diff --git a/GNUmakefile b/GNUmakefile index 99a654ca7..322c0b7cf 100644 --- a/GNUmakefile +++ b/GNUmakefile @@ -896,6 +896,8 @@ endif @$(MD5SUM) test.hex $(TINYGO) build -size short -o test.hex -target=digispark examples/blinky1 @$(MD5SUM) test.hex + $(TINYGO) build -size short -o test.hex -target=digispark examples/pwm + @$(MD5SUM) test.hex $(TINYGO) build -size short -o test.hex -target=digispark -gc=leaking examples/blinky1 @$(MD5SUM) test.hex ifneq ($(XTENSA), 0) diff --git a/src/examples/pwm/digispark.go b/src/examples/pwm/digispark.go new file mode 100644 index 000000000..848d51854 --- /dev/null +++ b/src/examples/pwm/digispark.go @@ -0,0 +1,12 @@ +//go:build digispark + +package main + +import "machine" + +var ( + // Use Timer1 for PWM (recommended for ATtiny85) + pwm = machine.Timer1 + pinA = machine.P1 // PB1, Timer1 channel A (LED pin) + pinB = machine.P4 // PB4, Timer1 channel B +) diff --git a/src/machine/board_digispark.go b/src/machine/board_digispark.go index f380aae85..d7106a554 100644 --- a/src/machine/board_digispark.go +++ b/src/machine/board_digispark.go @@ -2,17 +2,26 @@ package machine +// Digispark is a tiny ATtiny85-based board with 6 I/O pins. +// +// PWM is available on the following pins: +// - P0 (PB0): Timer0 channel A +// - P1 (PB1): Timer0 channel B or Timer1 channel A (LED pin) +// - P4 (PB4): Timer1 channel B +// +// Timer1 is recommended for PWM as it provides more flexible frequency control. + // Return the current CPU frequency in hertz. func CPUFrequency() uint32 { return 16000000 } const ( - P0 Pin = PB0 - P1 Pin = PB1 + P0 Pin = PB0 // PWM available (Timer0 OC0A) + P1 Pin = PB1 // PWM available (Timer0 OC0B or Timer1 OC1A) P2 Pin = PB2 P3 Pin = PB3 - P4 Pin = PB4 + P4 Pin = PB4 // PWM available (Timer1 OC1B) P5 Pin = PB5 LED = P1 diff --git a/src/machine/machine_attiny85.go b/src/machine/machine_attiny85.go index 33424c605..27adaf948 100644 --- a/src/machine/machine_attiny85.go +++ b/src/machine/machine_attiny85.go @@ -21,3 +21,357 @@ func (p Pin) getPortMask() (*volatile.Register8, uint8) { // Very simple for the attiny85, which only has a single port. return avr.PORTB, 1 << uint8(p) } + +// PWM is one PWM peripheral, which consists of a counter and two output +// channels (that can be connected to two fixed pins). You can set the frequency +// using SetPeriod, but only for all the channels in this PWM peripheral at +// once. +type PWM struct { + num uint8 +} + +var ( + Timer0 = PWM{0} // 8 bit timer for PB0 and PB1 + Timer1 = PWM{1} // 8 bit high-speed timer for PB1 and PB4 +) + +// GTCCR bits for Timer1 that are not defined in the device file +const ( + gtccrPWM1B = 0x40 // Pulse Width Modulator B Enable + gtccrCOM1B0 = 0x10 // Comparator B Output Mode bit 0 + gtccrCOM1B1 = 0x20 // Comparator B Output Mode bit 1 +) + +// Configure enables and configures this PWM. +// +// For Timer0, there is only a limited number of periods available, namely the +// CPU frequency divided by 256 and again divided by 1, 8, 64, 256, or 1024. +// For a MCU running at 8MHz, this would be a period of 32µs, 256µs, 2048µs, +// 8192µs, or 32768µs. +// +// For Timer1, the period is more flexible as it uses OCR1C as the top value. +// Timer1 also supports more prescaler values (1 to 16384). +func (pwm PWM) Configure(config PWMConfig) error { + switch pwm.num { + case 0: // Timer/Counter 0 (8-bit) + // Calculate the timer prescaler. + var prescaler uint8 + switch config.Period { + case 0, (uint64(1e9) * 256 * 1) / uint64(CPUFrequency()): + prescaler = 1 + case (uint64(1e9) * 256 * 8) / uint64(CPUFrequency()): + prescaler = 2 + case (uint64(1e9) * 256 * 64) / uint64(CPUFrequency()): + prescaler = 3 + case (uint64(1e9) * 256 * 256) / uint64(CPUFrequency()): + prescaler = 4 + case (uint64(1e9) * 256 * 1024) / uint64(CPUFrequency()): + prescaler = 5 + default: + return ErrPWMPeriodTooLong + } + + avr.TCCR0B.Set(prescaler) + // Set the PWM mode to fast PWM (mode = 3). + avr.TCCR0A.Set(avr.TCCR0A_WGM00 | avr.TCCR0A_WGM01) + + case 1: // Timer/Counter 1 (8-bit high-speed) + // Timer1 on ATtiny85 is different from ATmega328: + // - It's 8-bit with configurable top (OCR1C) + // - Has more prescaler options (1-16384) + // - PWM mode is enabled per-channel via PWM1A/PWM1B bits + var top uint64 + if config.Period == 0 { + // Use a top appropriate for LEDs. + top = 0xff + } else { + // Calculate top value: top = period * (CPUFrequency / 1e9) + top = config.Period * (uint64(CPUFrequency()) / 1000000) / 1000 + } + + // Timer1 prescaler values: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384 + const maxTop = 256 + var prescaler uint8 + switch { + case top <= maxTop: + prescaler = 1 // prescaler 1 + case top/2 <= maxTop: + prescaler = 2 // prescaler 2 + top /= 2 + case top/4 <= maxTop: + prescaler = 3 // prescaler 4 + top /= 4 + case top/8 <= maxTop: + prescaler = 4 // prescaler 8 + top /= 8 + case top/16 <= maxTop: + prescaler = 5 // prescaler 16 + top /= 16 + case top/32 <= maxTop: + prescaler = 6 // prescaler 32 + top /= 32 + case top/64 <= maxTop: + prescaler = 7 // prescaler 64 + top /= 64 + case top/128 <= maxTop: + prescaler = 8 // prescaler 128 + top /= 128 + case top/256 <= maxTop: + prescaler = 9 // prescaler 256 + top /= 256 + case top/512 <= maxTop: + prescaler = 10 // prescaler 512 + top /= 512 + case top/1024 <= maxTop: + prescaler = 11 // prescaler 1024 + top /= 1024 + case top/2048 <= maxTop: + prescaler = 12 // prescaler 2048 + top /= 2048 + case top/4096 <= maxTop: + prescaler = 13 // prescaler 4096 + top /= 4096 + case top/8192 <= maxTop: + prescaler = 14 // prescaler 8192 + top /= 8192 + case top/16384 <= maxTop: + prescaler = 15 // prescaler 16384 + top /= 16384 + default: + return ErrPWMPeriodTooLong + } + + // Set prescaler (CS1[3:0] bits) + avr.TCCR1.Set(prescaler) + // Set top value + avr.OCR1C.Set(uint8(top - 1)) + } + return nil +} + +// SetPeriod updates the period of this PWM peripheral. +// To set a particular frequency, use the following formula: +// +// period = 1e9 / frequency +// +// If you use a period of 0, a period that works well for LEDs will be picked. +// +// SetPeriod will not change the prescaler, but also won't change the current +// value in any of the channels. This means that you may need to update the +// value for the particular channel. +// +// Note that you cannot pick any arbitrary period after the PWM peripheral has +// been configured. If you want to switch between frequencies, pick the lowest +// frequency (longest period) once when calling Configure and adjust the +// frequency here as needed. +func (pwm PWM) SetPeriod(period uint64) error { + if pwm.num == 0 { + return ErrPWMPeriodTooLong // Timer0 doesn't support dynamic period + } + + // Timer1 can adjust period via OCR1C + var top uint64 + if period == 0 { + top = 0xff + } else { + top = period * (uint64(CPUFrequency()) / 1000000) / 1000 + } + + // Get current prescaler + prescaler := avr.TCCR1.Get() & 0x0f + // Timer1 prescaler values follow a power-of-2 pattern: + // prescaler n maps to divisor 2^(n-1), so we can use a simple shift + if prescaler > 0 && prescaler <= 15 { + top >>= (prescaler - 1) + } + + if top > 256 { + return ErrPWMPeriodTooLong + } + + avr.OCR1C.Set(uint8(top - 1)) + avr.TCNT1.Set(0) + + return nil +} + +// Top returns the current counter top, for use in duty cycle calculation. It +// will only change with a call to Configure or SetPeriod, otherwise it is +// constant. +// +// The value returned here is hardware dependent. In general, it's best to treat +// it as an opaque value that can be divided by some number and passed to Set +// (see Set documentation for more information). +func (pwm PWM) Top() uint32 { + if pwm.num == 1 { + // Timer1 has configurable top via OCR1C + return uint32(avr.OCR1C.Get()) + 1 + } + // Timer0 goes from 0 to 0xff (256 in total) + return 256 +} + +// Counter returns the current counter value of the timer in this PWM +// peripheral. It may be useful for debugging. +func (pwm PWM) Counter() uint32 { + switch pwm.num { + case 0: + return uint32(avr.TCNT0.Get()) + case 1: + return uint32(avr.TCNT1.Get()) + } + return 0 +} + +// Prescaler lookup tables using uint16 (more efficient than uint64 on