implement uart

1 files changed, 75 insertions, 0 deletions

diff --git a/src/uart.c b/src/uart.c
new file mode 100644
index 0000000..0b65e30
--- /dev/null
+++ b/src/uart.c
@@ -0,0 +1,75 @@
+/*
+ * src/uart.c
+ * (c) 2021 Jonas Gunz <himself@jonasgunz.de>
+ * License: All rights reserved.
+ */
+
+#include "uart.h"
+
+struct ringbuff_s {
+	uint8_t buffer[256];
+	uint8_t read;
+	uint8_t write;
+} rxc_buf, txc_buf ;
+
+ISR(USART_RXC_vect) {
+	cli();
+
+	/* Discard if buffer full */
+	if( rxc_buf.read - 1 == rxc_buf.write )
+		goto end;
+
+	rxc_buf.buffer[rxc_buf.write] = UDR;
+	rxc_buf.write++;
+
+end:
+	sei();
+}
+
+ISR(USART_UDRE_vect) {
+	cli();
+
+	/* Prevent interrupt loops */
+	if( txc_buf.read == txc_buf.write ) {
+		UCSRB &= ~(1<<UDRIE);
+		goto end;
+	}
+
+	UDR = txc_buf.buffer[txc_buf.read];
+	txc_buf.read++;
+
+end:
+	sei();
+}
+
+void uart_init(){
+	memset( &txc_buf, 0, sizeof(txc_buf) );
+	memset( &rxc_buf, 0, sizeof(rxc_buf) );
+
+	UBRRH = (uint8_t)((UBRR)>>8);
+	UBRRL = (uint8_t)(UBRR);
+
+	UCSRB |= (1<<RXEN)|(1<<RXCIE)|(1<<TXEN);
+}
+
+uint8_t uart_putchar(char _c) {
+	if( txc_buf.read - 1 == txc_buf.write )
+		return 1;
+
+	txc_buf.buffer[txc_buf.write] = _c;
+	txc_buf.write ++;
+
+	UCSRB |= (1<<UDRIE);
+
+	return 0;
+}
+
+uint8_t uart_getchar(char *_c) {
+	if( rxc_buf.read == rxc_buf.write )
+		return 1;
+
+	*_c = rxc_buf.buffer[rxc_buf.read];
+	rxc_buf.read++;
+
+	return 0;
+}