Merge pull request #13862 from jeromecoutant/PR_RTS_FREE

STM32 SERIAL: free RTS/CTS pins

Author: 0xc0170

targets/TARGET_STM/TARGET_STM32L4/serial_device.c

@@ -667,6 +667,7 @@ static void _serial_set_flow_control_direct(serial_t *obj, FlowControl type, con
     if (type == FlowControlRTS) {
         // Enable RTS
         MBED_ASSERT(pinmap->rx_flow_pin != NC);
+        obj_s->hw_flow_ctl = UART_HWCONTROL_RTS;
         obj_s->pin_rts = pinmap->rx_flow_pin;
         // Enable the pin for RTS function
         pin_function(pinmap->rx_flow_pin, pinmap->rx_flow_function);

targets/TARGET_STM/serial_api.c

@@ -355,6 +355,15 @@ void serial_free(serial_t *obj)
 
     pin_function(obj_s->pin_rx, STM_PIN_DATA(STM_MODE_INPUT, GPIO_NOPULL, 0));
 
+#if DEVICE_SERIAL_FC
+    if ( (obj_s->hw_flow_ctl == UART_HWCONTROL_RTS) || (obj_s->hw_flow_ctl == UART_HWCONTROL_RTS_CTS) ) {
+        pin_function(obj_s->pin_rts, STM_PIN_DATA(STM_MODE_INPUT, GPIO_NOPULL, 0));
+    }
+    if ( (obj_s->hw_flow_ctl == UART_HWCONTROL_CTS) || (obj_s->hw_flow_ctl == UART_HWCONTROL_RTS_CTS) ) {
+        pin_function(obj_s->pin_cts, STM_PIN_DATA(STM_MODE_INPUT, GPIO_NOPULL, 0));
+    }
+#endif
+
     serial_irq_ids[obj_s->index] = 0;
 }