PiBox

Manufacturer page: https://www.elecrow.com/5-inch-hdmi-800-x-480-capacitive-touch-lcd-display-for-raspberry-pi-pc-sony-ps4.html
Wiki Page: https://www.elecrow.com/wiki/index.php?title=RC050_5_inch_HDMI_800_x_480_Capacitive_Touch_LCD_Display_for_Raspberry_Pi/_PC/_SONY_PS4

config.txt:

hdmi_force_hotplug=1
max_usb_current=1
hdmi_drive=1
hdmi_group=2
hdmi_mode=1
hdmi_mode=87
hdmi_cvt 800 480 60 6 0 0 0
dtoverlay=ads7846,cs=1,penirq=25,penirq_pull=2,-
speed=50000,keep_vref_on=0,swapxy=0,pmax=255,xohms=150,xmin=200,xmax=3900,
ymin=200,ymax=3900
display_rotate=

This config, via the dtoverlay for ads7846, adds an input device and that apparently is supported by the touchscreen library (libpibox).

piboxLoadDisplayConfig[pibox.c:210] INFO Using an LCD/Touchscreen display
loadDisplayConfig[launcher.c:239] INFO Touch screen support enabled.
main[launcher.c:1298] INFO display type: Unknown
main[launcher.c:1305] INFO Registering imageTouch.
piboxTouchRegisterCB[touchProcessor.c:550] INFO Registered a touch ABS callback.
piboxLoadDisplayConfig[pibox.c:172] INFO Width 800 Height 480 (800x480)
piboxLoadDisplayConfig[pibox.c:193] INFO Screen size is SMALL
piboxLoadDisplayConfig[pibox.c:210] INFO Using an LCD/Touchscreen display
setupTouchRegions[touchProcessor.c:86] INFO Width / Height: 800 / 480
setupTouchRegions[touchProcessor.c:102] INFO region x.y: 0 / 0
setupTouchRegions[touchProcessor.c:102] INFO region x.y: 266 / 160
setupTouchRegions[touchProcessor.c:102] INFO region x.y: 532 / 320
piboxTouchStartProcessor[touchProcessor.c:474] INFO Started touchProcessor thread.
ts_setup[touchProcessor.c:170] INFO Have FT5406 memory based driver, want ADS7846 Touchscreen
ts_setup[touchProcessor.c:170] INFO Have ILITEK ILITEK-TP, want ADS7846 Touchscreen
ts_setup[touchProcessor.c:170] INFO Have raspberrypi-ts, want ADS7846 Touchscreen
ts_setup[touchProcessor.c:170] INFO Have ADS7846 Touchscreen, want ADS7846 Touchscreen
ts_setup[touchProcessor.c:173] INFO Using device /dev/input/event3
ts_setup[touchProcessor.c:211] INFO Reading From : ADS7846 Touchscreen (ADS7846 Touchscreen)

So the I need to see if touch events are showing up at all. Maybe it just needs calibration.

This might be a cable problem. The HDMI display has a micro USB port connected to a USB-A connector on an unpowered hub connected to the USB port of the Pi Zero W. This combination might not work. I would need a micro usb to micro usb to test that theory and I don't think I have one.

One way around this might be to allow a config option to override probing. If TSLIB_TSDEVICE is set in the environment then that can be used instead. So a config option of

tsdev=/dev/input/event0

Can be picked up by cli.c which calls setenv(TSLIB_TSDEVICE, path, 1) so that the touchscreen library will use that instead of probing. It's a hack for now. I'd still like to know why the probe finds /dev/input/event1 instead of event0.

I found the problem. Running evtest with no arguments lists the input event devices.

# evtest
No device specified, trying to scan all of /dev/input/event*
Available devices:
/dev/input/event0:    QDtech MPI5001
/dev/input/event1:    ADS7846 Touchscreen

Both are enabled with the ADS7846 driver which is enabled in the config.txt for the elecrow 5in display. However, unlike other ADS7846 devices, this one wants the ODTech MPI5001 device to handle input events.

