avr/serial.c

   1 /*
   2  * (C) Copyright 2014 Leo C. <erbl259-lmu@yahoo.de>
   3  *
   4  * SPDX-License-Identifier:     GPL-2.0+
   5  */
   6
   7 #include <avr/io.h>
   8 #include <avr/interrupt.h>
   9 #include <util/atomic.h>
  10 #include <errno.h>
  11 #include <stdio.h>
  12
  13 #include "ring.h"
  14 #include "serial.h"
  15
  16
  17 static int _write(char c, FILE *stream);
  18 static FILE mystdout = FDEV_SETUP_STREAM(_write,
  19                 NULL, _FDEV_SETUP_WRITE);
  20
  21
  22
  23 #define BUFFER_SIZE 128
  24
  25 #if ((BUFFER_SIZE-1) & BUFFER_SIZE)
  26 # error: BUFFER_SIZE not power of 2
  27 #endif
  28
  29 #if ((BUFFER_SIZE) > 256)
  30 # error: BUFFER_SIZE
  31 #endif
  32
  33 struct ring rx_ring;
  34 struct ring tx_ring;
  35 uint8_t rx_ring_buffer[BUFFER_SIZE];
  36 uint8_t tx_ring_buffer[BUFFER_SIZE];
  37
  38
  39
  40 /* Initialize UART */
  41
  42 void usart0_setup(unsigned long baud) {
  43
  44         ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
  45
  46                 PRR0 &= ~_BV(PRUSART0);
  47                 UCSR0B = 0;
  48
  49                 /* Initialize ring buffers. */
  50                 ring_init(&rx_ring, rx_ring_buffer, BUFFER_SIZE);
  51                 ring_init(&tx_ring, tx_ring_buffer, BUFFER_SIZE);
  52
  53                 UCSR0A = 0;
  54                 UBRR0  = F_CPU / baud / 16 - 1;
  55                 UCSR0B = _BV(RXCIE0) | _BV(RXEN0) | _BV(TXEN0);
  56                 UCSR0C = 3 << UCSZ00;
  57         };
  58 }
  59
  60 /*--------------------------------------------------------------------------*/
  61
  62 /* UART RXC interrupt */
  63
  64 ISR(USART0_RX_vect)
  65 {
  66         uint8_t d;
  67
  68         d = UDR0;
  69         ring_write_ch(&rx_ring, d);
  70 }
  71
  72 /* UART UDRE interrupt */
  73
  74 ISR(USART0_UDRE_vect)
  75 {
  76         int d = ring_read_ch(&tx_ring);
  77
  78         if (d < 0) {
  79                 /* Disable TX empty interrupt. */
  80                 UCSR0B = _BV(RXCIE0) | _BV(RXEN0) | _BV(TXEN0);
  81         } else {
  82                 UDR0 = d;
  83         }
  84 }
  85
  86 /*--------------------------------------------------------------------------*/
  87
  88 void serial_setup(unsigned long baud)
  89 {
  90         stdout = &mystdout;
  91         usart0_setup(baud);
  92 }
  93
  94 /*--------------------------------------------------------------------------*/
  95
  96 int _write(char c, FILE *stream)
  97 {
  98         (void) stream;
  99
 100         if (c == '\n')
 101                 serial_putc('\r');
 102         serial_putc(c);
 103
 104         return 0;
 105 }
 106
 107 int serial_getc(void)
 108 {
 109         return ring_read_ch(&rx_ring);
 110 }
 111
 112 void serial_putc(char data)
 113 {
 114         while (ring_write_ch(&tx_ring, data) < 0)
 115                 ;
 116
 117         /* Enable the TXE interrupt. */
 118         UCSR0B = _BV(RXCIE0) | _BV(RXEN0) | _BV(TXEN0) | _BV(UDRIE0);
 119 }
 120
 121 uint_fast8_t serial_tstc(void)
 122 {
 123         return !ring_is_empty(&rx_ring);
 124 }