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#include <avr/io.h>
#include <stdlib.h>
#include <inttypes.h>
#include "timer0.h"
#include "fc.h"
#include "rc.h"
#include "eeprom.h"
#include "mk3mag.h"
uint8_t PWMTimeout = 12;
ToMk3Mag_t ToMk3Mag;
/*********************************************/
/* Initialize Interface to MK3MAG Compass */
/*********************************************/
void MK3MAG_Init(void)
{
// Port PC4 connected to PWM output from compass module
DDRC &= ~(1<<DDC4); // set as input
PORTC |= (1<<PORTC4); // pull up to increase PWM counter also if nothing is connected
PWMTimeout = 0;
ToMk3Mag.CalState = 0;
ToMk3Mag.Orientation = 1;
}
/*********************************************/
/* Get PWM from MK3MAG */
/*********************************************/
void MK3MAG_Update(void) // called every 102.4 us by timer 0 ISR
{
static uint16_t PWMCount = 0;
static uint16_t BeepDelay = 0;
// The pulse width varies from 1ms (0°) to 36.99ms (359.9°)
// in other words 100us/° with a +1ms offset.
// The signal goes low for 65ms between pulses,
// so the cycle time is 65mS + the pulse width.
// pwm is high
if(PINC & (1<<PINC4))
{ // If PWM signal is high increment PWM high counter
// This counter is incremented by a periode of 102.4us,
// i.e. the resoluton of pwm coded heading is approx. 1 deg.
PWMCount++;
// pwm overflow?
if (PWMCount > 400)
{
if(PWMTimeout) PWMTimeout--; // decrement timeout
CompassHeading = -1; // unknown heading
PWMCount = 0; // reset PWM Counter
}
}
else // pwm is low
{ // ignore pwm values values of 0 and higher than 37 ms;
if((PWMCount) && (PWMCount < 362)) // 362 * 102.4us = 37.0688 ms
{
if(PWMCount <10) CompassHeading = 0;
else CompassHeading = ((uint32_t)(PWMCount - 10) * 1049L)/1024; // correct timebase and offset
CompassOffCourse = ((540 + CompassHeading - CompassCourse) % 360) - 180;
PWMTimeout = 12; // if 12 periodes long no valid PWM was detected the data are invalid
// 12 * 362 counts * 102.4 us
}
PWMCount = 0; // reset pwm counter
}
if(!PWMTimeout)
{
if(CheckDelay(BeepDelay))
{
if(!BeepTime) BeepTime = 100; // make noise with 10Hz to signal the compass problem
BeepDelay = SetDelay(100);
}
}
}