Enabling RMT/semaphores in complex code can cause analogread to return values 2x too big

[marcmerlin]

As first reported here MartyMacGyver/ESP32-Digital-RGB-LED-Drivers#7
using the RMT neopixel driver causes analogread to return 4096 for 50%-100% and proper values from 0 to 50%.
Sadly if you are sampling data that needs to go in the 50 to 100% range (joystick), it's impossible to get usable data.
If i comment out just these 3 lines of code, then analogread works properly again:
//RMT.conf_ch[RMTCHANNEL].conf1.mem_rd_rst = 1;
//RMT.conf_ch[RMTCHANNEL].conf1.tx_start = 1;
//xSemaphoreTake(ws2812_sem, portMAX_DELAY);

[projectgus]

This feels like it could be a power glitch. Do you still see the bug if you reconfigure RMT to use a different pin which isn't connected to RGB LEDs?

[marcmerlin]

example code showing the failure: marcmerlin/IoTuz@305b9f7
@projectgus sure, I just tried this:

--- a/IoTuz.cpp
+++ b/IoTuz.cpp
@@ -378,7 +378,7 @@ void IoTuz::begin()
     //pixels.setPixelColor(0, 10, 10, 10);
     //pixels.show();
 #else
-    ws2812_init(RGB_LED_PIN, LED_WS2812B);
+    ws2812_init(0, LED_WS2812B);

I still get:
Analogread test before LEDs enabled, returns 1780 or so): 1767
Turning on LEDs
Before colors
After colors
Analogread test after LEDs enabled, returns 3 if RMT is turned on): 3

[marcmerlin]

Hi @projectgus, since this is likely a platform problem (can't tell if it's arduino-esp32 or the chip underneath), is there someone this could get assigned to?
It would be trivial for you to replicate on your own IoTuz I believe

[projectgus]

Are you able to reproduce this on non-IoTuZ hardware?

[marcmerlin]

I will give that a shot since I now have some, and get back to you.

[marcmerlin]

I was able to reproduce on WROVER, but I then updated arduino-esp32 again, and as of
commit 2b075f3
Author: Me No Dev me-no-dev@users.noreply.github.com
Date: Tue Apr 4 02:50:27 2017 +0300
the problem is fixed.
I can now use the RMT neopixel library MartyMacGyver/ESP32-Digital-RGB-LED-Drivers
and analogread now returns proper enough looking values
I'm going to mark this closed, thanks @me-no-dev for the newer arduino-esp32