source: rtos_arduino/trunk/arduino_lib/libraries/Bridge/src/Bridge.cpp@ 136

/*
  Copyright (c) 2013 Arduino LLC. All right reserved.

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public
  License along with this library; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/

#include "Bridge.h"

BridgeClass::BridgeClass(Stream &_stream) :
  index(0), stream(_stream), started(false), max_retries(0) {
  // Empty
}

void BridgeClass::begin() {
  if (started)
    return;
  started = true;

  // Wait for U-boot to finish startup
  do {
    dropAll();
    delay(1000);
  } while (stream.available() > 0);

  while (true) {
    // Bridge interrupt:
    // - Ask the bridge to close itself
    uint8_t quit_cmd[] = {'X', 'X', 'X', 'X', 'X'};
    max_retries = 1;
    transfer(quit_cmd, 5);

    // Bridge startup:
    // - If the bridge is not running starts it safely
    stream.print(CTRL_C);
    delay(250);
    stream.print(F("\n"));
    delay(250);
    stream.print(F("\n"));
    delay(500);
    // Wait for OpenWRT message
    // "Press enter to activate console"
    stream.print(F("run-bridge\n"));
    delay(500);
    dropAll();

    // Reset the brigde to check if it is running
    uint8_t cmd[] = {'X', 'X', '1', '0', '0'};
    uint8_t res[4];
    max_retries = 50;
    uint16_t l = transfer(cmd, 5, res, 4);
    if (l == TRANSFER_TIMEOUT) {
      // Bridge didn't start...
      // Maybe the board is starting-up?

      // Wait and retry
      delay(1000);
      continue;
    }
    if (res[0] != 0)
      while (true);

    // Detect bridge version
    if (l == 4) {
      bridgeVersion = (res[1]-'0')*100 + (res[2]-'0')*10 + (res[3]-'0');
    } else {
      // Bridge v1.0.0 didn't send any version info
      bridgeVersion = 100;
    }

    max_retries = 50;
    return;
  }
}

void BridgeClass::put(const char *key, const char *value) {
  // TODO: do it in a more efficient way
  String cmd = "D";
  cmd += key;
  cmd += "\xFE";
  cmd += value;
  transfer((uint8_t*)cmd.c_str(), cmd.length());
}

unsigned int BridgeClass::get(const char *key, uint8_t *value, unsigned int maxlen) {
  uint8_t cmd[] = {'d'};
  unsigned int l = transfer(cmd, 1, (uint8_t *)key, strlen(key), value, maxlen);
  if (l < maxlen)
    value[l] = 0; // Zero-terminate string
  return l;
}

#if defined(ARDUINO_ARCH_AVR)
// AVR use an optimized implementation of CRC
#include <util/crc16.h>
#else
// Generic implementation for non-AVR architectures
uint16_t _crc_ccitt_update(uint16_t crc, uint8_t data)
{
  data ^= crc & 0xff;
  data ^= data << 4;
  return ((((uint16_t)data << 8) | ((crc >> 8) & 0xff)) ^
          (uint8_t)(data >> 4) ^
          ((uint16_t)data << 3));
}
#endif

void BridgeClass::crcUpdate(uint8_t c) {
  CRC = _crc_ccitt_update(CRC, c);
}

void BridgeClass::crcReset() {
  CRC = 0xFFFF;
}

void BridgeClass::crcWrite() {
  stream.write((char)(CRC >> 8));
  stream.write((char)(CRC & 0xFF));
}

bool BridgeClass::crcCheck(uint16_t _CRC) {
  return CRC == _CRC;
}

uint16_t BridgeClass::transfer(const uint8_t *buff1, uint16_t len1,
                               const uint8_t *buff2, uint16_t len2,
                               const uint8_t *buff3, uint16_t len3,
                               uint8_t *rxbuff, uint16_t rxlen)
{
  uint16_t len = len1 + len2 + len3;
  uint8_t retries = 0;
  for ( ; retries < max_retries; retries++, delay(100), dropAll() /* Delay for retransmission */) {
    // Send packet
    crcReset();
    stream.write((char)0xFF);                // Start of packet (0xFF)
    crcUpdate(0xFF);
    stream.write((char)index);               // Message index
    crcUpdate(index);
    stream.write((char)((len >> 8) & 0xFF)); // Message length (hi)
    crcUpdate((len >> 8) & 0xFF);
    stream.write((char)(len & 0xFF));        // Message length (lo)
    crcUpdate(len & 0xFF);
    for (uint16_t i = 0; i < len1; i++) { // Payload
      stream.write((char)buff1[i]);
      crcUpdate(buff1[i]);
    }
    for (uint16_t i = 0; i < len2; i++) { // Payload
      stream.write((char)buff2[i]);
      crcUpdate(buff2[i]);
    }
    for (uint16_t i = 0; i < len3; i++) { // Payload
      stream.write((char)buff3[i]);
      crcUpdate(buff3[i]);
    }
    crcWrite();                     // CRC

    // Wait for ACK in 100ms
    if (timedRead(100) != 0xFF)
      continue;
    crcReset();
    crcUpdate(0xFF);

    // Check packet index
    if (timedRead(5) != index)
      continue;
    crcUpdate(index);

    // Recv len
    int lh = timedRead(10);
    if (lh < 0)
      continue;
    crcUpdate(lh);
    int ll = timedRead(10);
    if (ll < 0)
      continue;
    crcUpdate(ll);
    uint16_t l = lh;
    l <<= 8;
    l += ll;

    // Recv data
    for (uint16_t i = 0; i < l; i++) {
      int c = timedRead(5);
      if (c < 0)
        continue;
      // Cut received data if rxbuffer is too small
      if (i < rxlen)
        rxbuff[i] = c;
      crcUpdate(c);
    }

    // Check CRC
    int crc_hi = timedRead(5);
    if (crc_hi < 0)
      continue;
    int crc_lo = timedRead(5);
    if (crc_lo < 0)
      continue;
    if (!crcCheck((crc_hi << 8) + crc_lo))
      continue;

    // Increase index
    index++;

    // Return bytes received
    if (l > rxlen)
      return rxlen;
    return l;
  }

  // Max retries exceeded
  return TRANSFER_TIMEOUT;
}

int BridgeClass::timedRead(unsigned int timeout) {
  int c;
  unsigned long _startMillis = millis();
  do {
    c = stream.read();
    if (c >= 0) return c;
  } while (millis() - _startMillis < timeout);
  return -1;     // -1 indicates timeout
}

void BridgeClass::dropAll() {
  while (stream.available() > 0) {
    stream.read();
  }
}

// Bridge instance
#ifdef __AVR_ATmega32U4__
// Leonardo variants (where HardwareSerial is Serial1)
SerialBridgeClass Bridge(Serial1);
#else
SerialBridgeClass Bridge(Serial);
#endif