check what the current DispmanX HDMI output mode is.
At the moment fbcp-ili9341 has been developed to only display the contents of the main DispmanX GPU framebuffer over to the SPI display. That is, the SPI display will show the same picture as the HDMI output does. There is no technical restriction that requires this though, so if you know C/C++ well, it should be a manageable project to turn fbcp-ili9341 to operate as an offscreen display library to show a completely separate (non-GPU-accelerated) image than what the main HDMI display outputs. For example you could have two different outputs, e.g. a HUD overlay, a dashboard for network statistics, weather, temps, etc. showing on the SPI while having the main Raspberry Pi desktop on the HDMI.
double check that the display controller is really what you expected. Trying to drive with the display with wrong initialization code usually results in the display not reacting, and the screen stays white,
shut down and physically power off the Pi and the display in between multiple tests. Driving a display with a wrong initialization routine may put it in a bad state that needs a physical power off for it to reset,
if there is a reset pin on the display, make sure to pass it in CMake line. Or alternatively, try driving fbcp-ili9341 without specifying the reset pin,
make sure the display is configured to run 4-wire SPI mode, and not in parallel mode or 3-wire SPI mode. You may need to solder or desolder some connections or set a jumper to configure the specific driving mode. Support for 3-wire SPI displays does exist, but it is more limited and a bit experimental.
This suggests that the power line or the backlight line might not be properly connected. Or if the backlight connects to a GPIO pin on the Pi (and not a voltage pin), then it may be that the pin is not in correct state for the backlight to turn on. Most of the LCD TFT displays I have immediately light up their backlight when they receive power. The Tontec one has a backlight GPIO pin that boots up high but must be pulled low to activate the backlight. OLED displays on the other hand seem to stay all black even after they do get power, while waiting for their initialization to be performed, so for OLEDs it may be normal for nothing to show up on the screen immediately after boot.
If the backlight connects to a GPIO pin, you may need to define -DGPIO_TFT_BACKLIGHT=
fbcp-ili9341 runs a clear screen command at low speed as first thing after init, so if that goes through, it is a good sign. Try increasing -DSPI_BUS_CLOCK_DIVISOR= CMake option to a higher number to see if the display driving rate was too fast. Or try disabling DMA with -DUSE_DMA_TRANSFERS=OFF to see if this might be a DMA conflict.
This suggests same as above, increase SPI bus divisor or troubleshoot disabling DMA. If DMA is detected to be the culprit, try changing up the DMA channels. Double check that /boot/config.txt does not have any dtoverlays regarding other SPI display drivers or touch screen controllers, and that it does NOT have a dtparam=spi=on line in it - fbcp-ili9341 does not use the Linux kernel SPI driver.
Check that the Pi is powered off of a power supply that can keep up with the voltage, and the low voltage icon is not showing up. (remove any avoid_warnings=1/2 directive from /boot/config.txt if that was used to get rid of warnings overlay, to check that voltage is good) It has been observed that if there is not enough power supplied, the display can be the first to starve, while the Pi might keep on running fine. Try removing turbo settings or lowering the clock speed if you have overclocked to verify that the display crash is not power usage related.
Double check the Data/Command (D/C) GPIO pin physically, and in CMake command line. Whenever fbcp-ili9341 refers to pin numbers, they are always specified in BCM pin numbers. Try setting a higher -DSPI_BUS_CLOCK_DIVISOR= value to CMake. Make sure no other fbcp programs or SPI drivers or dtoverlays are enabled.
If the color channels are mixed (red is blue, blue is red, green is green) like shown on the left image, pass the CMake option -DDISPLAY_SWAP_BGR=ON to the build.
If the color intensities look wrong (white is black, black is white, color looks like a negative image) like seen in the middle image, pass the CMake option -DDISPLAY_INVERT_COLORS=ON to the build.
If the colors looks off in some other fashion, it is possible that the display is just being driven at a too high SPI bus speed, in which case try making the display run slower by choosing a higher -DSPI_BUS_CLOCK_DIVISOR= option to CMake. Especially on ILI9486 displays it has been observed that the colors on the display can become distorted if the display is run too fast beyond its maximum capability.
fbcp-ili9341 needs a few megabytes of GPU memory to function if DMA transfers are enabled. The gpu_mem boot config option dictates how much of the Pi"s memory area is allocated to the GPU. By default this is 64MB, which has been observed to not leave enough memory for fbcp-ili9341 if HDMI is run at 1080p. If this error happens, try increasing GPU memory to e.g. 128MB by adding a line gpu_mem=128 in /boot/config.txt.
As the number of supported displays, Raspberry Pi device models, Raspbian/Retropie/Lakka OS versions, accompanied C++ compiler versions and fbcp-ili9341 build options have grown in number, there is a combinatorial explosion of all possible build modes that one can put the codebase through, so it is not easy to keep every possible combo tested all the time. Something may have regressed or gotten outdated. Stay calm, and report a bug.
