Drivers for Adafruit PiTFT28 boards (STMPE610 touchscreen and backlight control)

[SteveSpencer]

At the end of last year, I moved house, and last week I finally finished unpacking! I found a couple of Adafruit PiTFT28 boards (which are for the original model B Pi, so not 2x20 headers) which have an ILI9341 TFT, and STMPE610 touchscreen, plus four pushbutton switches on 'spare' GPIOs.
Apparently the touchscreen uses SPI0.1, and in Trixie, shows up an additional GPIO chip, with line#2 controlling the backlight for the display.

Has anyone done any work with this board in Circle (a long shot, I know, as the board is now obsolete)? I think my only recourse is to look at the linux drivers for it (which IIRC, come in two flavours, SPI and I2C, but this is SPI).

It's a neat design because it fits on top of the Pi (and Pimoroni made cases for it like that), and would be useful for the case where an HDMI screen would be too intrusive/large. Unfortunately, I cannot yet figure out how to turn on the backlight, so have no idea what's on the screen .... :(

Incidentally, why does ST7789 have display text functions, and ILI9341 not have them? I have code written for a Pico which I can port to this to provide a reasonable 8x8 font which gives me CP437 support, but was curious as to why the difference? Perhaps a better solution might be to have an additional CILI9341Device which inherits from CCharDevice, and provides equivalent functionality to CST7789Device?

[rsta2]

The class CCharDevice and methods like CST7789Display::DrawText() are obsolete and deprecated now, because you can use any supported display now with the class CTerminalDevice, which has the same function (and more, including selectable fonts) like CCharDevice. This is demonstrated in sample/08- usbkeyboard for example. Please see the sample's README for details. I did not remove CCharDevice so far, because there are apps available, which use it, but newer display drivers like for the ILI9341 did not receive this support any more. So please use CTerminalDevice, another CILI9341Device is not necessary. Unfortunately I don't know about the backlight control of your display. Circle only supports the XPT2046 touch controller so far (beside the official 7" Touchscreen v1).

[SteveSpencer]

Thanks. I confess, I did not read the sample's README (or look too closely at the code, primarily because previously I had only used HDMI screens or none at all. I will refresh my clone of the repository and spend some time going through the various bits of documentation. I imagine that there will have been other changes in the meantime.
As for my issue, the backlight control isn't that well documented, as the hardware is no longer sold (so I guess, no longer supported), but from what I have been able to find out, the STMPE is a GPIO expander. There is an Arduino library available for a different board, so I will probably see if I can first port the STMPE code to Pico and get a driver working there (I already have ILI9341 code in C). My first aim is to be able to turn the backlight on and off so I can see what is on screen, and then I will look at the touchscreen code. If I have any success, I will turn it into a PR.

Now that I have unpacked, I can get back to my 'to do' list, which includes writing Circle support for a DFRobot USB touchscreen (another piece of "obsolete" hardware!) and this module. I have already decided that I never want to move house again, it's too much work.

[rsta2]

😀 You are welcome. Yes, the display architecture has completely changed in Circle Step49. Please see the CHANGELOG.md file or this for more info! It should be much easier now to integrate a new display in a way, that it can be used with most of the Circle samples.

I searched the Linux kernel drivers source for "STMPE610" and found it in the following files:

• drivers/mfd/stmpe-i2c.c
• drivers/mfd/stmpe.c
• drivers/mfd/stmpe-spi.c
• drivers/gpio/gpio-stmpe.c

But the word "backlight" is not in these files. In don't know, if some of these infos is for your display?

[SteveSpencer]

Sadly, no; they appear to be for an Arduino shield, while I have a PiTFT 2.8. There is a DTS file in the linux source tree which tells me that the STMPE610 has a pin connected to the backlight, rather than using one of the Pi GPIOs. No idea why they decided to do it that way, but hey, that's what it is.
I have taken a simple approach - I have trixie loaded onto the Pi which has this hardware attached, and have set up the line in config.txt to load the overlay (pitft28-resistive). This gives me /dev/fb1 which is 320x240 (16 bit rgba 5/11,6/5,5/0,0/0).
I also have event0 which is platform-20204000.spi-cs-1-platform-stmpe-ts-event as expected.
I see GP#7,8 are SPI CE1/0 lines, GPIO#9,#10,#11 are MISO,MOSI,SCLK, while GPIO#25 is DC (for the display data/command line). In addition, there is gpiochip1 with 6 lines (0,1,3,,5 are input) and line 2 is tagged as output "consumer=soc-backlight".
That will be the backlight, I suspect.
If I run lsmod, I can see that stmpe_ts is loaded, as is fbtft and fb_ili9340, along with other stuff relating to backlight management. Trying to set the backlight via /sys/class/* doesn't seem to work, but it's given me somewhere to start looking.

Thanks for the help/advice.

[rsta2]

OK, but I see, you are on the way to solve this. 😉