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Adds support to user-supplied PWM frequency

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This commit is contained in:
rbaron 2021-02-10 22:49:21 +01:00
parent 11cf6583a3
commit 3652d89e77
3 changed files with 16 additions and 14 deletions
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21
code/parasite/lib/parasite/pwm.cpp
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@ -14,20 +14,21 @@ namespace {
// No scaling. The PWM counter will increase with a frequency of 16MHz. // No scaling. The PWM counter will increase with a frequency of 16MHz.
constexpr unsigned long kPWMFrequencyPrescale = PWM_PRESCALER_PRESCALER_DIV_1; constexpr unsigned long kPWMFrequencyPrescale = PWM_PRESCALER_PRESCALER_DIV_1;
// In conjunction with the PWM clock frequency, kPWMMaxCounter defines the
// frequency of the square wave.
constexpr int kPWMMaxCounter = 32;
// Since we want a duty cycle of 0.5, we flip the PVM output when the counter
// reaches kPWMMaxCounter / 2/;
constexpr int kPWMFlipCount = kPWMMaxCounter;
} // namespace } // namespace
void SetupSquareWave(int pin_number) { void SetupSquareWave(double frequency, int pin_number) {
// In conjunction with the PWM clock frequency, kPWMMaxCounter defines the
// frequency of the square wave.
const int max_count = 16e6 / frequency;
// Since we want a duty cycle of 0.5, we flip the PVM output when the counter
// reaches kPWMMaxCounter / 2/;
const int flip_at_count = max_count / 2;
HwPWM0.addPin(pin_number); HwPWM0.addPin(pin_number);
HwPWM0.setClockDiv(PWM_PRESCALER_PRESCALER_DIV_1); HwPWM0.setClockDiv(PWM_PRESCALER_PRESCALER_DIV_1);
HwPWM0.setMaxValue(kPWMMaxCounter); HwPWM0.setMaxValue(max_count);
HwPWM0.writePin(pin_number, kPWMFlipCount); HwPWM0.writePin(pin_number, flip_at_count);
HwPWM0.begin(); HwPWM0.begin();
} }

6
code/parasite/lib/parasite/pwm.h
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@ -6,9 +6,9 @@ namespace parasite {
// This is a simple, single-channel PWM-based square wave generator. // This is a simple, single-channel PWM-based square wave generator.
// This only ever works for a single pin. If you call this function // This only ever works for a single pin. If you call this function
// twice with different pin numbers, nothing good will come out of it. // twice with different pin numbers, nothing good will come out of it.
// I am particularly proud of how well I resisted making this "generic" // I am particularly proud of how well I resisted making this generic
// and "reusable". // and reusable.
void SetupSquareWave(int pin_number); void SetupSquareWave(double frequency, int pin_number);
} // namespace parasite } // namespace parasite
#endif // _PARASITE_PWM_H_ #endif // _PARASITE_PWM_H_

3
code/parasite/src/main.cpp
View file

@ -5,12 +5,13 @@
constexpr int kLED1Pin = 17; constexpr int kLED1Pin = 17;
constexpr int kLED2Pin = 18; constexpr int kLED2Pin = 18;
constexpr int kPWMPin = 19; constexpr int kPWMPin = 19;
constexpr double kPWMFrequency = 500000;
void setup() { void setup() {
Serial.begin(9600); Serial.begin(9600);
pinMode(kLED1Pin, OUTPUT); pinMode(kLED1Pin, OUTPUT);
pinMode(kLED2Pin, OUTPUT); pinMode(kLED2Pin, OUTPUT);
parasite::SetupSquareWave(kPWMPin); parasite::SetupSquareWave(kPWMFrequency, kPWMPin);
} }
void loop() { void loop() {