/************************************************************************

Radio switch servo decoder

Copyright (c) 2002 Andy Birkett

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You may view the GNU General Public License at http://www.gnu.org/copyleft/gpl.html
or write to:
the Free Software Foundation, Inc.,
59 Temple Place - Suite 330,
Boston, MA  02111-1307, USA.

mailto:AndyBirkett.Planes@gaspode.co.uk

http://www.gaspode.co.uk

************************************************************************/
/*
16f84:
;            ---------
;     <->RA2 |1    18| RA1<->
;     <->RA3 |2    17| RA0<->
;     <->RA4 |3    16| osc -xtal---||--0V
;     -->CLR |4    15| osc -xtal---||--0V
;         0V |5    14| 5V
; int <->RB0 |6    13| RB7<-> int <RB4-7>
;     <->RB1 |7    12| RB6<-> int <RB4-7>
;     <->RB2 |8    11| RB5<-> int <RB4-7>
;     <->RB3 |9    10| RB4<-> int <RB4-7>
;            ---------

12C508a:

;                  ---------
;               5V |1    18| 0V
; elevatorB <->GP5 |2    17| GP0<-> Throttle
; elevatorA <->GP4 |3    16| GP1<-> RudderA
; rx i/p    -->GP3 |4    15| GP2<-> RudderB
;                  ---------



*/

/*

What a servo o/p look like:

                <-------------- 21 ms -------------------------->               

                   <- 1 to 2.5ms ->
                -----------------                               ----
channel x     --                 -------------------------------

  typical values

                Mine,         Colins   worst case   Used ( 1 lot of 35 towards centre)
 full trim       990 (est)    1010      n/a
left / up       1120          1090      1120        1155
centre          1520          1500      1500        1500
right / down    1980          1950      1950        1915
 full trim      2110 (est)    2070      n/a

  for simple switch operation

  if < 1300 => left
  if > 1700 => right
  otherwise centre

*/


// 16F84A can be used for testing the code
 #define PIC84

// Skip settle time  for simulation
//#define SIMULATE

#ifdef PIC84

#include "..\compiler\cc5xfree\16f84a.h"
#define CP_off  |= 0x3FF8

#pragma config PWRTE=on, WDTE=off, FOSC=HS, CP_off

#else

#include "..\compiler\cc5xfree\12C508a.h"

/*
bit 0  0}
bit 1  1}=> Internal RC
bit 2  0=>Watchdog disabled
bit 3  1=>No code protecr
bit 4  0=>mclr pin NOT used
*/
#define NO_MCLR     &= ~0x80
#define CP_off      |= 0xFFE8
#define INTERNAL_RX |= 2

#pragma config  INTERNAL_RX, CP_off, WDTE=off

#endif

/***********/
/* DEFINES */
/***********/

#define LEFT   0
#define CENTRE 1
#define RIGHT  2
  

#define PRESCALER_VALUE   3     //A value of 3 gives a pre-scaler of 16, this meas the counter will count to 4096µS

#define MICRO_SECONDS_AT_FULL_COUNT 4096
#define MICRO_SECONDS_PER_COUNT     (4096/256)

#define STICK_LEFT_TIME   1300
#define STICK_RIGHT_TIME  1700

#define STICK_LEFT_COUNT  (STICK_LEFT_TIME / MICRO_SECONDS_PER_COUNT)   // 81
#define STICK_RIGHT_COUNT  (STICK_RIGHT_TIME / MICRO_SECONDS_PER_COUNT)  // 106

#define FALSE                   0
#define TRUE                    1


/************/
/* VARIABLES */
/************/

#ifdef PIC84

/* Outputs */

// Assignment for PIC84
#pragma bit OP_LEFT         @ PORTB.0
#pragma bit OP_RIGHT        @ PORTB.1
#pragma bit OP_LEFT_TOGGLE  @ PORTB.2
#pragma bit OP_RIGHT_TOGGLE @ PORTB.3
#pragma bit OP_CENTRE       @ PORTA.0

/* Input */
#pragma bit ip_rx @ PORTB.6  // bit stream from receiver


#else

/* Outputs */

// Assignment for PIC12508
#pragma bit OP_LEFT         @ GPIO.0
#pragma bit OP_RIGHT        @ GPIO.1
#pragma bit OP_LEFT_TOGGLE  @ GPIO.2
// Note a gap since we can't use bit 3 of gpio as o/p
#pragma bit OP_RIGHT_TOGGLE @ GPIO.4
#pragma bit OP_CENTRE       @ GPIO.5

/* Input */
// NB bit 3 must be an input
#pragma bit ip_rx @ GPIO.3  // bit stream from receiver

#endif


// General counter
unsigned char nTimer;

unsigned char nLastPosition;



/************************************************************/
// Routine to read the input and measure how long it is high
/************************************************************/
static void ReadInput()
{
      // Initally look a low
      while (ip_rx)
      {
      }

      // Now wait for it to go high
      while (!ip_rx)
      {
      }

      // measure how long it is high
      TMR0 = 0;
      while (ip_rx)
      {
      }

      // and return the value
      nTimer = TMR0;

} // static char ReadInput()



void waitHalfSecond()
{
unsigned long nDelay;

// each loop takes 10µS
for (nDelay=0;nDelay < (500000/10);nDelay++);
}


/***************************************************************/
/* MAIN                                                        */
/***************************************************************/


void main( void)
{
#ifdef PIC84
  // switch banks during inittialisation
  #pragma update_RP 1

  PORTA = 0;

  TRISA = 0xF0;         /* bit 0..3 outputs */

  TRISB = 0xF0;          /* bit 0..3 outputs */

#else

  OSCCAL = W;
  GPIO = 0;
  TRIS = 0x08;        /* bit 3 i/p bits 0,1,2,4,5 o/p */

#endif


#ifdef PIC84

//  OPTION = 0x0;         /* prescaler divide by 2 */
//  PSA = 1;              /* prescale WDT */

  OPTION = PRESCALER_VALUE;         /* prescale timer by 16 */
//    RBPU_ = 1;

#else

//  OPTION = 0x8;         /* prescaler divide by 2 - prescale WDT */

  OPTION = PRESCALER_VALUE;         /* prescale timer by 16 */

#endif


  TMR0 = 0;

#ifdef PIC84
  // don't switch banks again
  #pragma update_RP 0
#endif

  nTimer = 0;
  nLastPosition = CENTRE;

#ifndef SIMULATE

  // wait for everything to settle!!!
  waitHalfSecond();
  waitHalfSecond();


#endif


  // Main loop
  while (1)
  {

    // Read current value of servo input
    ReadInput();

    if (nTimer < STICK_LEFT_COUNT)
    {
      // stick is left

      OP_LEFT = TRUE;
      OP_RIGHT = FALSE;
      OP_CENTRE = FALSE;

      if (nLastPosition != LEFT)
        OP_LEFT_TOGGLE = !OP_LEFT_TOGGLE;

      nLastPosition = LEFT;
    }
    else if (nTimer > STICK_RIGHT_COUNT)
    {
      // stick is right

      OP_LEFT = FALSE;
      OP_RIGHT = TRUE;
      OP_CENTRE = FALSE;

      if (nLastPosition != RIGHT)
        OP_RIGHT_TOGGLE = !OP_RIGHT_TOGGLE;

      nLastPosition = RIGHT;
    }
    else
    {
      // stick is in the middle
      OP_LEFT = FALSE;
      OP_RIGHT = FALSE;
      OP_CENTRE = TRUE;

      nLastPosition = CENTRE;
    }

  } // while (1)

} // main