File content as of revision 11:bc8ed7280966:

/*
Copyright (c) 2007, Jim Studt  (original old version - many contributors since)

The latest version of this library may be found at:
  http://www.pjrc.com/teensy/td_libs_Onehtml

OneWire has been maintained by Paul Stoffregen (paul@pjrc.com) since
January 2010.  At the time, it was in need of many bug fixes, but had
been abandoned the original author (Jim Studt).  None of the known
contributors were interested in maintaining One  Paul typically
works on OneWire every 6 to 12 months.  Patches usually wait that
long.  If anyone is interested in more actively maintaining OneWire,
please contact Paul.

Version 2.2:
  Teensy 3.0 compatibility, Paul Stoffregen, paul@pjrc.com
  Arduino Due compatibility, http://arduino.cc/forum/index.php?topic=141030
  Fix DS18B20 example negative temperature
  Fix DS18B20 example's low res modes, Ken Butcher
  Improve reset timing, Mark Tillotson
  Add const qualifiers, Bertrik Sikken
  Add initial value input to crc16, Bertrik Sikken
  Add target_search() function, Scott Roberts

Version 2.1:
  Arduino 1.0 compatibility, Paul Stoffregen
  Improve temperature example, Paul Stoffregen
  DS250x_PROM example, Guillermo Lovato
  PIC32 (chipKit) compatibility, Jason Dangel, dangel.jason AT gmail.com
  Improvements from Glenn Trewitt:
  - crc16() now works
  - check_crc16() does all of calculation/checking work.
  - Added read_bytes() and write_bytes(), to reduce tedious loops.
  - Added ds2408 example.
  Delete very old, out-of-date readme file (info is here)

Version 2.0: Modifications by Paul Stoffregen, January 2010:
http://www.pjrc.com/teensy/td_libs_Onehtml
  Search fix from Robin James
    http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1238032295/27#27
  Use direct optimized I/O in all cases
  Disable interrupts during timing critical sections
    (this solves many random communication errors)
  Disable interrupts during read-modify-write I/O
  Reduce RAM consumption by eliminating unnecessary
    variables and trimming many to 8 bits
  Optimize both crc8 - table version moved to flash

Modified to work with larger numbers of devices - avoids loop.
Tested in Arduino 11 alpha with 12 sensors.
26 Sept 2008 -- Robin James
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1238032295/27#27

Updated to work with arduino-0008 and to include skip() as of
2007/07/06. --RJL20

Modified to calculate the 8-bit CRC directly, avoiding the need for
the 256-byte lookup table to be loaded in RAM.  Tested in arduino-0010
-- Tom Pollard, Jan 23, 2008

Jim Studt's original library was modified by Josh Larios.

Tom Pollard, pollard@alum.mit.edu, contributed around May 20, 2008

Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Much of the code was inspired by Derek Yerger's code, though I don't
think much of that remains.  In any event that was..
    (copyleft) 2006 by Derek Yerger - Free to distribute freely.

The CRC code was excerpted and inspired by the Dallas Semiconductor
sample code bearing this copyright.
//---------------------------------------------------------------------------
// Copyright (C) 2000 Dallas Semiconductor Corporation, All Rights Reserved.
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation
// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY,  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
// IN NO EVENT SHALL DALLAS SEMICONDUCTOR BE LIABLE FOR ANY CLAIM, DAMAGES
// OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
// OTHER DEALINGS IN THE SOFTWARE.
//
// Except as contained in this notice, the name of Dallas Semiconductor
// shall not be used except as stated in the Dallas Semiconductor
// Branding Policy.
//--------------------------------------------------------------------------
*/
#include "OneWire.h"

/**
 * @brief   Constructs a OneWire object.
 * @note    GPIO is configured as output and an internal pull up resistor is connected.
 *          But because for STM chips it takes very long time to change from output
 *          to input an open drain mode is used rather and the GPIO remains output forever.
 * @param
 * @retval
 */
OneWire::OneWire(PinName pin) :
    DigitalInOut(pin)
{
    MODE(); // set mode either PullUp or OpenDrain for STM
#if ONEWIRE_SEARCH
    reset_search();
#endif
}

/**
 * @brief   Performs the onewire reset function.
 * @note    We will wait up to 250uS for the bus to come high, 
 *          if it doesn't then it is broken or shorted and we return a 0;
 * @param
 * @retval  1 if a device asserted a presence pulse, 0 otherwise.
 */
uint8_t OneWire::reset(void)
{
    uint8_t r;
    uint8_t retries = 125;

    INPUT();
    // wait until the wire is high... just in case
    do {
        if (--retries == 0)
            return 0;
        wait_us(2);
    } while (READ() == 0);

    OUTPUT();
    WRITE(0);
    wait_us(480);
    INPUT();
    wait_us(65);
    r = !READ();
    wait_us(420);
    return r;
}

/**
 * @brief   Writes a bit.
 * @note    GPIO registers are used for STM chips to cut time.
 * @param
 * @retval
 */
void OneWire::write_bit(uint8_t v)
{
    OUTPUT();
    if (v & 1) {
        WRITE(0);   // drive output low
        wait_us(1);
        WRITE(1);   // drive output high
        wait_us(60);
    }
    else {
        WRITE(0);   // drive output low
        wait_us(60);
        WRITE(1);   // drive output high
        wait_us(1);
    }
}

/**
 * @brief   Reads a bit.
 * @note    GPIO registers are used for STM chips to cut time.
 * @param
 * @retval
 */
uint8_t OneWire::read_bit(void)
{
    uint8_t r;
    int     t;