AVR) +// Timer0 prescaler lookup table (index 0-7 maps to prescaler bits) +var timer0Prescalers = [8]uint16{0, 1, 8, 64, 256, 1024, 0, 0} + +// Timer1 prescaler lookup table (index 0-15 maps to prescaler bits) +var timer1Prescalers = [16]uint16{0, 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384} + +// Period returns the used PWM period in nanoseconds. It might deviate slightly +// from the configured period due to rounding. +func (pwm PWM) Period() uint64 { + var prescaler uint64 + switch pwm.num { + case 0: + prescalerBits := avr.TCCR0B.Get() & 0x7 + prescaler = uint64(timer0Prescalers[prescalerBits]) + if prescaler == 0 { + return 0 + } + case 1: + prescalerBits := avr.TCCR1.Get() & 0x0f + prescaler = uint64(timer1Prescalers[prescalerBits]) + if prescaler == 0 { + return 0 + } + } + top := uint64(pwm.Top()) + return prescaler * top * 1000 / uint64(CPUFrequency()/1e6) +} + +// Channel returns a PWM channel for the given pin. +func (pwm PWM) Channel(pin Pin) (uint8, error) { + pin.Configure(PinConfig{Mode: PinOutput}) + pin.Low() + switch pwm.num { + case 0: + switch pin { + case PB0: // OC0A + avr.TCCR0A.SetBits(avr.TCCR0A_COM0A1) + return 0, nil + case PB1: // OC0B + avr.TCCR0A.SetBits(avr.TCCR0A_COM0B1) + return 1, nil + } + case 1: + switch pin { + case PB1: // OC1A + // Enable PWM on channel A + avr.TCCR1.SetBits(avr.TCCR1_PWM1A | avr.TCCR1_COM1A1) + return 0, nil + case PB4: // OC1B + // Enable PWM on channel B (controlled via GTCCR) + avr.GTCCR.SetBits(gtccrPWM1B | gtccrCOM1B1) + return 1, nil + } + } + return 0, ErrInvalidOutputPin +} + +// SetInverting sets whether to invert the output of this channel. +// Without inverting, a 25% duty cycle would mean the output is high for 25% of +// the time and low for the rest. Inverting flips the output as if a NOT gate +// was placed at the output, meaning that the output would be 25% low and 75% +// high with a duty cycle of 25%. +func (pwm PWM) SetInverting(channel uint8, inverting bool) { + switch pwm.num { + case 0: + switch channel { + case 0: // channel A, PB0 + if inverting { + avr.PORTB.SetBits(1 << 0) + avr.TCCR0A.SetBits(avr.TCCR0A_COM0A0) + } else { + avr.PORTB.ClearBits(1 << 0) + avr.TCCR0A.ClearBits(avr.TCCR0A_COM0A0) + } + case 1: // channel B, PB1 + if inverting { + avr.PORTB.SetBits(1 << 1) + avr.TCCR0A.SetBits(avr.TCCR0A_COM0B0) + } else { + avr.PORTB.ClearBits(1 << 1) + avr.TCCR0A.ClearBits(avr.TCCR0A_COM0B0) + } + } + case 1: + switch channel { + case 0: // channel A, PB1 + if inverting { + avr.PORTB.SetBits(1 << 1) + avr.TCCR1.SetBits(avr.TCCR1_COM1A0) + } else { + avr.PORTB.ClearBits(1 << 1) + avr.TCCR1.ClearBits(avr.TCCR1_COM1A0) + } + case 1: // channel B, PB4 + if inverting { + avr.PORTB.SetBits(1 << 4) + avr.GTCCR.SetBits(gtccrCOM1B0) + } else { + avr.PORTB.ClearBits(1 << 4) + avr.GTCCR.ClearBits(gtccrCOM1B0) + } + } + } +} + +// Set updates the channel value. This is used to control the channel duty +// cycle, in other words the fraction of time the channel output is high (or low +// when inverted). For example, to set it to a 25% duty cycle, use: +// +// pwm.Set(channel, pwm.Top() / 4) +// +// pwm.Set(channel, 0) will set the output to low and pwm.Set(channel, +// pwm.Top()) will set the output to high, assuming the output isn't inverted. +func (pwm PWM) Set(channel uint8, value uint32) { + switch pwm.num { + case 0: + switch channel { + case 0: // channel A, PB0 + if value == 0 { + avr.TCCR0A.ClearBits(avr.TCCR0A_COM0A1) + } else { + avr.OCR0A.Set(uint8(value - 1)) + avr.TCCR0A.SetBits(avr.TCCR0A_COM0A1) + } + case 1: // channel B, PB1 + if value == 0 { + avr.TCCR0A.ClearBits(avr.TCCR0A_COM0B1) + } else { + avr.OCR0B.Set(uint8(value - 1)) + avr.TCCR0A.SetBits(avr.TCCR0A_COM0B1) + } + } + case 1: + switch channel { + case 0: // channel A, PB1 + if value == 0 { + avr.TCCR1.ClearBits(avr.TCCR1_COM1A1) + } else { + avr.OCR1A.Set(uint8(value - 1)) + avr.TCCR1.SetBits(avr.TCCR1_COM1A1) + } + case 1: // channel B, PB4 + if value == 0 { + avr.GTCCR.ClearBits(gtccrCOM1B1) + } else { + avr.OCR1B.Set(uint8(value - 1)) + avr.GTCCR.SetBits(gtccrCOM1B1) + } + } + } +}