feat(rmt): Add simple callback encoder

components/esp_driver_rmt/include/driver/rmt_encoder.h

@@ -68,6 +68,47 @@ struct rmt_encoder_t {
     esp_err_t (*del)(rmt_encoder_t *encoder);
 };
 
+/**
+ * @brief Callback for simple callback encoder
+ *
+ * This will get called to encode the data stream of given length (as passed to
+ * rmt_transmit by the user) into symbols to be sent by the hardware.
+ *
+ * The callback will be initially called with symbol_pos=0. If the callback
+ * encodes N symbols and finishes, the next callback will always be with
+ * symbols_written=N. If the callback then encodes M symbols, the next callback
+ * will always be with symbol_pos=N+M, etc. The only exception is when the
+ * encoder is reset (e.g. to begin a new transaction) in which case
+ * symbol_pos will always restart at 0.
+ *
+ * If the amount of free space in the symbol buffer (as indicated by
+ * symbols_free) is too low, the function can return 0 as result and
+ * the RMT will call the function again once there is more space available.
+ * Note that the callback should eventually return non-0 if called with
+ * free space of rmt_simple_encoder_config_t::min_chunk_size or more. It
+ * is acceptable to return 0 for a given free space N, then on the next
+ * call (possibly with a larger free buffer space) return less or more
+ * than N symbols.
+ *
+ * When the transaction is done (all data_size data is encoded), the callback
+ * can indicate this by setting *done to true. This can either happen on the
+ * last callback call that returns an amount of symbols encoded, or on a
+ * callback that returns zero. In either case, the callback will not be
+ * called again for this transaction.
+ *
+ * @param[in] data Data pointer, as passed to rmt_transmit()
+ * @param[in] data_size Size of the data, as passed to rmt_transmit()
+ * @param[in] symbols_written Current position in encoded stream, in symbols
+ * @param[in] symbols_free The maximum amount of symbols that can be written into the `symbols` buffer
+ * @param[out] symbols Symbols to be sent to the RMT hardware
+ * @param[out] done Setting this to true marks this transaction as finished
+ * @param arg Opaque argument
+ * @return Amount of symbols encoded in this callback round. 0 if more space is needed.
+ */
+typedef size_t (*rmt_encode_simple_cb_t)(const void *data, size_t data_size,
+                                         size_t symbols_written, size_t symbols_free,
+                                         rmt_symbol_word_t *symbols, bool *done, void *arg);
+
 /**
  * @brief Bytes encoder configuration
  */
@@ -85,6 +126,18 @@ typedef struct {
 typedef struct {
 } rmt_copy_encoder_config_t;
 
+/**
+ * @brief Simple callback encoder configuration
+ */
+typedef struct {
+    rmt_encode_simple_cb_t callback;  /*!< Callback to call for encoding data into RMT items */
+    void *arg;                        /*!< Opaque user-supplied argument for callback */
+    size_t min_chunk_size;            /*!< Minimum amount of free space, in RMT symbols, the
+                                           encoder needs in order to guarantee it always
+                                           returns non-zero. Defaults
+                                           to 64 if zero / not given. */
+} rmt_simple_encoder_config_t;
+
 /**
  * @brief Create RMT bytes encoder, which can encode byte stream into RMT symbols
  *
@@ -126,6 +179,20 @@ esp_err_t rmt_bytes_encoder_update_config(rmt_encoder_handle_t bytes_encoder, co
  */
 esp_err_t rmt_new_copy_encoder(const rmt_copy_encoder_config_t *config, rmt_encoder_handle_t *ret_encoder);
 
+/**
+ * @brief Create RMT simple callback encoder, which uses a callback to convert incoming
+ *        data into RMT symbols.
+ *
+ * @param[in] config Simple callback encoder configuration
+ * @param[out] ret_encoder Returned encoder handle
+ * @return
+ *      - ESP_OK: Create RMT simple callback encoder successfully
+ *      - ESP_ERR_INVALID_ARG: Create RMT simple callback encoder failed because of invalid argument
+ *      - ESP_ERR_NO_MEM: Create RMT simple callback encoder failed because out of memory
+ *      - ESP_FAIL: Create RMT simple callback encoder failed because of other error
+ */
+esp_err_t rmt_new_simple_encoder(const rmt_simple_encoder_config_t *config, rmt_encoder_handle_t *ret_encoder);
+
 /**
  * @brief Delete RMT encoder
  *