0,0 → 1,83 |
#include <avr/io.h> |
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int32_t PWMHeading = -1; |
uint8_t PWMTimeout = 0; |
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/*********************************************/ |
/* Initialize Interface to CMPS02 Compass */ |
/*********************************************/ |
void CMPS03_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 aslo if nowthing is connected |
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PWMTimeout = 0; |
} |
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/*********************************************/ |
/* Get Data from CMPS03 */ |
/*********************************************/ |
void CMPS03_Update(void) // called every 102.4 us by timer 0 ISR |
{ |
static uint16_t PWMCount = 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. |
// The pulse is generated by a 16 bit timer in the processor |
// giving a 1uS resolution, however I would not recommend |
// measuring this to anything better than 0.1° (10uS). |
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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++; |
} |
else // PWM is low |
{ |
if((PWMCount) && (PWMCount < 400)) |
{ |
PWMHeading = (((uint32_t)PWMCount * 1024L) / 1000L) - 10; // correct timebase and offset |
PWMTimeout = 12; // if 12 periodes long no valid PWM was detected the data are invalid |
// 12 * 400 counts * 102.4 us = 419 ms |
} |
else // PWM counter is over the pwm periode of 37 ms |
{ // overflow at low edge detection |
if(PWMTimeout ) PWMTimeout--; |
} |
PWMCount = 0; // reset pwm counter |
} |
// overflow without a low edge (nothing connected to PC4) |
if (PWMCount > 400) |
{ |
if(PWMTimeout ) PWMTimeout--; |
PWMCount = 0; |
} |
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} |
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/*********************************************/ |
/* Calculate north direction (heading) */ |
/*********************************************/ |
int16_t CMPS03_Heading(void) |
{ |
int16_t heading; |
if(PWMTimeout) |
{ // range from 0 to 359 |
heading = (int16_t)PWMHeading; |
if (heading < 0) heading += 360; |
heading = heading%360; |
} |
else // no data from compass |
{ |
heading = -1; |
} |
return heading; |
} |