RMT transaction on led strip corrupted by WiFi interrupts

[Pixellord]

Greetings,

I am working on a project in which I use RMT of ESP32S3 to transmit data on a LED strip and WiFi for LED configuration. I have observed that some of the LEDs will flicker especially when the number of connected sockets changes in WiFi driver. And the LEDs will be much more stable if WiFi is off.

The LED driver I am using is https://components.espressif.com/compon ... /led_strip (version 2.5.3). So far I have done the following changes and the flickering still exists:
1. DMA is enabled on RMT Tx
2. the freeRToS thread that calls the LED driver (led_strip_new_rmt_device) runs in Core 1.
3. WiFi task is pinned to Core 0 in menuconfig. So do the other application threads in freeRToS.
4. the priority of interrupts in RMT TX is set to level 3. Higher than 3 is not possbile.
5. SPI RAM config: allocate memory of WiFi and LWIP in SPIRAM first. [/list]

I don't understand why the RMT transaction is still corrupted by WiFi driver because the tasks and ISR are supposed to run on different cores. Does anybody have any idea? Thanks!

[ESP_Sprite]

Can you post your code?

[Pixellord]

Configuration of the LED driver

Code: [Select all] [Expand/Collapse]

1. esp_err_t ledSetup()
2. {
3.    
4.     led_strip_config_t strip_config = {
5.         .strip_gpio_num = LED_RMT_TX_GPIO,        
6.         .max_leds = LED_MAX_LENGTH,              
7.         .led_pixel_format = LED_PIXEL_FORMAT_GRB,
8.         .led_model = LED_MODEL_WS2812,            
9.         .flags.invert_out = false,              
10.     };
11.  
12.     led_strip_rmt_config_t rmt_config = {
13.         .clk_src = RMT_CLK_SRC_DEFAULT,    
14.         .resolution_hz = 10 * 1000 * 1000, // 10MHz
15.         .flags.with_dma = true,            
16.     };
17.     ESP_RETURN_ON_ERROR(led_strip_new_rmt_device(&strip_config, &rmt_config, &h_led_strip),
18.                         TAG, "failed to init RMT device");
19.  
20.     return ESP_OK;
21. }

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Thread for LED strip

Code: [Select all] [Expand/Collapse]

1. xTaskCreatePinnedToCore(&mode_init, "mode_thread", 8192, NULL, 24, NULL, 1);

GeSHi © Codebox Plus Extension

Thread for WiFi. I have mdns also running on core 0.

Code: [Select all] [Expand/Collapse]

1. xTaskCreatePinnedToCore(wifi_app_task, "wifi-app", 8192, NULL, 6, NULL, 0);

GeSHi © Codebox Plus Extension

[Pixellord]

ESP_Sprite, do you have any idea?

[dmitrij999]

Do you need to use multiple RMT channels for different LED strips?
As for me, I worked this around by using SPI

[Pixellord]

Hi dmitrij999, thanks for help. I am only using one RMT channel for one strip.
Workaround with SPI would be my last option if i really could not fix it with RMT.

[Bryght-Richard]

I saw this once, but it was 2.4GHz radio transmission was sagging power supply slightly, so then RMT bitstream level was not reaching VIH level for LED strip.

[ESP_Sprite]

That could be it, tbh. If you're using DMA, I'm not sure what else could interrupt the data stream.

[Pixellord]

Thank you for the help. I think I found the cause of my problem. The DMA buffer size for RMT is by default too small in my case. The data frame has to break into several pieces and then extra delay caused by WiFi is then added in between the fragments. I have increased the mem_block_symbols in led_strip_rmt_config_t and then I don't see any unexpected error on LED strip so far.