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machine: refactor PWM support
This commit refactors PWM support in the machine package to be more flexible. The new API can be used to produce tones at a specific frequency and control servos in a portable way, by abstracting over counter widths and prescalers.
This commit is contained in:
Ayke van Laethem
committed by
Ron Evans
Ron Evans
parent
f880950c3e
commit
72acda22b0
@@ -4,6 +4,7 @@ package machine
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import (
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"device/avr"
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"runtime/interrupt"
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"runtime/volatile"
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)
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@@ -21,71 +22,432 @@ func (p Pin) getPortMask() (*volatile.Register8, uint8) {
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}
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}
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// InitPWM initializes the registers needed for PWM.
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func InitPWM() {
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// use waveform generation
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avr.TCCR0A.SetBits(avr.TCCR0A_WGM00)
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// set timer 0 prescale factor to 64
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avr.TCCR0B.SetBits(avr.TCCR0B_CS01 | avr.TCCR0B_CS00)
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// set timer 1 prescale factor to 64
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avr.TCCR1B.SetBits(avr.TCCR1B_CS11)
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// put timer 1 in 8-bit phase correct pwm mode
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avr.TCCR1A.SetBits(avr.TCCR1A_WGM10)
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// set timer 2 prescale factor to 64
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avr.TCCR2B.SetBits(avr.TCCR2B_CS22)
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// configure timer 2 for phase correct pwm (8-bit)
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avr.TCCR2A.SetBits(avr.TCCR2A_WGM20)
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// PWM is one PWM peripheral, which consists of a counter and two output
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// channels (that can be connected to two fixed pins). You can set the frequency
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// using SetPeriod, but only for all the channels in this PWM peripheral at
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// once.
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type PWM struct {
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num uint8
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}
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// Configure configures a PWM pin for output.
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func (pwm PWM) Configure() error {
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switch pwm.Pin / 8 {
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case 0: // port B
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avr.DDRB.SetBits(1 << uint8(pwm.Pin))
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case 2: // port D
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avr.DDRD.SetBits(1 << uint8(pwm.Pin-16))
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var (
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Timer0 = PWM{0} // 8 bit timer for PD5 and PD6
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Timer1 = PWM{1} // 16 bit timer for PB1 and PB2
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Timer2 = PWM{2} // 8 bit timer for PB3 and PD3
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)
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// Configure enables and configures this PWM.
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//
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// For the two 8 bit timers, there is only a limited number of periods
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// available, namely the CPU frequency divided by 256 and again divided by 1, 8,
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// 64, 256, or 1024. For a MCU running at 16MHz, this would be a period of 16µs,
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// 128µs, 1024µs, 4096µs, or 16384µs.
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func (pwm PWM) Configure(config PWMConfig) error {
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switch pwm.num {
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case 0, 2: // 8-bit timers (Timer/counter 0 and Timer/counter 2)
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// Calculate the timer prescaler.
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// While we could configure a flexible top, that would sacrifice one of
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// the PWM output compare registers and thus a PWM channel. I've chosen
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// to instead limit this timer to a fixed number of frequencies.
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var prescaler uint8
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switch config.Period {
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case 0, (uint64(1e9) * 256 * 1) / uint64(CPUFrequency()):
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prescaler = 1
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case (uint64(1e9) * 256 * 8) / uint64(CPUFrequency()):
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prescaler = 2
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case (uint64(1e9) * 256 * 64) / uint64(CPUFrequency()):
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prescaler = 3
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case (uint64(1e9) * 256 * 256) / uint64(CPUFrequency()):
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prescaler = 4
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case (uint64(1e9) * 256 * 1024) / uint64(CPUFrequency()):
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prescaler = 5
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default:
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return ErrPWMPeriodTooLong
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}
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if pwm.num == 0 {
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avr.TCCR0B.Set(prescaler)
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// Set the PWM mode to fast PWM (mode = 3).
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avr.TCCR0A.Set(avr.TCCR0A_WGM00 | avr.TCCR0A_WGM01)
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} else {
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avr.TCCR2B.Set(prescaler)
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// Set the PWM mode to fast PWM (mode = 3).
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avr.TCCR2A.Set(avr.TCCR2A_WGM20 | avr.TCCR2A_WGM21)
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}
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case 1: // Timer/counter 1
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// The top value is the number of PWM ticks a PWM period takes. It is
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// initially picked assuming an unlimited counter top and no PWM
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// prescaler.
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var top uint64
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if config.Period == 0 {
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// Use a top appropriate for LEDs. Picking a relatively low period
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// here (0xff) for consistency with the other timers.
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top = 0xff
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} else {
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// The formula below calculates the following formula, optimized:
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// top = period * (CPUFrequency() / 1e9)
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// By dividing the CPU frequency first (an operation that is easily
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// optimized away) the period has less chance of overflowing.
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top = config.Period * (uint64(CPUFrequency()) / 1000000) / 1000
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}
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avr.TCCR1A.Set(avr.TCCR1A_WGM11)
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// The ideal PWM period may be larger than would fit in the PWM counter,
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// which is 16 bits (see maxTop). Therefore, try to make the PWM clock
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// speed lower with a prescaler to make the top value fit the maximum
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// top value.
