microbit-dal/source/MicroBitI2C.cpp

#include "mbed.h"
#include "MicroBit.h"
#include "twi_master.h"
#include "nrf_delay.h"

/**
  * Constructor. 
  * Create an instance of i2c
  * @param sda the Pin to be used for SDA
  * @param scl the Pin to be used for SCL
  * Example:
  * @code 
  * MicroBitI2C i2c(MICROBIT_PIN_SDA, MICROBIT_PIN_SCL);
  * @endcode
  * @note this should prevent i2c lockups as well.
  */
MicroBitI2C::MicroBitI2C(PinName sda, PinName scl) : I2C(sda,scl)
{
    this->retries = 0;
}

/**
 * Performs a complete read transaction. The bottom bit of the address is forced to 1 to indicate a read.
 *
 * @address 8-bit I2C slave address [ addr | 1 ]
 * @data Pointer to the byte-array to read data in to
 * @length Number of bytes to read
 * @repeated Repeated start, true - don't send stop at end.
 *
 * @return MICROBIT_OK on success, MICROBIT_I2C_ERROR if an unresolved read failure is detected.
 */
int MicroBitI2C::read(int address, char *data, int length, bool repeated)
{
    int result = I2C::read(address,data,length,repeated);
    
    //0 indicates a success, presume failure
    while(result != 0 && retries < MICROBIT_I2C_MAX_RETRIES)
    {
        _i2c.i2c->EVENTS_ERROR = 0;
        _i2c.i2c->ENABLE       = TWI_ENABLE_ENABLE_Disabled << TWI_ENABLE_ENABLE_Pos; 
        _i2c.i2c->POWER        = 0;
        nrf_delay_us(5);
        _i2c.i2c->POWER        = 1;
        _i2c.i2c->ENABLE       = TWI_ENABLE_ENABLE_Enabled << TWI_ENABLE_ENABLE_Pos;
        twi_master_init_and_clear();
        result = I2C::read(address,data,length,repeated);
        retries++;
    }
    
    if(result != 0)
        return MICROBIT_I2C_ERROR;
   
    retries = 0; 
    return MICROBIT_OK;
}

/**
 * Performs a complete write transaction. The bottom bit of the address is forced to 0 to indicate a write.
 *
 * @address 8-bit I2C slave address [ addr | 0 ]
 * @data Pointer to the byte-arraycontaining the data to write 
 * @length Number of bytes to write
 * @repeated Repeated start, true - don't send stop at end.
 *
 * @return MICROBIT_OK on success, MICROBIT_I2C_ERROR if an unresolved write failure is detected.
 */
int MicroBitI2C::write(int address, const char *data, int length, bool repeated)
{   
    int result = I2C::write(address,data,length,repeated);
    
    //0 indicates a success, presume failure
    while(result != 0 && retries < MICROBIT_I2C_MAX_RETRIES)
    {
        _i2c.i2c->EVENTS_ERROR = 0;
        _i2c.i2c->ENABLE       = TWI_ENABLE_ENABLE_Disabled << TWI_ENABLE_ENABLE_Pos; 
        _i2c.i2c->POWER        = 0;
        nrf_delay_us(5);
        _i2c.i2c->POWER        = 1;
        _i2c.i2c->ENABLE       = TWI_ENABLE_ENABLE_Enabled << TWI_ENABLE_ENABLE_Pos;
        
        twi_master_init_and_clear();
        result = I2C::write(address,data,length,repeated);
        retries++;
    }
    
    if(result != 0)
        return MICROBIT_I2C_ERROR;
        
    retries = 0; 
    return MICROBIT_OK;
}