drivers/periph/uart: add periph_uart_rx_start feature

drivers/include/periph/uart.h

@@ -98,13 +98,24 @@ typedef unsigned int uart_t;
  */
 typedef void(*uart_rx_cb_t)(void *arg, uint8_t data);
 
+/**
+ * @brief   Signature for receive start condition interrupt callback
+ *
+ * @param[in] arg           context to the callback (optional)
+ */
+typedef void(*uart_rxstart_cb_t)(void *arg);
+
 /**
  * @brief   Interrupt context for a UART device
  */
 #ifndef HAVE_UART_ISR_CTX_T
 typedef struct {
     uart_rx_cb_t rx_cb;     /**< data received interrupt callback */
-    void *arg;              /**< argument to both callback routines */
+    void *arg;              /**< argument to data received callback */
+#ifdef MODULE_PERIPH_UART_RXSTART_IRQ
+    uart_rxstart_cb_t rxs_cb;   /**< start condition received interrupt callback */
+    void *rxs_arg;          /**< argument to start condition received callback */
+#endif
 } uart_isr_ctx_t;
 #endif
 
@@ -243,6 +254,45 @@ gpio_t uart_pin_tx(uart_t uart);
 #endif /* DOXYGEN */
 #endif /* MODULE_PERIPH_UART_RECONFIGURE */
 
+#if defined(MODULE_PERIPH_UART_RXSTART_IRQ) || DOXYGEN
+
+/**
+ * @brief   Configure the function that will be called when a start condition
+ *          is detected.
+ *
+ *          This will not enable / disable the generation of the RX start
+ *          interrupt.
+ *
+ * @note    You have to add the module `periph_uart_rxstart_irq` to your project
+ *          to enable this function
+ *
+ * @param[in] uart      The device to configure
+ * @param[in] cb        The function called when a start condition is detected
+ * @param[in] arg       Optional function argument
+ */
+void uart_rxstart_irq_configure(uart_t uart, uart_rxstart_cb_t cb, void *arg);
+
+/**
+ * @brief   Enable the RX start interrupt.
+ *
+ * @note    You have to add the module `periph_uart_rxstart_irq` to your project
+ *          to enable this function
+ *
+ * @param[in] uart      The device to configure
+ */
+void uart_rxstart_irq_enable(uart_t uart);
+
+/**
+ * @brief   Disable the RX start interrupt.
+ *
+ * @note    You have to add the module `periph_uart_rxstart_irq` to your project
+ *          to enable this function
+ *
+ * @param[in] uart      The device to configure
+ */
+void uart_rxstart_irq_disable(uart_t uart);
+#endif /* MODULE_PERIPH_UART_RXSTART_IRQ */
+
 /**
  * @brief   Setup parity, data and stop bits for a given UART device
  *

drivers/periph_common/Kconfig.uart

@@ -32,6 +32,10 @@ config MODULE_PERIPH_UART_NONBLOCKING
     bool "Non-blocking support"
     depends on HAS_PERIPH_UART_NONBLOCKING
 
+config MODULE_PERIPH_UART_RXSTART_IRQ
+    bool "Enable Start Condition Interrupt"
+    depends on HAS_PERIPH_UART_RXSTART_IRQ
+
 config MODULE_PERIPH_INIT_UART_MODECFG
     bool
     depends on MODULE_PERIPH_UART_MODECFG

kconfigs/Kconfig.features

@@ -333,6 +333,11 @@ config HAS_PERIPH_UART_RECONFIGURE
     help
         Indicates that the UART pins can be re-configured as GPIOs.
 
+config HAS_PERIPH_UART_RXSTART_IRQ
+    bool
+    help
+        Indicates that the UART has an Interrupt for Start Condition detected.
+
 config HAS_PERIPH_USBDEV
     bool
     help