protocol/serial_soft.c

   1 /*
   2 Copyright 2012 Jun WAKO <wakojun@gmail.com>
   3
   4 This software is licensed with a Modified BSD License.
   5 All of this is supposed to be Free Software, Open Source, DFSG-free,
   6 GPL-compatible, and OK to use in both free and proprietary applications.
   7 Additions and corrections to this file are welcome.
   8
   9
  10 Redistribution and use in source and binary forms, with or without
  11 modification, are permitted provided that the following conditions are met:
  12
  13 * Redistributions of source code must retain the above copyright
  14   notice, this list of conditions and the following disclaimer.
  15
  16 * Redistributions in binary form must reproduce the above copyright
  17   notice, this list of conditions and the following disclaimer in
  18   the documentation and/or other materials provided with the
  19   distribution.
  20
  21 * Neither the name of the copyright holders nor the names of
  22   contributors may be used to endorse or promote products derived
  23   from this software without specific prior written permission.
  24
  25 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  26 AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  27 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  28 ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
  29 LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  30 CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  31 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  32 INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  33 CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  34 ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  35 POSSIBILITY OF SUCH DAMAGE.
  36 */
  37
  38 #include <stdbool.h>
  39 #include <avr/io.h>
  40 #include <avr/interrupt.h>
  41 #include <util/delay.h>
  42 #include "serial.h"
  43
  44 /*
  45  *  Stupid Inefficient Busy-wait Software Serial
  46  *  is still useful for negative logic signal like Sun protocol not supported by hardware USART.
  47  */
  48
  49 #define WAIT_US     (1000000/SERIAL_BAUD)
  50
  51 void serial_init(void)
  52 {
  53     SERIAL_RXD_INIT();
  54     SERIAL_TXD_INIT();
  55 }
  56
  57 /* RX ring buffer */
  58 #define RBUF_SIZE   8
  59 static uint8_t rbuf[RBUF_SIZE];
  60 static uint8_t rbuf_head = 0;
  61 static uint8_t rbuf_tail = 0;
  62
  63 uint8_t serial_recv(void)
  64 {
  65     uint8_t data = 0;
  66     if (rbuf_head == rbuf_tail) {
  67         return 0;
  68     }
  69
  70     data = rbuf[rbuf_tail];
  71     rbuf_tail = (rbuf_tail + 1) % RBUF_SIZE;
  72     return data;
  73 }
  74
  75 void serial_send(uint8_t data)
  76 {
  77     /* signal state: IDLE: ON, START: OFF, STOP: ON, DATA0: OFF, DATA1: ON */
  78     /* start bit */
  79     SERIAL_TXD_OFF();
  80     _delay_us(WAIT_US);
  81
  82 #ifdef SERIAL_BIT_ORDER_MSB
  83     uint8_t mask = 0x80;
  84 #else
  85     uint8_t mask = 0x01;
  86 #endif
  87     while (mask) {
  88         if (data&mask) { SERIAL_TXD_ON(); } else { SERIAL_TXD_OFF(); }
  89         _delay_us(WAIT_US);
  90
  91 #ifdef SERIAL_BIT_ORDER_MSB
  92         mask >>= 1;
  93 #else
  94         mask <<= 1;
  95 #endif
  96     }
  97
  98     /* stop bit */
  99     SERIAL_TXD_ON();
 100     _delay_us(WAIT_US);
 101 }
 102
 103 /* detect edge of start bit */
 104 ISR(SERIAL_RXD_VECT)
 105 {
 106     SERIAL_RXD_INT_ENTER()
 107
 108     uint8_t data = 0;
 109 #ifdef SERIAL_BIT_ORDER_MSB
 110     uint8_t mask = 0x80;
 111 #else
 112     uint8_t mask = 0x01;
 113 #endif
 114     /* to center of start bit */
 115     _delay_us(WAIT_US/2);
 116     do {
 117         /* to center of next bit */
 118         _delay_us(WAIT_US);
 119
 120         if (SERIAL_RXD_READ()) {
 121             data |= mask;
 122         }
 123 #ifdef SERIAL_BIT_ORDER_MSB
 124         mask >>= 1;
 125 #else
 126         mask <<= 1;
 127 #endif
 128     } while (mask);
 129     /* to center of stop bit */
 130     _delay_us(WAIT_US);
 131
 132     uint8_t next = (rbuf_head + 1) % RBUF_SIZE;
 133     if (next != rbuf_tail) {
 134         rbuf[rbuf_head] = data;
 135         rbuf_head = next;
 136     }
 137
 138     SERIAL_RXD_INT_EXIT();
 139 }