SimpleTmiInterface.h

/*
MIT License
 
Copyright (c) 2021 Brian T. Park
 
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.
*/
 
#ifndef ACE_TMI_SIMPLE_TMI_INTERFACE_H
#define ACE_TMI_SIMPLE_TMI_INTERFACE_H
 
#include <Arduino.h>
 
namespace ace_tmi {
 
class SimpleTmiInterface {
  public:
    explicit SimpleTmiInterface(
        uint8_t dioPin,
        uint8_t clkPin,
        uint8_t delayMicros
    ) :
        mDioPin(dioPin),
        mClkPin(clkPin),
        mDelayMicros(delayMicros)
    {}
 
    void begin() const {
      digitalWrite(mClkPin, LOW);
      digitalWrite(mDioPin, LOW);
 
      // Begin with both lines at HIGH.
      clockHigh();
      dataHigh();
    }
 
    void end() const {
      clockHigh();
      dataHigh();
    }
 
    void startCondition() const {
      clockHigh();
      dataHigh();
 
      dataLow();
      clockLow();
    }
 
    void stopCondition() const {
      // clock will always be LOW when this is called
      dataLow();
      clockHigh();
      dataHigh();
    }
 
    uint8_t sendByte(uint8_t data) const {
      for (uint8_t i = 0;  i < 8; ++i) {
        if (data & 0x1) {
          dataHigh();
        } else {
          dataLow();
        }
        clockHigh();
        // An extra bitDelay() here would make the HIGH and LOW states symmetric
        // in duration (if digitalWrite() is assumed to be infinitely fast,
        // which it is definitely not). But actual devices that I have tested
        // seem to support the absence of that extra delay. So let's ignore it
        // to make the transfer speed faster.
        clockLow();
        data >>= 1;
      }
 
      uint8_t ack = readAck();
      return ack ^ 0x1; // invert the 0 and 1
    }
 
    // Use default copy constructor and assignment operator.
    SimpleTmiInterface(const SimpleTmiInterface&) = default;
    SimpleTmiInterface& operator=(const SimpleTmiInterface&) = default;
 
  private:
    uint8_t readAck() const {
      // Go into INPUT mode, reusing dataHigh(), saving 10 flash bytes on AVR.
      dataHigh();
 
      // DIO is supposed to remain stable after CLK is set HIGH.
      clockHigh();
 
      uint8_t ack = digitalRead(mDioPin);
 
      // Device releases DIO upon falling edge of the 9th CLK.
      clockLow();
      return ack;
    }
 
    void bitDelay() const { delayMicroseconds(mDelayMicros); }
 
    void clockHigh() const { pinMode(mClkPin, INPUT); bitDelay(); }
 
    void clockLow() const { pinMode(mClkPin, OUTPUT); bitDelay(); }
 
    void dataHigh() const { pinMode(mDioPin, INPUT); bitDelay(); }
 
    void dataLow() const { pinMode(mDioPin, OUTPUT); bitDelay(); }
 
  private:
    uint8_t const mDioPin;
    uint8_t const mClkPin;
    uint8_t const mDelayMicros;
};
 
} // ace_tmi
 
#endif