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755 | killagreg | 1 | #include <avr/io.h> |
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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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762 | killagreg | 13 | // Port PC5 connected to PWM output from compass module |
755 | killagreg | 14 | DDRC &= ~(1<<DDC4); // set as input |
762 | killagreg | 15 | PORTC |= (1<<PORTC4); // pull up to increase PWM counter allo if nothing is connected |
755 | killagreg | 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 | } |