Stuck in a Loading Loop

Here are my updates:

  1. Long loop wait time: I’m using a UHS3, V1 32GB SD card.
    at 50MHz clock I get
Running DD WRITE test...
536870912 bytes (537 MB, 512 MiB) copied, 41.4046 s, 13.0 MB/s

Running DD READ test...
536870912 bytes (537 MB, 512 MiB) copied, 24.1178 s, 22.3 MB/s

Then I overclocked SD clock to 100MHz with “sd_clock=100.000 MHz” in /boot/config.txt. This has read/write results:

Running DD WRITE test...
536870912 bytes (537 MB, 512 MiB) copied, 39.5661 s, 13.6 MB/s

Running DD READ test...
536870912 bytes (537 MB, 512 MiB) copied, 12.7305 s, 42.2 MB/s

So for now I’ll continue with the sd overclock.

  1. Touchscreen not working.
    I tried many ideas, posted by others who also had touchscreen problems related to TFT 3.5 screens or similar, even so much as to recompile custom dts files. My problems was that the EV_KEY event would only trigger touchdown value 1 on the first touch and never the release, “value 0”
    type 1 (EV_KEY), code 330 (BTN_TOUCH), value 1
    After the first touch no EV_KEY events ever fired again. At this point, I figured the touch overlay of the screen was no good and bought a Waveshare branded screen. The Waveshare screen exhibited the same behavior. I ended up finding these posts:
    Touchscreen not working · Issue #261 · goodtft/LCD-show · GitHub
    LCD35-Show touch screen not working · Issue #53 · waveshare/LCD-show · GitHub

These and many posts implied that these screen’s touch-panel have problems working with newer kernals (buster, bullseye, etc). I tested this theory by using older hestiapi F/W 1.2 and the touch issue was the same.

I started to research the GPIO that is used for the touch interrupt, and on these screens it is GPIO 17.
I used dtoverlay parameters to experiment, and found that if I added the ads7846 overlay and commented out the display overlay the touch screen worked perfectly; this told me the issue was not the hardware.


Going back and forth between the overlays, I found a horrendous hack:

  • Disable tft35a, enable ads7846, then reboot: touch works but no display
  • after the reboot, edit and enable the tft35a and leave the ads7846 enabled, then “reboot”: The touch works and the display works! So, then I powered down, so that I could do a “cold” hardboot; and this just yields the original problem. No touch but display works. So, for about 15 minutes, I worked on trying to do a soft boot hack, involving using an available GPIO to toggle in a way to know if the hardware had hard booted or soft booted. I gave up when I realized the pain of it all.

So, I went back to GPIO 17 and found that if I add a short polling loop against 17 after bootup via a python script then it forces the touch to work.

import RPi.GPIO as GPIO
import time
GPIO.setup(17, GPIO.IN)

i = 0
while i < 10:
  state = GPIO.input(17)
  i += 1

I tried this on both screens and this worked.

So this thread, is done. I have another issue which, I will start a new thread.