utils/ucmb/microcontroller_examples/atmel_avr8/ucmb.c

   1 /*
   2  *   Microcontroller message bus
   3  *   uc-side slave implementation for Atmel AVR8
   4  *
   5  *   The gcc compiler always treats multi-byte variables as litte-endian.
   6  *   So no explicit endianness conversions are done on the message header,
   7  *   footer and status data structures.
   8  *
   9  *   Copyright (C) 2009 Michael Buesch <mb@bu3sch.de>
  10  *
  11  *   This program is free software; you can redistribute it and/or
  12  *   modify it under the terms of the GNU General Public License
  13  *   as published by the Free Software Foundation; either version 2
  14  *   of the License, or (at your option) any later version.
  15  *
  16  *   This program is distributed in the hope that it will be useful,
  17  *   but WITHOUT ANY WARRANTY; without even the implied warranty of
  18  *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19  *   GNU General Public License for more details.
  20  */
  21
  22 #include "ucmb.h"
  23
  24 #include <stdint.h>
  25 #include <avr/io.h>
  26 #include <avr/interrupt.h>
  27 #include <util/crc16.h>
  28
  29
  30 struct ucmb_message_hdr {
  31         uint16_t magic;         /* UCMB_MAGIC */
  32         uint16_t len;           /* Payload length (excluding header) */
  33 } __attribute__((packed));
  34
  35 struct ucmb_message_footer {
  36         uint16_t crc;           /* CRC of the header + payload. */
  37 } __attribute__((packed));
  38
  39 struct ucmb_status {
  40         uint16_t magic;         /* UCMB_MAGIC */
  41         uint16_t code;          /* enum ucmb_status_code */
  42 } __attribute__((packed));
  43
  44 #define UCMB_MAGIC              0x1337
  45
  46 enum ucmb_status_code {
  47         UCMB_STAT_OK = 0,
  48         UCMB_STAT_EPROTO,       /* Protocol format error */
  49         UCMB_STAT_ENOMEM,       /* Out of memory */
  50         UCMB_STAT_E2BIG,        /* Message too big */
  51         UCMB_STAT_ECRC,         /* CRC error */
  52 };
  53
  54
  55 static uint8_t ucmb_buf[sizeof(struct ucmb_message_hdr) +
  56                         UCMB_MAX_MSG_LEN +
  57                         sizeof(struct ucmb_message_footer)];
  58 static uint16_t ucmb_buf_ptr;
  59 static struct ucmb_status status_buf;
  60 static uint16_t ucmb_send_message_len;
  61
  62 /* Statemachine */
  63 static uint8_t ucmb_state;
  64 enum {
  65         UCMB_ST_LISTEN,
  66         UCMB_ST_SENDSTATUS,
  67         UCMB_ST_SENDMESSAGE,
  68 };
  69
  70 #define TRAILING        1
  71
  72
  73 static void ucmb_send_next_byte(void)
  74 {
  75         switch (ucmb_state) {
  76         case UCMB_ST_SENDSTATUS: {
  77                 const uint8_t *st = (const uint8_t *)&status_buf;
  78
  79                 if (ucmb_buf_ptr < sizeof(struct ucmb_status))
  80                         SPDR = st[ucmb_buf_ptr];
  81                 ucmb_buf_ptr++;
  82                 if (ucmb_buf_ptr == sizeof(struct ucmb_status) + TRAILING) {
  83                         ucmb_buf_ptr = 0;
  84                         if (ucmb_send_message_len) {
  85                                 ucmb_state = UCMB_ST_SENDMESSAGE;
  86                                 goto st_sendmessage;
  87                         } else
  88                                 ucmb_state = UCMB_ST_LISTEN;
  89                 }
  90                 break;
  91         }
  92         case UCMB_ST_SENDMESSAGE: {
  93   st_sendmessage:;
  94                 uint16_t full_length = sizeof(struct ucmb_message_hdr) +
  95                                        ucmb_send_message_len +
  96                                        sizeof(struct ucmb_message_footer);
  97                 if (ucmb_buf_ptr < full_length)
  98                         SPDR = ucmb_buf[ucmb_buf_ptr];
  99                 ucmb_buf_ptr++;
 100                 if (ucmb_buf_ptr == full_length + TRAILING) {
 101                         ucmb_send_message_len = 0;
 102                         ucmb_buf_ptr = 0;
 103                         ucmb_state = UCMB_ST_LISTEN;//FIXME retr status
 104                 }
 105                 break;
 106         } }
 107 }
 108
 109 static uint16_t crc16_block_update(uint16_t crc, const void *_data, uint16_t size)
 110 {
 111         const uint8_t *data = _data;
