Test USART reading

src/serial.c

@@ -0,0 +1,76 @@
+#include "common.h"
+#include "serial.h"
+#include <avr/io.h>
+
+#include <stdio.h>
+
+#define USART_BAUDRATE 9600
+
+// Ensure closest fit for target baudrate
+//#define BAUD_PRESCALE (((F_CPU / (USART_BAUDRATE * 16UL))) - 1)
+#define BAUD_PRESCALE ((((F_CPU / 16) + (USART_BAUDRATE / 2)) \
+        / (USART_BAUDRATE)) - 1)
+
+static char USART_Rx(void);
+static void USART_Tx(char ch);
+
+void USART_Init(void)
+{
+	UCSRB |= BIT(RXEN) | BIT(TXEN); // Enable rx and tx circuitry
+	UCSRC |= BIT(URSEL) | BIT(UCSZ0) | BIT(UCSZ1); // 8-bit chars
+	UBRRH = (BAUD_PRESCALE >> 8); // Baud Rate upper byte
+	UBRRL = BAUD_PRESCALE; // Baud rate lower byte
+}
+
+void USART_Read(char **buf, int size)
+{
+	int n = 0;
+	char *p = *buf;
+	char ch;
+
+	if ((UCSRA & BIT(RXC)) == 0) {
+		p = '\0';
+		return;
+	}
+
+	do  {
+		// Discard messages exceeding
+		// given size limit quietly
+		if (n == size) {
+			p = '\0';
+			while (USART_Rx());
+			return;
+		}
+
+		ch = USART_Rx();
+		p[n] = ch;
+		n++;
+
+	} while (ch != '\0');
+}
+
+void USART_Write(const char *buf)
+{
+	int n = 0;
+
+	while (buf[n] != '\0') {
+		USART_Tx(buf[n++]);
+	}
+}
+
+static char USART_Rx(void)
+{
+	// Anything to read from UDR?
+	if ((UCSRA & BIT(RXC)) == 0)
+		return '\0';
+
+	return UDR;
+}
+
+static void USART_Tx(char ch)
+{
+	// Wait until UDR can receive data
+	while ((UCSRA & BIT(UDRE)) == 0);
+
+	UDR = ch;
+}