SimpleWireInterface.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_WIRE_SIMPLE_WIRE_INTERFACE_H
#define ACE_WIRE_SIMPLE_WIRE_INTERFACE_H
 
#include <stdint.h>
#include <Arduino.h> // pinMode(), digitalWrite()
 
namespace ace_wire {
 
class SimpleWireInterface {
  public:
    explicit SimpleWireInterface(
        uint8_t dataPin, uint8_t clockPin, uint8_t delayMicros
    ) :
        mDataPin(dataPin),
        mClockPin(clockPin),
        mDelayMicros(delayMicros)
    {}
 
    void begin() const {
      digitalWrite(mClockPin, LOW);
      digitalWrite(mDataPin, LOW);
 
      // Begin with both lines in INPUT mode to passively go HIGH.
      clockHigh();
      dataHigh();
    }
 
    void end() const {
      clockHigh();
      dataHigh();
    }
 
    uint8_t beginTransmission(uint8_t addr) const {
      clockHigh();
      dataHigh();
 
      dataLow();
      clockLow();
 
      // Send I2C addr (7 bits) and the R/W bit set to "write" (0x00).
      uint8_t effectiveAddr = (addr << 1) | 0x00;
      uint8_t res = write(effectiveAddr);
      return res ^ 0x1;
    }
 
    uint8_t write(uint8_t data) const {
      for (uint8_t i = 0;  i < 8; ++i) {
        if (data & 0x80) {
          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;
    }
 
    uint8_t endTransmission(bool sendStop = true) const {
      // clock will always be LOW when this is called
      if (sendStop) {
        dataLow();
        clockHigh();
        dataHigh();
      }
 
      return 0;
    }
 
    uint8_t requestFrom(uint8_t addr, uint8_t quantity, bool sendStop = true) {
      mQuantity = quantity;
      mSendStop = sendStop;
 
      clockHigh();
      dataHigh();
 
      dataLow();
      clockLow();
 
      // Send I2C addr (7 bits) and the R/W bit set to "read" (0x01).
      uint8_t effectiveAddr = (addr << 1) | 0x01;
      uint8_t ack = write(effectiveAddr);
 
      return (ack == 1) ? quantity : 0;
    }
 
    uint8_t read() {
      // Caller should not call when mQuantity is 0, but guard against it.
      if (! mQuantity) return 0xff;
 
      // Read one byte
      dataHigh();
      uint8_t data = 0;
      for (uint8_t i = 0; i < 8; ++i) {
        clockHigh();
        data <<= 1;
        uint8_t bit = digitalRead(mDataPin);
        data |= (bit & 0x1);
        clockLow();
      }
 
      // Decrement quantity to determine if NACK or ACK should be sent.
      mQuantity--;
      if (mQuantity) {
        sendAck();
      } else {
        sendNack();
        if (mSendStop) {
          endTransmission();
        }
      }
 
      return data;
    }
 
    // Use default copy constructor and assignment operator.
    SimpleWireInterface(const SimpleWireInterface&) = default;
    SimpleWireInterface& operator=(const SimpleWireInterface&) = default;
 
  private:
    uint8_t readAck() const {
      // Go into INPUT mode, reusing dataHigh(), saving 10 flash bytes on AVR.
      dataHigh();
 
      // Set the clock HIGH, because the I2C protocol says that SDA will not
      // change when SCL is HIGH and we expect the slave to abide by that.
      clockHigh();
 
      uint8_t ack = digitalRead(mDataPin);
 
      // Device releases SDA upon falling edge of the 9th CLK.
      clockLow();
      return ack;
    }
 
    void sendAck() const {
      dataLow();
      clockHigh();
      clockLow();
    }
 
    void sendNack() const {
      dataHigh();
      clockHigh();
      clockLow();
    }
 
    void bitDelay() const { delayMicroseconds(mDelayMicros); }
 
    void clockHigh() const { pinMode(mClockPin, INPUT); bitDelay(); }
 
    void clockLow() const { pinMode(mClockPin, OUTPUT); bitDelay(); }
 
    void dataHigh() const { pinMode(mDataPin, INPUT); bitDelay(); }
 
    void dataLow() const { pinMode(mDataPin, OUTPUT); bitDelay(); }
 
  private:
    uint8_t const mDataPin;
    uint8_t const mClockPin;
    uint8_t const mDelayMicros;
    uint8_t mQuantity;
    bool mSendStop;
};
 
}
 
#endif