SerialX.flush() - now wait until TC Complete

SerialX.flush() - now waits until the TX completes...
Looks at the TC flag of the uart to know when it has completed
the transfer.

Moved the flush() function to .cpp file as it now uses the device header
file which is only included in the .cpp file

Author: KurtE

Diff for: cores/arduino/zephyrSerial.cpp

@@ -189,6 +189,16 @@ size_t arduino::ZephyrSerial::write(const uint8_t *buffer, size_t size)
 	return size;
 }
 
+void arduino::ZephyrSerial::flush() {
+	while (ring_buf_size_get(&tx.ringbuf) > 0) {
+		k_yield();
+	}
+	while (uart_irq_tx_complete(uart) == 0){
+		k_yield();
+	}
+}
+
+
 #if DT_NODE_HAS_PROP(DT_PATH(zephyr_user), serials)
 #if !DT_NODE_HAS_PROP(DT_PATH(zephyr_user), cdc_acm)
 // If CDC USB, use that object as Serial (and SerialUSB)

Diff for: cores/arduino/zephyrSerial.h

@@ -51,11 +51,7 @@ class ZephyrSerial : public HardwareSerial
 	ZephyrSerial(const struct device *dev) : uart(dev) { }
 	void begin(unsigned long baudrate, uint16_t config);
 	void begin(unsigned long baudrate) { begin(baudrate, SERIAL_8N1); }
-	void flush() {
-		while (ring_buf_size_get(&tx.ringbuf) > 0) {
-			k_yield();
-		}
-	}
+	void flush();
 	void end() { }
 	size_t write(const uint8_t *buffer, size_t size);
 	size_t write(const uint8_t data) { return write(&data, 1); }