ESP32S3 RMT "no free tx channels" opening third channel

[horace99]

using ESP32-S3-DevKitC-1 using ESP-IDE on Windows 10
attempting to generate 1KHz three phase pulses using RMT
ESP32S3 technical reference manual section 37.2 states
• Four TX channels
• Four RX channels
running the following code which attempts to open three Tx channels

Code: [Select all] [Expand/Collapse]

1. #include <stdio.h>
2. #include <stdbool.h>
3. #include <unistd.h>
4. // ESP32S3 RMT 1KHz three phase square wave  sync test
5.  
6.  
7. #include "driver/rmt_tx.h"
8.  
9. void app_main(void)
10. {
11.  
12.  printf("ESP32S3 RMT !KHz three phase sync test\n");
13.   //delay(2000);
14.   // setup Tx channels
15.   rmt_channel_handle_t tx_channels[3] = { NULL };
16.   gpio_num_t tx_gpio_number[3] = { GPIO_NUM_16, GPIO_NUM_17, GPIO_NUM_18 };  // pin numbers
17.   for (int i = 0; i < 3; i++) {
18.     printf("setting up channel %d\n", i);
19.     rmt_tx_channel_config_t tx_chan_config = {
20.       .gpio_num = tx_gpio_number[i],
21.       .clk_src = RMT_CLK_SRC_DEFAULT,
22.       .resolution_hz = 1 * 1000 * 1000,  // 1MHz clock
23.       .mem_block_symbols = 64,
24.       .trans_queue_depth = 1,
25.     };
26.     ESP_ERROR_CHECK(rmt_new_tx_channel(&tx_chan_config, &tx_channels[i]));
27.   }
28.   rmt_transmit_config_t transmitConfig = {
29.     .loop_count = -1
30.   };
31.   rmt_encoder_handle_t copyEncoder =NULL;
32.   rmt_copy_encoder_config_t copyEncoderConfig = {};
33.   assert(rmt_new_copy_encoder(&copyEncoderConfig, &copyEncoder) == ESP_OK && "Failed to Create Copy Encoder");
34.   ESP_ERROR_CHECK(rmt_enable(tx_channels[2]));
35.   ESP_ERROR_CHECK(rmt_enable(tx_channels[1]));
36.   ESP_ERROR_CHECK(rmt_enable(tx_channels[0]));
37.  
38.   // setup sync manage for the three pulses
39.   rmt_sync_manager_handle_t synchro = NULL;
40.   rmt_sync_manager_config_t synchro_config = {
41.     .tx_channel_array = tx_channels,
42.     .array_size = sizeof(tx_channels) / sizeof(tx_channels[0]),
43.   };
44.   ESP_ERROR_CHECK(rmt_new_sync_manager(&synchro_config, &synchro));
45.  
46.   printf("Starting Transmitters\n");
47.   // setup pulse patterns - clock is 1MHz
48.   // two 200KHz pulses 40% duty cycle
49.   const rmt_symbol_word_t pulsePattern1[] = {
50.     { .duration0 = 500, .level0 = 1, .duration1 = 500, .level1 = 0 },
51.   };
52.   const rmt_symbol_word_t pulsePattern2[] = {
53.     { .duration0 = 333, .level0 = 0, .duration1 = 500, .level1 = 1 },
54.     { .duration0 = 100, .level0 = 0, .duration1 = 67, .level1 = 0 },
55.   };
56.     const rmt_symbol_word_t pulsePattern3[] = {
57.     { .duration0 = 167, .level0 = 0, .duration1 = 500, .level1 = 1 },
58.     { .duration0 = 100, .level0 = 0, .duration1 = 233, .level1 = 0 },
59.   };
60.  
61.   assert(rmt_transmit(tx_channels[0], copyEncoder, &pulsePattern1, sizeof(pulsePattern1), &transmitConfig) == ESP_OK && "Failed to begin transmitting");
62.   assert(rmt_transmit(tx_channels[1], copyEncoder, &pulsePattern2, sizeof(pulsePattern2), &transmitConfig) == ESP_OK && "Failed to begin transmitting");
63.   assert(rmt_transmit(tx_channels[2], copyEncoder, &pulsePattern3, sizeof(pulsePattern3), &transmitConfig) == ESP_OK && "Failed to begin transmitting");
64.   printf("Transmitters Running\n");
65. }

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gives result "no free tx channels" when attempting to open third channel

Code: [Select all] [Expand/Collapse]

1. ESP32S3 RMT !KHz three phase sync test
2. setting up channel 0
3. I (322) gpio: GPIO[16]| InputEn: 0| OutputEn: 1| OpenDrain: 0| Pullup: 1| Pulldown: 0| Intr:0
4. setting up channel 1
5. I (332) gpio: GPIO[17]| InputEn: 0| OutputEn: 1| OpenDrain: 0| Pullup: 1| Pulldown: 0| Intr:0
6. setting up channel 2
7. E (342) rmt: rmt_tx_register_to_group(152): no free tx channels
8. E (352) rmt: rmt_new_tx_channel(288): register channel failed

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the ESP32S3 technical reference states it has four Tx channels???

any idea on what the problem is?

