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                 UCSR0A = 0;
  49                 UBRR0  = (F_CPU + (baud/2) + 8) / baud / 16 - 1;
  50                 UCSR0B = _BV(RXCIE0) | _BV(RXEN0) | _BV(TXEN0);
  51                 UCSR0C = 3 << UCSZ00;
  52
  53                 /* Initialize ring buffers. */
  54                 ring_init(&rx_ring, rx_ring_buffer, BUFFER_SIZE);
  55                 ring_init(&tx_ring, tx_ring_buffer, BUFFER_SIZE);
  56         };
  57 }
  58
  59 /*--------------------------------------------------------------------------*/
  60
  61 /* UART RXC interrupt */
  62
  63 ISR(USART0_RX_vect)
  64 {
  65         uint8_t d;
  66
  67         d = UDR0;
  68         ring_write_ch(&rx_ring, d);
  69 }
  70
  71 /* UART UDRE interrupt */
  72
  73 ISR(USART0_UDRE_vect)
  74 {
  75         int d = ring_read_ch(&tx_ring);
  76
  77         if (d < 0) {
  78                 /* Disable TX empty interrupt. */
  79                 UCSR0B = _BV(RXCIE0) | _BV(RXEN0) | _BV(TXEN0);
  80         } else {
  81                 UDR0 = d;
  82         }
  83 }
  84
  85 /*--------------------------------------------------------------------------*/
  86
  87 void serial_setup(unsigned long baud)
  88 {
  89         stdout = &mystdout;
  90         usart0_setup(baud);
  91 }
  92
  93 /*--------------------------------------------------------------------------*/
  94
  95 int _write(char c, FILE *stream)
  96 {
  97         (void) stream;
  98
  99         if (c == '\n')
 100                 serial_putc('\r');
 101         serial_putc(c);
 102
 103         return 0;
 104 }
 105
 106 int serial_getc(void)
 107 {
 108         return ring_read_ch(&rx_ring);
 109 }
 110
 111 void serial_putc(char data)
 112 {
 113         while (ring_write_ch(&tx_ring, data) < 0)
 114                 ;
 115
 116         /* Enable the TXE interrupt. */
 117         UCSR0B = _BV(RXCIE0) | _BV(RXEN0) | _BV(TXEN0) | _BV(UDRIE0);
 118 }
 119
 120 uint_fast8_t serial_tstc(void)
 121 {
 122         return !ring_is_empty(&rx_ring);
 123 }