Erik - / SoftI2C

A software I2C interface which is a drop-in replacement for the regular mbed I2C interface in case you run out of I2C ports

Dependents:   Luminocity laser-tag

This is a first version. Doesn't mean more versions will come, mainly means it may be a bit buggy. If it does not work for you: first try exactly the same code with the regular hardware I2C. If that does work, well then I made an error somewhere :D. You can send me a message if you can't figure it out, although without your hardware it generally is hard for me to reproduce.

While basic I2C should work, advanced things like clock stretching and multi-master I2C busses are not supported.

If you find an error and solve it: Send a pull request and I generally will accept it :).

SoftI2C.cpp

Committer:
Sissors
Date:
2016-11-28
Revision:
1:05473196d133
Parent:
0:fee70b6fe0e9

File content as of revision 1:05473196d133:

#include "SoftI2C.h"

SoftI2C::SoftI2C(PinName sda, PinName scl) : _sda(sda), _scl(scl) {
    // Set defaults
    _sda.mode(PullNone);
    _scl.mode(PullNone);
    _sda.input();
    _scl.input();
    frequency(100000);
    
    active = false;
    
    }
    
void SoftI2C::frequency(int hz) {
    delay_us = 1000000 / hz / 4; //delay is a quarter of the total period
}

int SoftI2C::read(int address, char *data, int length, bool repeated) {
    start();
    
    // Write address with LSB to one
    if (write(address | 0x01) == 0) {
        return 1;
    }  
    
    // Read the data
    for(int i = 0; i<length - 1; i++) {
        data[i] = read(1);
    }
    data[length-1] = read(0);
    
    if (repeated == false) {
        stop();
    }
    return 0;
}

int SoftI2C::write(int address, const char *data, int length, bool repeated) {
    start();
    
    // Write address with LSB to zero
    if (write(address & 0xFE) == 0) {
        return 1;
    }  
    
    // Write the data
    for(int i = 0; i<length; i++) {
        if(write(data[i]) == 0) {
            return 1;
        }
    }
    
    if (repeated == false) {
        stop();
    }
    return 0;
}

int SoftI2C::read(int ack) {
    int retval = 0;
    _scl.output();
    
    // Shift the bits out, msb first
    for (int i = 7; i>=0; i--) {
        //SCL low
        _scl.write(0);
        _sda.input();
        wait_us(delay_us);
        
        //read SDA
        retval |= _sda.read() << i;
        wait_us(delay_us);
        
        //SCL high again
        _scl.write(1);
        wait_us(delay_us << 1); //wait two delays
    }
    
    // Last cycle to set the ACK
    _scl.write(0);
    if ( ack ) {
        _sda.output();
        _sda.write(0);
    } else {
        _sda.input();
    }
    wait_us(delay_us << 1);
    
    _scl.write(1);
    wait_us(delay_us << 1);

    
    return retval;
}

int SoftI2C::write(int data) {
     _scl.output();
     
    // Shift the bits out, msb first
    for (int i = 7; i>=0; i--) {
        //SCL low
        _scl.write(0);
        wait_us(delay_us);
        
        //Change SDA depending on the bit
        if ( (data >> i) & 0x01 ) {
            _sda.input();
        } else {
            _sda.output();
            _sda.write(0);
        }
        wait_us(delay_us);
        
        //SCL high again
        _scl.write(1);
        wait_us(delay_us << 1); //wait two delays
    }
    
    // Last cycle to get the ACK
    _scl.write(0);
    wait_us(delay_us);
    
    _sda.input();
    wait_us(delay_us);
    
    _scl.write(1);
    wait_us(delay_us);
    int retval = ~_sda.read(); //Read the ack
    wait_us(delay_us);
    
    return retval;
}

void SoftI2C::start(void) {
    if (active) { //if repeated start
        //Set SDA high, toggle scl
        _sda.input();
        _scl.output();
        _scl.write(0);
        wait_us(delay_us << 1);
        _scl.write(1);
        wait_us(delay_us << 1);
    }
    // Pull SDA low
    _sda.output();
    _sda.write(0);
    wait_us(delay_us);
    active = true;
}

void SoftI2C::stop(void) {
    // Float SDA high
    _scl.output();
    _scl.write(0);
    _sda.output();
    _sda.write(0);
    wait_us(delay_us);
    _scl.input();
    wait_us(delay_us);
    _sda.input();
    wait_us(delay_us);
    
    active = false;
}