[ESP_Sprite]

Odd, as far as I can see that code should work. What ESP-IDF version is this?

[horace99]

version is esp-idf-v5.3.1

originally had this problem using the Arduino IDE - see https://forum.arduino.cc/t/esp32s3-rmt- ... el/1310503

thought it may just be an Arduino ESP32 problem so tried the ESP-IDF to check - same problem

using two RMT Tx channels works OK

[nopnop2002]

This seems to be a bug in the ESP-IDF component when memory block symbol and SOC_RMT_MEM_WORDS_PER_CHANNEL do not match.

Code: Select all

$ grep -rn "#define SOC_RMT_MEM_WORDS_PER_CHANNEL" *
esp32/include/soc/soc_caps.h:278:#define SOC_RMT_MEM_WORDS_PER_CHANNEL   64 /*!< Each channel owns 64 words memory */
esp32c3/include/soc/soc_caps.h:243:#define SOC_RMT_MEM_WORDS_PER_CHANNEL         48 /*!< Each channel owns 48 words memory (1 word = 4 Bytes) */
esp32c5/mp/include/soc/soc_caps.h:308:#define SOC_RMT_MEM_WORDS_PER_CHANNEL         48 /*!< Each channel owns 48 words memory (1 word = 4 Bytes) */
esp32c5/beta3/include/soc/soc_caps.h:313:#define SOC_RMT_MEM_WORDS_PER_CHANNEL         48 /*!< Each channel owns 48 words memory (1 word = 4 Bytes) */
esp32c6/include/soc/soc_caps.h:310:#define SOC_RMT_MEM_WORDS_PER_CHANNEL         48 /*!< Each channel owns 48 words memory (1 word = 4 Bytes) */
esp32c61/include/soc/soc_caps.h:305:#define SOC_RMT_MEM_WORDS_PER_CHANNEL         48 /*!< Each channel owns 48 words memory (1 word = 4 Bytes) */
esp32h2/include/soc/soc_caps.h:304:#define SOC_RMT_MEM_WORDS_PER_CHANNEL         48 /*!< Each channel owns 48 words memory (1 word = 4 Bytes) */
esp32p4/include/soc/soc_caps.h:374:#define SOC_RMT_MEM_WORDS_PER_CHANNEL         48 /*!< Each channel owns 48 words memory (1 word = 4 Bytes) */
esp32s2/include/soc/soc_caps.h:260:#define SOC_RMT_MEM_WORDS_PER_CHANNEL         64 /*!< Each channel owns 64 words memory (1 word = 4 Bytes) */
esp32s3/include/soc/soc_caps.h:269:#define SOC_RMT_MEM_WORDS_PER_CHANNEL         48 /*!< Each channel owns 48 words memory (1 word = 4 Bytes) */

Basically, we need to fix a bug in ESP-IDF when memory block symbols and SOC_RMT_MEM_WORDS_PER_CHANNEL do not match.
But for ESP32S3 the following changes may work.

Code: Select all

    rmt_tx_channel_config_t tx_chan_config = {
      .gpio_num = tx_gpio_number[i],
      .clk_src = RMT_CLK_SRC_DEFAULT,
      .resolution_hz = 1 * 1000 * 1000,  // 1MHz clock
#if 0
      .mem_block_symbols = 64,
#endif
      .mem_block_symbols = 48,
      .trans_queue_depth = 1,
    };

There is a description like this below.
https://docs.espressif.com/projects/esp ... s/rmt.html

Code: Select all

Increase the rmt_tx_channel_config_t::mem_block_symbols, in steps of 48.

If SOC_RMT_MEM_WORDS_PER_CHANNEL is 48 and mem_block_symbols is 64, 2 blocks of memory are required, but there is a bug when using 2 blocks of memory.
When using 2 blocks of memory, up to 4 channels can be used according to the specifications.

