kedei 3.5 inch spi tft lcd version 6.3 factory

While googling for any info about lcd controller I came across this page: http://heikki.virekunnas.fi/2015/raspberry-pi-tft/, author managed to get from manufacturer patch file for kernel sources and tested it with 4.1.y - on which lcd worked. But still LCD replace HDMI, but I want to use this screen as additional for user interaction, while the bigger on HDMI as presentation monitor.

Since, fbtft has been merged with rpi kernel, so the fb drivers (including ili9341.c) was moved to fbtft_device driver (so the author of page can"t compile latest kernel with driver+patch).

So something about hardware, which I reverse engineered by the "hard way" - "grab multimeter and run through all LCD FPC pins and shift register pins"

Now I noticed there is "9486L" which can suggest that LCD screen is controlled by ILI9486L, I found this LCD on taobao too but I can"t contact seller.

I"m pretty sure about D/C (Pin 37 on LCD) and Reset (Pin 19 on LCD) pins by looking into driver code, but I can"t identify other signals (WR/RD/CS/etc...)

[ 0.000000] Linux version 3.18.9-v7 (lgh@lgh-ThinkPad-X200) (gcc version 4.7.1 20120402 (prerelease) (crosstool-NG 1.15.2) ) #7 SMP PREEMPT Sun Jun 28 09:33:18 CST 2015

- Controller is not ILI9341/ILI9325 - those are for smaller displays (320x240, etc...), I guess this might be ILI9486/9488 because they are for 480x320 displays. But when I compared init with DS it does not fit right so LCD can have a clone of ILI9486/9488 ...

- Module use only SPI interface and two CE signals (CE0 for touch controller, CE1 for LCD shift registers - compared to others lcd modules, in KeDei module this is swapped),

So I just purchased a KeDei 3.5" TFT Display (v6.3) for my Raspberry Pi 3, and I have found out that the display only works with premade Raspbian / Ubuntu / Kali images. This wouldn"t be a problem, but those modified images don"t seem to work with HDMI. What I want is to be able to use HDMI with my TV/Monitor, and when I take my Pi to go, I"d like to just be able to plug the display into the Pi. I installed the drivers on Raspbian Pixel, when booting up the Pi with the KeDei display after installing the drivers, it just froze on the console. I plugged in an HDMI monitor (while the display was still plugged in) and rebooted my Pi, and it went past the console and booted to the Desktop on the HDMI monitor, but not on the LCD Display.

Thanks for donating the display @Vvvsebastar . Got it now to work, uploaded first working version of code up at a backup branch https://github.com/juj/fbcp-ili9341/tree/kedei_v6_3_mpi3501 - that gets pixels showing on screen, although far from ready.

It looks like according to https://github.com/goodtft/LCD-show the display is a "MPI3501" controller. That is a new one, have not encountered this before. The implementation was done by by sniffing the data bus from the working binary driver.

Something that took two nights of debugging to figure out, is that there is a peculiar interplay of the touch controller and the LCD display in play. The two pieces are not separate, i.e. it is not possible to just initialize the display, but one must initialize both, they communicate internally somehow. Another head scratcher is that the T_CS and L_CS lines have some kind of interaction as well. After sending each 32-bit frame to the LCD display, one must do a dummy "pump" the Chip Select line of the Touch Controller to be enabled for a fraction of a microsecond (with no actual communication taking place), after which the LCD display CS line needs to be disabled likewise for a ~50ns period. That is, one cannot ignore the T_CS line if touch is not in use, but the LCD display is unable to receive/process commands if the Touch Controller is not flipped after each sent 32-bit frame. This hurts bandwidth and CPU usage, and also prevents use of DMA, because it would mean that the DMA controller should write to three data lines simultaneously in a synchronized manner, instead of just pumping bytes out the SPI MOSI bus, something that the DMA controller on the Pi cannot do (without resorting to bit banging). It is not yet certain if pixel color data writes have the same requirement as well, or if this peculiar LCD+Touch pumping is only needed for initialization and/or bus commands though.

Brief speed testing suggests that the controller can reliably handle a 33.333MHz SPI bus speed, but it was not able to do 40MHz. Because of the CS line juggling, effective bus speed remains lower, about 22mbps (22/33 ~ 67% utilization). Tallying up the above protocol framing with -75% / -50% wastage, the effective pixel bandwidth is something around 5.5mbps - 11mbps. The design choices lose around ~66%-85% of the bandwidth they could have had.

I had in plans to create a custom driver but I decided this is not worth my time. I"m going to "re-interface" this lcd to be supported by fbtft. I have a prototype pcb with fbtft-spi interface ready (I have to send this project to pcb prototype service).

Unfortunatly, because of my "spider-circuit" I"ve broken my lcd (I"ve made a some short