RMT callback delay

[Nikd00]

Hi,

for my project I need to set 4 gpio outputs based on signal in form of very short pulses (tens of ns) and speed is crucial. I think RMT is great for reading the pulses, however, the callback seems to have a high latency. The code below is simplified ir_nec_transceiver example. So far it only toggles the output pin 32 when pulses are received. It takes roughly 7 us from receiving the last pulse to modifying the output. Is there any way to reduce the delay?

Code: [Select all] [Expand/Collapse]

1. #include "freertos/FreeRTOS.h"
2. #include "freertos/task.h"
3. #include "freertos/queue.h"
4. #include "esp_log.h"
5. #include "driver/rmt_rx.h"
6. #include "soc/soc.h"
7. #include "soc/gpio_reg.h"
8.  
9. #define OUTPUT_PINS_START 32
10. #define OUTPUT_PINS 1111 << (OUTPUT_PINS_START-32)
11.  
12. #define RMT_RESOLUTION_HZ     80000000
13. #define RMT_RX_GPIO_NUM       19
14. #define RMT_MIN_DURATION      25
15. #define RMT_MAX_DURATION      400
16. #define RMT_BUFFER_SIZE       64
17.  
18. static const char *TAG = "mux";
19.  
20. uint32_t output_value = 0;
21.  
22. rmt_channel_handle_t rx_channel = NULL;
23. rmt_receive_config_t receive_config = {
24.     .signal_range_min_ns = RMT_MIN_DURATION, // A pulse whose width is smaller than this threshold will be treated as glitch and ignored
25.     .signal_range_max_ns = RMT_MAX_DURATION, //RMT will stop receiving if one symbol level has kept more than
26. };
27. // save the received RMT symbols
28. rmt_symbol_word_t raw_symbols[RMT_BUFFER_SIZE];
29. rmt_rx_done_event_data_t rx_data;
30.  
31. static bool example_rmt_rx_done_callback(rmt_channel_handle_t channel, const rmt_rx_done_event_data_t *edata, void *user_data)
32. {
33.    
34.     output_value++;
35.     output_value &= OUTPUT_PINS;
36.     REG_WRITE(GPIO_OUT1_REG, output_value);
37.  
38.     ESP_ERROR_CHECK(rmt_receive(rx_channel, raw_symbols, sizeof(raw_symbols), &receive_config));
39.     return false;
40. }
41.  
42. void app_main(void)
43. {
44.  
45.     ESP_LOGI(TAG, "create output channels");
46.     REG_WRITE(GPIO_ENABLE1_W1TS_REG, OUTPUT_PINS);
47.  
48.     ESP_LOGI(TAG, "create RMT RX channel");
49.     rmt_rx_channel_config_t rx_channel_cfg = {
50.         .clk_src = RMT_CLK_SRC_DEFAULT,
51.         .resolution_hz = RMT_RESOLUTION_HZ,
52.         .mem_block_symbols = RMT_BUFFER_SIZE,
53.         .gpio_num = RMT_RX_GPIO_NUM,
54.     };
55.     ESP_ERROR_CHECK(rmt_new_rx_channel(&rx_channel_cfg, &rx_channel));
56.  
57.     ESP_LOGI(TAG, "register RX done callback");
58.     QueueHandle_t receive_queue = xQueueCreate(1, sizeof(rmt_rx_done_event_data_t));
59.     assert(receive_queue);
60.     rmt_rx_event_callbacks_t cbs = {
61.         .on_recv_done = example_rmt_rx_done_callback,
62.     };
63.     ESP_ERROR_CHECK(rmt_rx_register_event_callbacks(rx_channel, &cbs, receive_queue));
64.  
65.     ESP_LOGI(TAG, "enable RMT RX channel");
66.     ESP_ERROR_CHECK(rmt_enable(rx_channel));
67.  
68.     // ready to receive
69.     ESP_ERROR_CHECK(rmt_receive(rx_channel, raw_symbols, sizeof(raw_symbols), &receive_config));
70. }

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