I've reported a bug here.
https://github.com/espressif/esp-idf/issues/14736

[horace99]

thanks, that fixed it!
updated code as suggested and in addition fixed timing of pulsePattern3

Code: [Select all] [Expand/Collapse]

1. #include <stdio.h>
2. #include <stdbool.h>
3. #include <unistd.h>
4. // ESP32S3 RMT 1KHz three phase square wave  sync test
5.  
6.  
7. #include "driver/rmt_tx.h"
8.  
9. void app_main(void)
10. {
11. //    while (true) {
12.  //       printf("Hello from app_main!\n");
13.  //       sleep(1);
14.  //   }
15.  printf("ESP32S3 RMT !KHz three phase sync test\n");
16.   //delay(2000);
17.   // setup Tx channels
18.   rmt_channel_handle_t tx_channels[3] = { NULL };
19.   gpio_num_t tx_gpio_number[3] = { GPIO_NUM_16, GPIO_NUM_17, GPIO_NUM_18 };  // pin numbers
20.   for (int i = 0; i < 3; i++) {
21.     printf("setting up channel %d\n", i);
22.     rmt_tx_channel_config_t tx_chan_config = {
23.       .gpio_num = tx_gpio_number[i],
24.       .clk_src = RMT_CLK_SRC_DEFAULT,
25.       .resolution_hz = 1 * 1000 * 1000,  // 1MHz clock
26. #if 0
27.       .mem_block_symbols = 64,
28. #endif
29.       .mem_block_symbols = 48,      .trans_queue_depth = 1,
30.     };
31.     ESP_ERROR_CHECK(rmt_new_tx_channel(&tx_chan_config, &tx_channels[i]));
32.   }
33.   rmt_transmit_config_t transmitConfig = {
34.     .loop_count = -1
35.   };
36.   rmt_encoder_handle_t copyEncoder =NULL;
37.   rmt_copy_encoder_config_t copyEncoderConfig = {};
38.   assert(rmt_new_copy_encoder(&copyEncoderConfig, &copyEncoder) == ESP_OK && "Failed to Create Copy Encoder");
39.   ESP_ERROR_CHECK(rmt_enable(tx_channels[2]));
40.   ESP_ERROR_CHECK(rmt_enable(tx_channels[1]));
41.   ESP_ERROR_CHECK(rmt_enable(tx_channels[0]));
42.  
43.   // setup sync manage for the three pulses
44.   rmt_sync_manager_handle_t synchro = NULL;
45.   rmt_sync_manager_config_t synchro_config = {
46.     .tx_channel_array = tx_channels,
47.     .array_size = sizeof(tx_channels) / sizeof(tx_channels[0]),
48.   };
49.   ESP_ERROR_CHECK(rmt_new_sync_manager(&synchro_config, &synchro));
50.  
51.   printf("Starting Transmitters\n");
52.   // setup pulse patterns - clock is 1MHz
53.   // two 200KHz pulses 40% duty cycle
54.   const rmt_symbol_word_t pulsePattern1[] = {
55.     { .duration0 = 500, .level0 = 1, .duration1 = 500, .level1 = 0 },
56.   };
57.   const rmt_symbol_word_t pulsePattern2[] = {
58.     { .duration0 = 333, .level0 = 0, .duration1 = 500, .level1 = 1 },
59.     { .duration0 = 100, .level0 = 0, .duration1 = 67, .level1 = 0 },
60.   };
61.     const rmt_symbol_word_t pulsePattern3[] = {
62.     { .duration0 = 133, .level0 = 1, .duration1 = 500, .level1 = 0 },
63.     { .duration0 = 100, .level0 = 1, .duration1 = 267, .level1 = 1 },
64.   };
65.  
66.   assert(rmt_transmit(tx_channels[0], copyEncoder, &pulsePattern1, sizeof(pulsePattern1), &transmitConfig) == ESP_OK && "Failed to begin transmitting");
67.   assert(rmt_transmit(tx_channels[1], copyEncoder, &pulsePattern2, sizeof(pulsePattern2), &transmitConfig) == ESP_OK && "Failed to begin transmitting");
68.   assert(rmt_transmit(tx_channels[2], copyEncoder, &pulsePattern3, sizeof(pulsePattern3), &transmitConfig) == ESP_OK && "Failed to begin transmitting");
69.   printf("Transmitters Running\n");
70. }

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terminal reports

Code: [Select all] [Expand/Collapse]

1. ESP32S3 RMT !KHz three phase sync test
2. setting up channel 0
3. I (318) gpio: GPIO[16]| InputEn: 0| OutputEn: 1| OpenDrain: 0| Pullup: 1| Pulldown: 0| Intr:0
4. setting up channel 1
5. I (328) gpio: GPIO[17]| InputEn: 0| OutputEn: 1| OpenDrain: 0| Pullup: 1| Pulldown: 0| Intr:0
6. setting up channel 2
7. I (338) gpio: GPIO[18]| InputEn: 0| OutputEn: 1| OpenDrain: 0| Pullup: 1| Pulldown: 0| Intr:0
8. Starting Transmitters
9. Transmitters Running
10. I (348) main_task: Returned from app_main()

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