From a07beb97685caed5ddf203d27051c7318e2e5e56 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bart=C5=82omiej=20Przemys=C5=82aw=20Pluta?=
 <noreply.git@mx.bartlomiejpluta.com>
Date: Wed, 18 Nov 2020 18:11:15 +0100
Subject: [PATCH] Create simple UART library

---
 firmware/uart.c | 74 +++++++++++++++++++++++++++++++++++++++++++++++++
 firmware/uart.h | 20 +++++++++++++
 2 files changed, 94 insertions(+)
 create mode 100755 firmware/uart.c
 create mode 100755 firmware/uart.h

diff --git a/firmware/uart.c b/firmware/uart.c
new file mode 100755
index 0000000..cd02a42
--- /dev/null
+++ b/firmware/uart.c
@@ -0,0 +1,74 @@
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include <stdlib.h>
+#include "uart.h"
+
+// Ring buffer macros
+#define RBUF(BUF_SIZE) struct { char data[BUF_SIZE]; uint8_t head; uint8_t tail; }
+#define RBUF_NEXT(BUF_IDX, MOD_MASK) (((BUF_IDX) + 1) & MOD_MASK)
+#define RBUF_FORWARD(BUF_IDX, MOD_MASK) BUF_IDX = RBUF_NEXT(BUF_IDX, MOD_MASK)
+#define RBUF_EMPTY(BUFF) (BUFF.head == BUFF.tail)
+
+volatile RBUF(UART_RX_BUF_SIZE) rx_buffer;
+volatile RBUF(UART_TX_BUF_SIZE) tx_buffer;
+
+void uart_init(void)
+{
+	UBRRH = (uint8_t) (__UBRR>>8);
+	UBRRL = (uint8_t) __UBRR;
+
+	UCSRB = (1<<RXEN) | (1<<TXEN) | (1<<RXCIE);
+	UCSRC = (1<<URSEL) | (3<<UCSZ0);
+}
+
+void uart_putc(char data)
+{
+	uint8_t head = RBUF_NEXT(tx_buffer.head, UART_TX_BUF_MASK);
+
+  while(head == tx_buffer.tail);
+
+  tx_buffer.data[head] = data;
+  tx_buffer.head = head;
+
+  UCSRB |= (1<<UDRIE);
+}
+
+void uart_puts(char* str)
+{
+  register char c;
+  while ((c = *str++)) uart_putc(c);
+}
+
+void uart_puti(int16_t value, int16_t radix)
+{
+	char number[20];
+	itoa(value, number, radix);
+	uart_puts(number);
+}
+
+char uart_getc(void)
+{
+  if(RBUF_EMPTY(rx_buffer)) return 0;
+  RBUF_FORWARD(rx_buffer.tail, UART_RX_BUF_MASK);
+  return rx_buffer.data[rx_buffer.tail];
+}
+
+ISR(USART_UDRE_vect)
+{    
+  if(!RBUF_EMPTY(tx_buffer)) 
+	{
+    RBUF_FORWARD(tx_buffer.tail, UART_TX_BUF_MASK);
+    UDR = tx_buffer.data[tx_buffer.tail];
+  } 
+	else 
+	{
+		UCSRB &= ~(1<<UDRIE);
+  }
+}
+
+ISR(USART_RXC_vect)
+{
+  RBUF_FORWARD(rx_buffer.head, UART_RX_BUF_MASK);
+	rx_buffer.data[rx_buffer.head] = UDR;
+}
+
diff --git a/firmware/uart.h b/firmware/uart.h
new file mode 100755
index 0000000..a586c11
--- /dev/null
+++ b/firmware/uart.h
@@ -0,0 +1,20 @@
+#ifndef __UART_H__
+#define __UART_H__
+
+
+#define UART_BAUD 9600
+#define __UBRR ((F_CPU + 8UL*UART_BAUD) / (16UL*UART_BAUD) - 1)
+
+#define UART_RX_BUF_SIZE 32
+#define UART_RX_BUF_MASK (UART_RX_BUF_SIZE-1)
+
+#define UART_TX_BUF_SIZE 16
+#define UART_TX_BUF_MASK (UART_TX_BUF_SIZE-1)
+
+void uart_init(void);
+char uart_getc(void);
+void uart_putc(char data);
+void uart_puts(char *str);
+void uart_puti(int16_t value, int16_t radix);
+
+#endif