 112
 113         while (size) {
 114                 crc = _crc16_update(crc, *data);
 115                 data++;
 116                 size--;
 117         }
 118
 119         return crc;
 120 }
 121
 122 static uint16_t ucmb_calc_msg_buffer_crc(void)
 123 {
 124         const struct ucmb_message_hdr *hdr;
 125         uint16_t crc = 0xFFFF;
 126
 127         hdr = (const struct ucmb_message_hdr *)ucmb_buf;
 128         crc = crc16_block_update(crc, ucmb_buf,
 129                                  sizeof(struct ucmb_message_hdr) + hdr->len);
 130         crc ^= 0xFFFF;
 131
 132         return crc;
 133 }
 134
 135 /* SPI data transfer interrupt. */
 136 ISR(SPI_STC_vect)
 137 {
 138         uint8_t data;
 139
 140         data = SPDR;
 141
 142         switch (ucmb_state) {
 143         case UCMB_ST_LISTEN: {
 144                 struct ucmb_message_hdr *hdr;
 145                 struct ucmb_message_footer *footer;
 146
 147                 ucmb_buf[ucmb_buf_ptr++] = data;
 148                 if (ucmb_buf_ptr < sizeof(struct ucmb_message_hdr))
 149                         return; /* Header RX not complete. */
 150                 hdr = (struct ucmb_message_hdr *)ucmb_buf;
 151                 if (ucmb_buf_ptr == sizeof(struct ucmb_message_hdr)) {
 152                         if (hdr->magic != UCMB_MAGIC) {
 153                                 /* Invalid magic! Reset. */
 154                                 ucmb_buf_ptr = 0;
 155                                 return;
 156                         }
 157                         if (hdr->len > UCMB_MAX_MSG_LEN) {
 158                                 /* Invalid length. */
 159                                 //FIXME don't interrupt, but poll len bytes and
 160                                 // send an immediate failure report
 161                                 ucmb_buf_ptr = 0;
 162                                 return;
 163                         }
 164                         return;
 165                 }
 166
 167                 if (ucmb_buf_ptr == sizeof(struct ucmb_message_hdr) +
 168                                     sizeof(struct ucmb_message_footer) +
 169                                     hdr->len) {
 170                         footer = (struct ucmb_message_footer *)(
 171                                         ucmb_buf + sizeof(struct ucmb_message_hdr) +
 172                                         hdr->len);
 173                         status_buf.magic = UCMB_MAGIC;
 174                         status_buf.code = UCMB_STAT_OK;
 175                         if (ucmb_calc_msg_buffer_crc() != footer->crc)
 176                                 status_buf.code = UCMB_STAT_ECRC;
 177                         ucmb_state = UCMB_ST_SENDSTATUS;
 178                         ucmb_buf_ptr = 0;
 179                         ucmb_send_next_byte();
 180
 181                         ucmb_send_message_len = ucmb_rx_message(
 182                                         ucmb_buf + sizeof(struct ucmb_message_hdr),
 183                                         hdr->len);
 184                         if (ucmb_send_message_len) {
 185                                 footer = (struct ucmb_message_footer *)(
 186                                                 ucmb_buf + sizeof(struct ucmb_message_hdr) +
 187                                                 ucmb_send_message_len);
 188
 189                                 hdr->magic = UCMB_MAGIC;
 190                                 hdr->len = ucmb_send_message_len;
 191                                 footer->crc = ucmb_calc_msg_buffer_crc();
 192                         }
 193                 }
 194                 break;
 195         }
 196         case UCMB_ST_SENDSTATUS:
 197         case UCMB_ST_SENDMESSAGE:
 198                 ucmb_send_next_byte();
 199                 break;
 200         }
 201 }
 202
 203 void ucmb_init(void)
 204 {
 205         ucmb_state = UCMB_ST_LISTEN;
 206
 207         /* SPI slave mode 0 with IRQ enabled. */
 208         DDRB |= (1 << 4/*MISO*/);
 209         DDRB &= ~((1 << 5/*SCK*/) | (1 << 3/*MOSI*/) | (1 << 2/*SS*/));
 210         SPCR = (1 << SPE) | (1 << SPIE) /*| (1 << CPOL) | (1 << CPHA)*/;
 211         (void)SPSR; /* clear state */
 212         (void)SPDR; /* clear state */
 213 }