You can also try looking through the commit history to find changes related to your configuration combo, to see if there"s a mention of a known good commit in time that should work for your case. If you get an odd compiler error on cmake or make lines, those will usually be very easy to fix, as they are most of the time a result of some configurational oversight.
First, make sure the display is a 4-wire SPI and not a 3-wire one. A display is 4-wire SPI if it has a Data/Control (DC) GPIO line that needs connecting. Sometimes the D/C pin is labeled RS (Register Select). Support for 3-wire SPI displays does exist, but it is experimental and not nearly as well tested as 4-wire displays.
Second is the consideration about display speed. Below is a performance chart of the different displays I have tested. Note that these are sample sizes of one, I don"t know how much sample variance there exists. Also I don"t know if it is likely that there exists big differences between displays with same controller from different manufacturers. At least the different ILI9341 displays that I have are all quite consistent on performance, whether they are from Adafruit or WaveShare or from BuyDisplay.com.
In this list, Rated SPI Bus Speed is the maximum clock speed that the display controller is rated to run at. The Obtained Bus Speed column lists the fastest SPI bus speed that was achieved in practice, and the core_freq BCM Core speed and SPI Clock Divider CDIV setting that was used to achieve that rate. Note how most display controllers can generally be driven much faster than what they are officially rated at in their spec sheets.
The Frame Rate column shows the worst case frame rate when full screen updates are being performed. This occurs for example when watching fullscreen video (that is not a flat colored cartoon). Because fbcp-ili9341 only sends over the pixels that have changed, displays such as HX8357D and ILI9486 can still be used to play many games at 60fps. Retro games work especially well.
All the ILI9341 displays work nice and super fast at ~70-80MHz. My WaveShare 3.5" 320x480 ILI9486 display runs really slow compared to its pixel resolution, ~32MHz only. See fbcp-ili9341 ported to ILI9486 WaveShare 3.5" (B) SpotPear 320x480 SPI display for a video of this display in action. Adafruit"s 320x480 3.5" HX8357D PiTFTs is ~64% faster in comparison.
The ILI9486L controller based maithoga display runs a bit faster than ILI9486 WaveShare, 50MHz versus 31.88MHz, i.e. +56.8% bandwidth increase. However fps-wise maithoga reaches only 13.56 vs WaveShare 12.97 fps, because the bandwidth advantage is fully lost in pixel format differences: ILI9486L requires transmitting 24 bits per each pixel (R6G6B6 mode), whereas ILI9486 supports 16 bits per pixel R5G6B5 mode. This is reflected in the above chart refresh rate for the maithoga display (marked with a star).
If manufacturing variances turn out not to be high between copies, and you"d like to have a bigger 320x480 display instead of a 240x320 one, then it is recommended to avoid ILI9486, they indeed are slow.
The KeDei v6.3 display with MPI3501 controller takes the crown of being horrible, in all aspects imaginable. It is able to run at 33.33 MHz, but due to technical design limitations of the display (see #40), effective bus speed is halved, and only about 72% utilization of the remaining bus rate is achieved. DMA cannot be used, so CPU usage will be off the charts. Even though fbcp-ili9341 supports this display, level of support is expected to be poor, because the hardware design is a closed secret without open documentation publicly available from the manufacturer. Stay clear of KeDei or MPI3501 displays.
The Tontec MZ61581 controller based 320x480 3.5" display on the other hand can be driven insanely fast at up to 140MHz! These seem to be quite hard to come by though and they are expensive. Tontec seems to have gone out of business and for example the domain itontec.com from which the supplied instructions sheet asks to download original drivers from is no longer registered. I was able to find one from eBay for testing.
Search around, or ask the manufacturer of the display what the maximum SPI bus speed is for the device. This is the most important aspect to getting good frame rates, but unfortunately most web links never state the SPI speed rating, or they state it ridiculously low like in the spec sheets. Try and buy to see, or ask in some community forums from people who already have a particular display to find out what SPI bus speed it can achieve.
One might think that since Pi Zero is slower than a Pi 3, the SPI bus speed might not matter as much when running on a Pi Zero, but the effect is rather the opposite. To get good framerates on a Pi Zero, it should be paired with a display with as high SPI bus speed capability as possible. This is because the higher the SPI bus speed is, the more autonomously a DMA controller can drive it without CPU intervention. For the same reason, the interlacing technique does not (currently at least) perform well on a Pi Zero, so it is disabled there by default. ILI9341s run well on Pi Zero, ILI9486 on the other hand is quite difficult to combine with a Pi Zero.
Ultimately, it should be noted that parallel displays (DPI) are the proper method for getting fast framerates easily. SPI displays should only be preferred if display form factor is important and a desired product might only exist as SPI and not as DPI, or the number of GPIO pins that are available on the Pi is scarce that sacrificing dozens of pins to RGB data is not feasible.
Displays are generally manufactured to utilize one specific interfacing method, with the exception that some displays have a both I²C and
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