avr/serial.c

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