Merge branch 'feature/uart_get_free_tx_buffer_size_v4.4' into 'release/v4.4'

uart: Add a new API to get the free space size of tx buffer (backport v4.4)

See merge request espressif/esp-idf!18977

Author: jack0c

components/driver/include/driver/uart.h

@@ -594,6 +594,18 @@ esp_err_t uart_flush_input(uart_port_t uart_num);
  */
 esp_err_t uart_get_buffered_data_len(uart_port_t uart_num, size_t* size);
 
+/**
+ * @brief   UART get TX ring buffer free space size
+ *
+ * @param   uart_num UART port number, the max port number is (UART_NUM_MAX -1).
+ * @param   size Pointer of size_t to accept the free space size
+ *
+ * @return
+ *     - ESP_OK Success
+ *     - ESP_ERR_INVALID_ARG Parameter error
+ */
+esp_err_t uart_get_tx_buffer_free_size(uart_port_t uart_num, size_t *size);
+
 /**
  * @brief   UART disable pattern detect function.
  *          Designed for applications like 'AT commands'.

components/driver/uart.c

@@ -1343,6 +1343,15 @@ esp_err_t uart_get_buffered_data_len(uart_port_t uart_num, size_t *size)
     return ESP_OK;
 }
 
+esp_err_t uart_get_tx_buffer_free_size(uart_port_t uart_num, size_t *size)
+{
+    ESP_RETURN_ON_FALSE((uart_num < UART_NUM_MAX), ESP_ERR_INVALID_ARG, UART_TAG, "uart_num error");
+    ESP_RETURN_ON_FALSE((p_uart_obj[uart_num]), ESP_ERR_INVALID_ARG, UART_TAG, "uart driver error");
+    ESP_RETURN_ON_FALSE((size != NULL), ESP_ERR_INVALID_ARG, UART_TAG, "arg pointer is NULL");
+    *size = p_uart_obj[uart_num]->tx_buf_size - p_uart_obj[uart_num]->tx_len_tot;
+    return ESP_OK;
+}
+
 esp_err_t uart_flush(uart_port_t uart_num) __attribute__((alias("uart_flush_input")));
 
 esp_err_t uart_flush_input(uart_port_t uart_num)