1. The array is static and can't be easily extended.
2. Forcing order on the array overly complicates it.
3. We can identify which device is running using EDID data and then configure what device name to use from that.

That last item is the kicker - While I can leave the ts_name_default[] array in place (so things that used to work will still work), I can insert the use of a config file that tells me what device name to search for. That makes extending touchscreen.c much simpler and external to the library itself.

Even easier: ts_setup() includes optional use of the environment variable TSLIB_TSDEVICE. So before that choice is made, we call set_env(TSLIB_TSDEVICE, name). This can be done in a new touchscreen.c function called piboxTouchInit() that parses /etc/ts_device.conf, which simply has the name of the device to use. /etc/ts_device.conf is generated by S15Config from the EDID data by sourcing /etc/ts_devices and taking the value of the EDID Device ID (with spaces converted to underscores) variable. So, something like this.

S15Config runs the following command to get the EDID device ID:

/opt/vc/bin/tvservice -n

device_name=MPI-MPITEST

MPI-MPITEST="QDtech MPI5001" 

When an app starts and decides it will be a touchscreen, it currently calls piboxTouchRegister(). This will call, automatically and before anything else, piboxTouchInit() to read /etc/ts_device.conf and use it's value, if any, to set the environment variable TSLIB_TSDEVICE.

1. S15Config must clear /etc/ts_device.conf (zero it out but leave it in place) if no match is found the EDID device id.
2. /etc/ts_devices is manually updated in the dev platform skeleton tree. It can also be updated manually on a running device.

Note that there is a ads7846.dtbo overlay that we're not specifically loading yet. This could go into a /usr/share/pibox/configs/Display-ads7846.txt config and update the functions:optimizeTouchscreen() init script function to handle setup on firstboot.

Both the Elecrow 5" HDMI and the GeeekPi 5" HDMI use the ads7846, so the same display config works with both. However, psplash is not working on either.

The Elecrow model does use the MPI5001 touch processor so the updates to libpibox:touchprocessor.c are still required.

But the bigger problem is automating things. I need a way to know that the display is the Elecrow model. The tvservice --n doesn't seem to work anymore. I can use tvservice --d /tmp/edid.dat to dump the data and then used edid-decode to print it in human readable format. An even simpler way is to use the command edid-decode < /sys/class/drm/card0-eDP-1/edid, but I need to add Target-Packages->Hardware-Handling->edid-decode to the Buildroot config.

In the latter case I need to look for the edid file under /sys/class/drm/*, which should probably be the same all the time on Raspberry Pi though I'm not clear that it is.

Update¶

I searched for the edid file on a RPi3 | RPiLCD but it wasn't there. I then added dtoverlay=vc4-fkms-v3d to the display-config.txt and rebooted - the edid file is now there. However, it's now under /sys/class/drm/card0-DSI-1/edid. I then tried adding that overlay to an RPi 2 v1.1 board with an HDMI output and the edid file showed up at /sys/class/drm/card0-HDMI-A-1/edid. The commonality here is that there is only one edid file uder /sys/class/drm as long as two monitors are not connected.

The code for finding the edid is already in tvservice, so using that command to dump the file first is probably easier than trying to write a find-based command to get the edid file. So I'll use tvservice for non-RPiLCD displays and choose the display-config.txt from the output of edid-decode.

1. /opt/vc/bin/tvservice -d /tmp/edid.dat
2. edid-decode /tmp/edid.dat | grep "Manufacturer" | cut -f2 -d":" | sed 's/ //'
3. edid-decode /tmp/edid.dat | grep "Model" | cut -f2 -d":" | sed 's/ //'

The Manufacturer and Model together can be used to select the display config.txt in functions:touchscreenOptimize().

That's all that's necessary right now since any other HDMI monitors don't need special configuration and the TFT displays are handled separately via the lcdshow package.