    OUTPUT();
    timer.start();
    WRITE(0);
    INPUT();
    t = timer.read_us();
    if (t < 7)
        wait_us(7 - t);
    r = READ();
    timer.stop();
    timer.reset();
    wait_us(55);
    return r;
}

/**
 * @brief   Writes a byte.
 * @note    The writing code uses the active drivers to raise the
            pin high, if you need power after the write (e.g. DS18S20 in
            parasite power mode) then set 'power' to 1, otherwise the pin will
            go tri-state at the end of the write to avoid heating in a short or
            other mishap.
 * @param
 * @retval
 */
void OneWire::write_byte(uint8_t v, uint8_t power /* = 0 */ )
{
    uint8_t bitMask;

    for (bitMask = 0x01; bitMask; bitMask <<= 1)
        write_bit((bitMask & v) ? 1 : 0);
    if (!power)
        INPUT();
}

/**
 * @brief   Writes bytes.
 * @note
 * @param
 * @retval
 */
void OneWire::write_bytes(const uint8_t* buf, uint16_t count, bool power /* = 0 */ )
{
    for (uint16_t i = 0; i < count; i++)
        write_byte(buf[i]);
    if (!power)
        INPUT();
}

/**
 * @brief   Reads a byte.
 * @note
 * @param
 * @retval
 */
uint8_t OneWire::read_byte()
{
    uint8_t bitMask;
    uint8_t r = 0;

    for (bitMask = 0x01; bitMask; bitMask <<= 1) {
        if (read_bit())
            r |= bitMask;
    }

    return r;
}

/**
 * @brief   Reads bytes.
 * @note
 * @param
 * @retval
 */
void OneWire::read_bytes(uint8_t* buf, uint16_t count)
{
    for (uint16_t i = 0; i < count; i++)
        buf[i] = read_byte();
}

/**
 * @brief   Selects ROM.
 * @note
 * @param
 * @retval
 */
void OneWire::select(const uint8_t rom[8])
{
    uint8_t i;

    write_byte(0x55);   // Choose ROM
    for (i = 0; i < 8; i++)
        write_byte(rom[i]);
}

/**
 * @brief   Skips ROM select.
 * @note
 * @param
 * @retval
 */
void OneWire::skip()
{
    write_byte(0xCC);   // Skip ROM
}

/**
 * @brief   Unpowers the chip.
 * @note
 * @param
 * @retval
 */
void OneWire::depower()
{
    INPUT();
}

#if ONEWIRE_SEARCH
//

/**
 * @brief   Resets the search state.
 * @note    We need to use this function to start a search again from the beginning.
 *          We do not need to do it for the first search, though we could.
 * @param
 * @retval
 */
void OneWire::reset_search()
{
    // reset the search state
    LastDiscrepancy = 0;
    LastDeviceFlag = false;
    LastFamilyDiscrepancy = 0;
    for (int i = 7;; i--) {
        ROM_NO[i] = 0;
        if (i == 0)
            break;
    }
}

/**
 * @brief   Sets the search state to find SearchFamily type devices.
 * @note
 * @param
 * @retval
 */
void OneWire::target_search(uint8_t family_code)
{
    // set the search state to find SearchFamily type devices
    ROM_NO[0] = family_code;
    for (uint8_t i = 1; i < 8; i++)
        ROM_NO[i] = 0;
    LastDiscrepancy = 64;
    LastFamilyDiscrepancy = 0;
    LastDeviceFlag = false;
}

/**
 * @brief   Performs a search.
 * @note    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.
 * @param
 * @retval  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;
    uint8_t         last_zero, rom_byte_number, search_result;
    uint8_t         id_bit, cmp_id_bit;

    unsigned char   rom_byte_mask, search_direction;

    // initialize for search
    id_bit_number = 1;
    last_zero = 0;
    rom_byte_number = 0;
    rom_byte_mask = 1;
    search_result = 0;

    // if the last call was not the last one
    if (!LastDeviceFlag) {
        // 1-Wire reset
        if (!reset()) {
            // reset the search
            LastDiscrepancy = 0;
            LastDeviceFlag = false;
            LastFamilyDiscrepancy = 0;
            return false;
        }

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

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

            // 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 < LastDiscrepancy)
                        search_direction = ((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 == 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)
                            LastFamilyDiscrepancy = last_zero;
                    }
                }

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

                // serial number search direction write bit
                write_bit(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
            LastDiscrepancy = last_zero;

            // check for last device
            if (LastDiscrepancy == 0)
                LastDeviceFlag = true;

            search_result = true;
        }
    }

    // if no device found then reset counters so next 'search' will be like a first
    if (!search_result || !ROM_NO[0]) {
        LastDiscrepancy = 0;
        LastDeviceFlag = false;
        LastFamilyDiscrepancy = 0;
        search_result = false;
    }

    for (int i = 0; i < 8; i++)
        newAddr[i] = ROM_NO[i];
    return search_result;
}
#endif
//
#if ONEWIRE_CRC
//
/**
 * @brief   Computes a Dallas Semiconductor 8 bit CRC directly.
 * @note    The 1-Wire CRC scheme is described in Maxim Application Note 27:
            "Understanding and Using Cyclic Redundancy Checks with Maxim iButton Products"
 * @param
 * @retval
 */
uint8_t OneWire::crc8(const uint8_t* addr, uint8_t len)
{
    uint8_t crc = 0;

    while (len--) {
        uint8_t inbyte = *addr++;
        for (uint8_t i = 8; i; i--) {
            uint8_t mix = (crc ^ inbyte) & 0x01;
            crc >>= 1;
            if (mix)
                crc ^= 0x8C;
            inbyte >>= 1;
        }
    }

    return crc;
}
#endif