ps2dev.cpp

/*
 * ps2dev.cpp - an interface library for ps2 host.  
 * limitations:
 *      we do not handle parity errors.
 *      The timing constants are hard coded from the spec. Data rate is
 *         not impressive.
 *      probably lots of room for optimization.
 */

//#include "WProgram.h"
#include "Arduino.h"
#include "ps2dev.h"


//since for the device side we are going to be in charge of the clock,
//the two defines below are how long each _phase_ of the clock cycle is
#define CLKFULL 40
// we make changes in the middle of a phase, this how long from the
// start of phase to the when we drive the data line
#define CLKHALF 20

/*
 * the clock and data pins can be wired directly to the clk and data pins
 * of the PS2 connector.  No external parts are needed.
 */
PS2dev::PS2dev(int clk, int data)
{
  _ps2clk = clk;
  _ps2data = data;
  gohi(_ps2clk);
  gohi(_ps2data);
}

/*
 * according to some code I saw, these functions will
 * correctly set the clock and data pins for
 * various conditions.  It's done this way so you don't need
 * pullup resistors.
 */
void
PS2dev::gohi(int pin)
{
  pinMode(pin, INPUT);
  digitalWrite(pin, HIGH);
}

void
PS2dev::golo(int pin)
{
  pinMode(pin, OUTPUT);
  digitalWrite(pin, LOW);
}

int PS2dev::write(unsigned char data)
{
  unsigned char i;
  unsigned char parity = 1;

  //	Serial.print("sending ");
  //Serial.println(data,HEX);

	
  if (digitalRead(_ps2clk) == LOW) {
    return -1;
  }

  if (digitalRead(_ps2data) == LOW) {
    return -2;
  }


  golo(_ps2data);
  delayMicroseconds(CLKHALF);
  // device sends on falling clock
  golo(_ps2clk);	// start bit
  delayMicroseconds(CLKFULL);
  gohi(_ps2clk);
  delayMicroseconds(CLKHALF);

  for (i=0; i < 8; i++)
    {
      if (data & 0x01)
	{
	  gohi(_ps2data);
	} else {
	golo(_ps2data);
      }
      delayMicroseconds(CLKHALF);
      golo(_ps2clk);	
      delayMicroseconds(CLKFULL);
      gohi(_ps2clk);
      delayMicroseconds(CLKHALF);

      parity = parity ^ (data & 0x01);
      data = data >> 1;
    }
  // parity bit
  if (parity)
    {
      gohi(_ps2data);
    } else {
    golo(_ps2data);
  }
  delayMicroseconds(CLKHALF);
  golo(_ps2clk);	
  delayMicroseconds(CLKFULL);
  gohi(_ps2clk);
  delayMicroseconds(CLKHALF);

  // stop bit
  gohi(_ps2data);
  delayMicroseconds(CLKHALF);
  golo(_ps2clk);	
  delayMicroseconds(CLKFULL);
  gohi(_ps2clk);
  delayMicroseconds(CLKHALF);

  delayMicroseconds(50);
  return 0;
}


int PS2dev::read(unsigned char * value)
{
  unsigned char data = 0x00;
  unsigned char i;
  unsigned char bit = 0x01;
  
  unsigned char parity = 1;
  
  //wait for data line to go low
  while (digitalRead(_ps2data) == HIGH) {

  } 
  //wait for clock line to go high
  while (digitalRead(_ps2clk) == LOW) {

  } 

  
  delayMicroseconds(CLKHALF);
  golo(_ps2clk);
  delayMicroseconds(CLKFULL);
  gohi(_ps2clk);
  delayMicroseconds(CLKHALF);

  for (i=0; i < 8; i++)
    {
      if (digitalRead(_ps2data) == HIGH)
	{
	  data = data | bit;
	} else {
      }


      bit = bit << 1;
      
      delayMicroseconds(CLKHALF);
      golo(_ps2clk);	
      delayMicroseconds(CLKFULL);
      gohi(_ps2clk);
      delayMicroseconds(CLKHALF);
      
      parity = parity ^ (data & 0x01);
    }
  // we do the delay at the end of the loop, so at this point we have
  // already done the delay for the parity bit

  // stop bit
  delayMicroseconds(CLKHALF);
  golo(_ps2clk);	
  delayMicroseconds(CLKFULL);
  gohi(_ps2clk);
  delayMicroseconds(CLKHALF);
  

  delayMicroseconds(CLKHALF);
  golo(_ps2data);
  golo(_ps2clk);	
  delayMicroseconds(CLKFULL);
  gohi(_ps2clk);
  delayMicroseconds(CLKHALF);
  gohi(_ps2data);


  *value = data;
  
  return 0;
}