Rev 762 | Go to most recent revision | Details | Last modification | View Log | RSS feed
| Rev | Author | Line No. | Line |
|---|---|---|---|
| 755 | killagreg | 1 | #include <avr/io.h> |
| 2 | |||
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| 5 | int32_t PWMHeading = -1; |
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| 6 | uint8_t PWMTimeout = 0; |
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| 7 | |||
| 8 | /*********************************************/ |
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| 9 | /* Initialize Interface to CMPS02 Compass */ |
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| 10 | /*********************************************/ |
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| 11 | void CMPS03_Init(void) |
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| 12 | { |
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| 13 | // Port PC4 connected to PWM output from compass module |
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| 14 | DDRC &= ~(1<<DDC4); // set as input |
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| 15 | PORTC |= (1<<PORTC4); // pull up to increase PWM counter aslo if nowthing is connected |
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| 16 | |||
| 17 | PWMTimeout = 0; |
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| 18 | } |
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| 19 | |||
| 20 | |||
| 21 | /*********************************************/ |
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| 22 | /* Get Data from CMPS03 */ |
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| 23 | /*********************************************/ |
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| 24 | void CMPS03_Update(void) // called every 102.4 us by timer 0 ISR |
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| 25 | { |
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| 26 | static uint16_t PWMCount = 0; |
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| 27 | // The pulse width varies from 1ms (0°) to 36.99ms (359.9°) |
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| 28 | // in other words 100us/° with a +1ms offset. |
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| 29 | // The signal goes low for 65ms between pulses, |
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| 30 | // so the cycle time is 65mS + the pulse width. |
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| 31 | // The pulse is generated by a 16 bit timer in the processor |
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| 32 | // giving a 1uS resolution, however I would not recommend |
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| 33 | // measuring this to anything better than 0.1° (10uS). |
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| 34 | |||
| 35 | if(PINC & (1<<PINC4)) |
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| 36 | { // If PWM signal is high increment PWM high counter |
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| 37 | // This counter is incremented by a periode of 102.4us, |
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| 38 | // i.e. the resoluton of pwm coded heading is approx. 1 deg. |
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| 39 | PWMCount++; |
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| 40 | } |
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| 41 | else // PWM is low |
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| 42 | { |
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| 43 | if((PWMCount) && (PWMCount < 400)) |
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| 44 | { |
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| 45 | PWMHeading = (((uint32_t)PWMCount * 1024L) / 1000L) - 10; // correct timebase and offset |
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| 46 | PWMTimeout = 12; // if 12 periodes long no valid PWM was detected the data are invalid |
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| 47 | // 12 * 400 counts * 102.4 us = 419 ms |
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| 48 | } |
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| 49 | else // PWM counter is over the pwm periode of 37 ms |
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| 50 | { // overflow at low edge detection |
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| 51 | if(PWMTimeout ) PWMTimeout--; |
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| 52 | } |
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| 53 | PWMCount = 0; // reset pwm counter |
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| 54 | } |
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| 55 | // overflow without a low edge (nothing connected to PC4) |
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| 56 | if (PWMCount > 400) |
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| 57 | { |
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| 58 | if(PWMTimeout ) PWMTimeout--; |
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| 59 | PWMCount = 0; |
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| 60 | } |
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| 61 | |||
| 62 | |||
| 63 | } |
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| 64 | |||
| 65 | |||
| 66 | /*********************************************/ |
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| 67 | /* Calculate north direction (heading) */ |
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| 68 | /*********************************************/ |
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| 69 | int16_t CMPS03_Heading(void) |
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| 70 | { |
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| 71 | int16_t heading; |
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| 72 | if(PWMTimeout) |
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| 73 | { // range from 0 to 359 |
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| 74 | heading = (int16_t)PWMHeading; |
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| 75 | if (heading < 0) heading += 360; |
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| 76 | heading = heading%360; |
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| 77 | } |
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| 78 | else // no data from compass |
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| 79 | { |
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| 80 | heading = -1; |
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| 81 | } |
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| 82 | return heading; |
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| 83 | } |