Rapid NeoPixel updates cause apparent hang on ESP32-S3

[einglis]

Board

Lolin S3 mini

Device Description

Bare Lolin S3 mini board. Nothing attached but USB and a serial monitor.

Hardware Configuration

FTDI cable attached to TX (43), RX (44), and Ground.

Version

v2.0.13

IDE Name

Arduino IDE (also seen with PlatformIO)

Operating System

N/A (but actually Linux Mate)

Flash frequency

240 MHz

PSRAM enabled

Unsure

Upload speed

921600

Description

I have a sketch that blinks a status LED at a rate of 10 Hz (from a Ticker). If the CPU gets busy, the updates get bunched together in a burst and the system locks up. This lock up has not been seen on boards with a conventional status LED.
I've replicated this with the example provided. If the digitalWrite in the second loop is commented out, the program continues and the status LED blinks forever. The same effect is seen with the neopixelWrite variant.

Sketch

void setup() 
{
  Serial.begin(115200);
  Serial.println("");
  Serial.println("");
}

void loop() 
{
  Serial.println("blink slow");
  for (auto i = 0; i < 10; i++)
  {
     digitalWrite( LED_BUILTIN, i & 1 );
     //neopixelWrite( 47, i & 1, i & 1, i & 1);  // 47 is Lolin S3 onboard LED
     delay( 100 );
  }
    
  Serial.println("blink fast");
  for (auto i = 0; i < 10; i++)
  {
     digitalWrite( LED_BUILTIN, i & 1 );
     //neopixelWrite( 47, i & 1, i & 1, i & 1);
  }
}

Debug Message

18:25:59.490 -> ESP-ROM:esp32s3-20210327
18:25:59.490 -> Build:Mar 27 2021
18:25:59.490 -> rst:0x1 (POWERON),boot:0x8 (SPI_FAST_FLASH_BOOT)
18:25:59.490 -> SPIWP:0xee
18:25:59.490 -> mode:DIO, clock div:1
18:25:59.490 -> load:0x3fce3808,len:0x44c
18:25:59.490 -> load:0x403c9700,len:0xbd8
18:25:59.490 -> load:0x403cc700,len:0x2a80
18:25:59.490 -> entry 0x403c98d0
18:25:59.755 -> 
18:25:59.755 -> 
18:25:59.755 -> blink slow
18:26:00.748 -> blink fast

Other Steps to Reproduce

No response

I have checked existing issues, online documentation and the Troubleshooting Guide

• I confirm I have checked existing issues, online documentation and Troubleshooting guide.

[einglis]

In fact, we can get even simpler:

  Serial.println("blink fast");
  digitalWrite( LED_BUILTIN, 0 );
  //digitalWrite( LED_BUILTIN, 1 ); // uncomment to cause hang

In case it's of significance: most of the time, the LED stays solid white, but sometimes it goes solid blue.

[SuGlider]

Good news: it works correctly within master (3.0.0).
Bad news: it fails within version/2.x branch. Therefore it fails with v2.0.13.

[SuGlider]

Workaround found! (it may have relationship with the issue ~ IDF | FreeRTOS related?)

void setup() 
{
  Serial.begin(115200);
  Serial.println("");
  Serial.println("");
}

void loop() 
{
  Serial.println("blink slow");
  for (auto i = 0; i < 10; i++)
  {
     digitalWrite( LED_BUILTIN, i & 1 );
     //neopixelWrite( 47, i & 1, i & 1, i & 1);  // 47 is Lolin S3 onboard LED
     delay(100);
  }
    
  Serial.println("blink fast");
  for (auto i = 0; i < 10; i++)
  {
     digitalWrite( LED_BUILTIN, i & 1 );
     delay(1);   // <<<<<<<<<<<<<<<<<<  this delay fixes it.
     //neopixelWrite( 47, i & 1, i & 1, i & 1);
  }
}

[SuGlider]

Root cause found... problem is in the neopixelWrite() function. I'll post a PR for release/2.x branch.

[SuGlider]

@einglis - Please apply the PR #9374 into your development environment and let me know if it fixes this issue.