i2c.cpp

#include "mraa.hpp"
#include <cassert>
#include <csignal>
#include <iostream>

#define SHIELD_I2C_ADDR 0x40

#define MS 1000

uint8_t registers[] = {
  6,   // output 0
  10,  // output 1
  14,  // output 2
  18,  // output 3
  22,  // output 4
  26,  // output 5
  30,  // output 6
  34,  // output 7
  38,  // output 8
  42,  // output 9
  46,  // output 10
  50,  // output 11
  54,  // output 12
  58,  // output 13
  62,  // output 14
  66   // output 15
};
  


void initPWM(mraa::I2c *i2c) {
  uint8_t writeBuf[2] = {0};
  writeBuf[0] = 0x00; // Write to MODE 1 Register;
  writeBuf[1] = 1 << 4; // Enable Sleep Mode
 
  i2c->address(SHIELD_I2C_ADDR);
  i2c->write(writeBuf, 2);
 
  usleep(10 * MS);

  writeBuf[0] = 0xFE; // Write Prescaler Register
  writeBuf[1] = 0xA3; // Set pwm frequency to ~40 Hz

  i2c->address(SHIELD_I2C_ADDR);
  i2c->write(writeBuf, 2);
  
  writeBuf[0] = 0; // Write to the MODE 1 register
  writeBuf[1] = 1 << 5 // Enable auto increment mode
	    | 0 << 4; // Enable the oscillator
        
  i2c->address(SHIELD_I2C_ADDR);
  i2c->write(writeBuf, 2);
}


void writePWM(mraa::I2c* i2c, int index, double duty) {
  assert(0.0 <= duty && duty <= 1.0);
  assert(0 <= index && index < 16);
  double on = 4095.0 * duty;
  uint16_t onRounded = (uint16_t) on;

  uint8_t writeBuf[5];

  // ON_L
  writeBuf[0] = registers[index];
  writeBuf[1] = 0x00; // ON LSB
  writeBuf[2] = 0x00; // ON MSB
  writeBuf[3] = onRounded & 0xFF; // OFF LSB
  writeBuf[4] = (onRounded >> 8) & 0xFF; // OFF MSB
  i2c->address(SHIELD_I2C_ADDR);
  i2c->write(writeBuf, 5);
}