1 | // Testing interrupt-based analog reading
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2 | // ATMega328p
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3 |
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4 | // Note, many macro values are defined in <avr/io.h> and
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5 | // <avr/interrupts.h>, which are included automatically by
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6 | // the Arduino interface
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7 |
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8 | // High when a value is ready to be read
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9 | volatile int readFlag;
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10 |
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11 | // Value to store analog result
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12 | volatile int analogVal;
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13 |
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14 |
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15 | // Initialization
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16 | void setup(){
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17 |
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18 | // clear ADLAR in ADMUX (0x7C) to right-adjust the result
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19 | // ADCL will contain lower 8 bits, ADCH upper 2 (in last two bits)
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20 | ADMUX &= B11011111;
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21 |
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22 | // Set REFS1..0 in ADMUX (0x7C) to change reference voltage to the
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23 | // proper source (01)
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24 | ADMUX |= B01000000;
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25 |
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26 | // Clear MUX3..0 in ADMUX (0x7C) in preparation for setting the analog
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27 | // input
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28 | ADMUX &= B11110000;
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29 |
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30 | // Set MUX3..0 in ADMUX (0x7C) to read from AD8 (Internal temp)
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31 | // Do not set above 15! You will overrun other parts of ADMUX. A full
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32 | // list of possible inputs is available in Table 24-4 of the ATMega328
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33 | // datasheet
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34 | ADMUX |= 8;
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35 | // ADMUX |= B00001000; // Binary equivalent
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36 |
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37 | // Set ADEN in ADCSRA (0x7A) to enable the ADC.
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38 | // Note, this instruction takes 12 ADC clocks to execute
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39 | ADCSRA |= B10000000;
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40 |
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41 | // Set ADATE in ADCSRA (0x7A) to enable auto-triggering.
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42 | ADCSRA |= B00100000;
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43 |
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44 | // Clear ADTS2..0 in ADCSRB (0x7B) to set trigger mode to free running.
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45 | // This means that as soon as an ADC has finished, the next will be
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46 | // immediately started.
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47 | ADCSRB &= B11111000;
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48 |
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49 | // Set the Prescaler to 128 (16000KHz/128 = 125KHz)
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50 | // Above 200KHz 10-bit results are not reliable.
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51 | ADCSRA |= B00000111;
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52 |
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53 | // Set ADIE in ADCSRA (0x7A) to enable the ADC interrupt.
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54 | // Without this, the internal interrupt will not trigger.
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55 | ADCSRA |= B00001000;
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56 |
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57 | // Enable global interrupts
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58 | // AVR macro included in <avr/interrupts.h>, which the Arduino IDE
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59 | // supplies by default.
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60 | sei();
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61 |
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62 | // Kick off the first ADC
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63 | readFlag = 0;
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64 | // Set ADSC in ADCSRA (0x7A) to start the ADC conversion
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65 | ADCSRA |=B01000000;
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66 | }
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67 |
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68 |
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69 | // Processor loop
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70 | void loop(){
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71 |
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72 | // Check to see if the value has been updated
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73 | if (readFlag == 1){
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74 |
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75 | // Perform whatever updating needed
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76 |
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77 | readFlag = 0;
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78 | }
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79 |
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80 | // Whatever else you would normally have running in loop().
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81 |
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82 | }
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83 |
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84 |
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85 | // Interrupt service routine for the ADC completion
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86 | ISR(ADC_vect){
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87 |
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88 | // Done reading
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89 | readFlag = 1;
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90 |
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91 | // Must read low first
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92 | analogVal = ADCL | (ADCH << 8);
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93 |
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94 | // Not needed because free-running mode is enabled.
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95 | // Set ADSC in ADCSRA (0x7A) to start another ADC conversion
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96 | // ADCSRA |= B01000000;
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97 | }
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