File content as of revision 3:712bf8967b68:

// Code derived from a number of sources including:
// simonbarker on MBED
// The search code is a port of Jim Studt's Adruino One Wire lib
// Can handle multiple devices per pin
// Rob Dobson, 2015

#include "Onewire.h"

Onewire::Onewire(PinName oneBus):oneBus_(oneBus)
{    
}

void Onewire::writeBit(int bit) 
{
    bit = bit & 0x01;
    if (bit) 
    {
        // Write '1' bit
        oneBus_.output();
        oneBus_ = 0;
        wait_us(5);
        oneBus_.input();
        wait_us(60);
    }
    else
    {
        // Write '0' bit
        oneBus_.output();
        oneBus_ = 0;
        wait_us(70);
        oneBus_.input();
        wait_us(2);
    }
}

int Onewire::readBit() 
{
    char result;

    oneBus_.output();
    oneBus_ = 0;
    wait_us(1);
    oneBus_.input();
    wait_us(5);
    result = oneBus_.read();
    wait_us(55);
    return result;
}

int Onewire::init()
{
    oneBus_.output();
    oneBus_ = 0;
    wait_us(480);
    oneBus_.input();
    wait_us(60);
    if (oneBus_.read() == 0) 
    {
        wait(0.0001);
        return 1;
    }
    return 0;
}

int Onewire::readByte() 
{
    int result = 0;

    for (int loop = 0; loop < 8; loop++) {
        // shift the result to get it ready for the next bit
        result >>= 1;

        // if result is one, then set MS bit
        if (readBit())
            result |= 0x80;
    }
    return result;
}

void Onewire::writeByte(char data) 
{
    // Loop to write each bit in the byte, LS-bit first
    for (int loop = 0; loop < 8; loop++) {
        writeBit(data & 0x01);

        // shift the data byte for the next bit
        data >>= 1;
    }
}

unsigned char Onewire::CRC(unsigned char* addr, unsigned char len) 
{
    unsigned char i, j;
    unsigned char crc = 0;

    for (i = 0; i < len; i++) {
        unsigned char inbyte = addr[i];
        for (j = 0; j < 8; j++) {
            unsigned char mix = (crc ^ inbyte) & 0x01;
            crc >>= 1;
            if (mix) crc ^= 0x8C;
            inbyte >>= 1;
        }
    }
    return crc;
}

//
// You need to use this function to start a search again from the beginning.
// You do not need to do it for the first search, though you could.
//
void Onewire::reset_search()
{
    // reset the search state
    _search_LastDiscrepancy = 0;
    _search_LastDeviceFlag = false;
    _search_LastFamilyDiscrepancy = 0;
    for(int i = 7; i >= 0; i--) 
        _search_ROM_NO[i] = 0;
}

// Search Copied from Arduino code
//
// Perform a search. If this function returns a '1' then it has
// enumerated the next device and you may retrieve the ROM from the
// Onewire::address variable. If there are no devices, no further
// devices, or something horrible happens in the middle of the
// enumeration then a 0 is returned.  If a new device is found then
// its address is copied to newAddr.  Use Onewire::reset_search() to
// start over.
//
// --- Replaced by the one from the Dallas Semiconductor web site ---
//--------------------------------------------------------------------------
// Perform the 1-Wire Search Algorithm on the 1-Wire bus using the existing
// search state.
// Return TRUE  : device found, ROM number in ROM_NO buffer
//        FALSE : device not found, end of search
//
uint8_t Onewire::search(uint8_t *newAddr)
{
   uint8_t id_bit_number = 1;
   uint8_t last_zero = 0, rom_byte_number = 0, search_result = 0;
   uint8_t id_bit = 0, cmp_id_bit = 0;

   // initialize for search
   unsigned char rom_byte_mask = 1, search_direction = 0;

   // if the last call was not the last one
   if (!_search_LastDeviceFlag)
   {
      // 1-Wire reset
      if (!init())
      {
         // reset the search
         _search_LastDiscrepancy = 0;
         _search_LastDeviceFlag = false;
         _search_LastFamilyDiscrepancy = 0;
         return false;
      }

      // issue the search command
      writeByte(0xF0);

      // loop to do the search
      do
      {
         // read a bit and its complement
         id_bit = readBit();
         cmp_id_bit = readBit();

         // check for no devices on 1-wire
         if ((id_bit == 1) && (cmp_id_bit == 1))
            break;
         else
         {
            // all devices coupled have 0 or 1
            if (id_bit != cmp_id_bit)
               search_direction = id_bit;  // bit write value for search
            else
            {
               // if this discrepancy if before the Last Discrepancy
               // on a previous next then pick the same as last time
               if (id_bit_number < _search_LastDiscrepancy)
                  search_direction = ((_search_ROM_NO[rom_byte_number] & rom_byte_mask) > 0);
               else
                  // if equal to last pick 1, if not then pick 0
                  search_direction = (id_bit_number == _search_LastDiscrepancy);

               // if 0 was picked then record its position in LastZero
               if (search_direction == 0)
               {
                  last_zero = id_bit_number;

                  // check for Last discrepancy in family
                  if (last_zero < 9)
                     _search_LastFamilyDiscrepancy = last_zero;
               }
            }

            // set or clear the bit in the ROM byte rom_byte_number
            // with mask rom_byte_mask
            if (search_direction == 1)
              _search_ROM_NO[rom_byte_number] |= rom_byte_mask;
            else
              _search_ROM_NO[rom_byte_number] &= ~rom_byte_mask;

            // serial number search direction write bit
            writeBit(search_direction);

            // increment the byte counter id_bit_number
            // and shift the mask rom_byte_mask
            id_bit_number++;
            rom_byte_mask <<= 1;

            // if the mask is 0 then go to new SerialNum byte rom_byte_number and reset mask
            if (rom_byte_mask == 0)
            {
                rom_byte_number++;
                rom_byte_mask = 1;
            }
         }
      }
      while(rom_byte_number < 8);  // loop until through all ROM bytes 0-7

      // if the search was successful then
      if (!(id_bit_number < 65))
      {
         // search successful so set LastDiscrepancy,LastDeviceFlag,search_result
         _search_LastDiscrepancy = last_zero;

         // check for last device
         if (_search_LastDiscrepancy == 0)
            _search_LastDeviceFlag = true;

         search_result = true;
      }
   }

   // if no device found then reset counters so next 'search' will be like a first
   if (!search_result || !_search_ROM_NO[0])
   {
      _search_LastDiscrepancy = 0;
      _search_LastDeviceFlag = false;
      _search_LastFamilyDiscrepancy = 0;
      search_result = false;
   }
   for (int i = 0; i < 8; i++)
       newAddr[i] = _search_ROM_NO[i];
   return search_result;
  }