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const maxTop = 0x10000
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switch {
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case top <= maxTop:
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avr.TCCR1B.Set(3<<3 | 1) // no prescaling
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case top/8 <= maxTop:
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avr.TCCR1B.Set(3<<3 | 2) // divide by 8
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top /= 8
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case top/64 <= maxTop:
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avr.TCCR1B.Set(3<<3 | 3) // divide by 64
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top /= 64
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case top/256 <= maxTop:
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avr.TCCR1B.Set(3<<3 | 4) // divide by 256
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top /= 256
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case top/1024 <= maxTop:
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avr.TCCR1B.Set(3<<3 | 5) // divide by 1024
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top /= 1024
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default:
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return ErrPWMPeriodTooLong
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}
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// A top of 0x10000 is at 100% duty cycle. Subtract one because the
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// counter counts from 0, not 1 (avoiding an off-by-one).
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top -= 1
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avr.ICR1H.Set(uint8(top >> 8))
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avr.ICR1L.Set(uint8(top))
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}
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return nil
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}
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// Set turns on the duty cycle for a PWM pin using the provided value. On the AVR this is normally a
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// 8-bit value ranging from 0 to 255.
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func (pwm PWM) Set(value uint16) {
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value8 := uint8(value >> 8)
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switch pwm.Pin {
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case PD3:
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// connect pwm to pin on timer 2, channel B
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avr.TCCR2A.SetBits(avr.TCCR2A_COM2B1)
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avr.OCR2B.Set(value8) // set pwm duty
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case PD5:
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// connect pwm to pin on timer 0, channel B
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avr.TCCR0A.SetBits(avr.TCCR0A_COM0B1)
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avr.OCR0B.Set(value8) // set pwm duty
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case PD6:
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// connect pwm to pin on timer 0, channel A
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avr.TCCR0A.SetBits(avr.TCCR0A_COM0A1)
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avr.OCR0A.Set(value8) // set pwm duty
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case PB1:
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// connect pwm to pin on timer 1, channel A
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avr.TCCR1A.SetBits(avr.TCCR1A_COM1A1)
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// this is a 16-bit value, but we only currently allow the low order bits to be set
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avr.OCR1AL.Set(value8) // set pwm duty
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case PB2:
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// connect pwm to pin on timer 1, channel B
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avr.TCCR1A.SetBits(avr.TCCR1A_COM1B1)
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// this is a 16-bit value, but we only currently allow the low order bits to be set
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avr.OCR1BL.Set(value8) // set pwm duty
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case PB3:
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// connect pwm to pin on timer 2, channel A
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avr.TCCR2A.SetBits(avr.TCCR2A_COM2A1)
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avr.OCR2A.Set(value8) // set pwm duty
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default:
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panic("Invalid PWM pin")
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// SetPeriod updates the period of this PWM peripheral.
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// To set a particular frequency, use the following formula:
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//
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// period = 1e9 / frequency
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//
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// If you use a period of 0, a period that works well for LEDs will be picked.
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//
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// SetPeriod will not change the prescaler, but also won't change the current
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// value in any of the channels. This means that you may need to update the
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// value for the particular channel.
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//
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// Note that you cannot pick any arbitrary period after the PWM peripheral has
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// been configured. If you want to switch between frequencies, pick the lowest
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// frequency (longest period) once when calling Configure and adjust the
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// frequency here as needed.
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func (pwm PWM) SetPeriod(period uint64) error {
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if pwm.num != 1 {
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return ErrPWMPeriodTooLong // TODO better error message
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}
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// The top value is the number of PWM ticks a PWM period takes. It is
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// initially picked assuming an unlimited counter top and no PWM
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// prescaler.
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var top uint64
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if period == 0 {
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// Use a top appropriate for LEDs. Picking a relatively low period
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// here (0xff) for consistency with the other timers.
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top = 0xff
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} else {
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// The formula below calculates the following formula, optimized:
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// top = period * (CPUFrequency() / 1e9)
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// By dividing the CPU frequency first (an operation that is easily
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// optimized away) the period has less chance of overflowing.
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top = period * (uint64(CPUFrequency()) / 1000000) / 1000
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}
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prescaler := avr.TCCR1B.Get() & 0x7
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switch prescaler {
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case 1:
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top /= 1
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case 2:
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top /= 8
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case 3:
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top /= 64
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case 4:
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top /= 256
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case 5:
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top /= 1024
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}
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// A top of 0x10000 is at 100% duty cycle. Subtract one because the counter
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// counts from 0, not 1 (avoiding an off-by-one).
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top -= 1
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if top > 0xffff {
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return ErrPWMPeriodTooLong
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}
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// Warning: this change is not atomic!
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avr.ICR1H.Set(uint8(top >> 8))
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avr.ICR1L.Set(uint8(top))
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// ... and because of that, set the counter back to zero to avoid most of
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// the effects of this non-atomicity.
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avr.TCNT1H.Set(0)
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avr.TCNT1L.Set(0)
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return nil
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}
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// Top returns the current counter top, for use in duty cycle calculation. It
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// will only change with a call to Configure or SetPeriod, otherwise it is
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// constant.
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//
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// The value returned here is hardware dependent. In general, it's best to treat
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// it as an opaque value that can be divided by some number and passed to Set
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// (see Set documentation for more information).
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func (pwm PWM) Top() uint32 {
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if pwm.num == 1 {
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// Timer 1 has a configurable top value.
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low := avr.ICR1L.Get()
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high := avr.ICR1H.Get()
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return uint32(high)<<8 | uint32(low) + 1
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}
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// Other timers go from 0 to 0xff (0x100 or 256 in total).
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return 256
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}
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// Counter returns the current counter value of the timer in this PWM
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// peripheral. It may be useful for debugging.
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func (pwm PWM) Counter() uint32 {
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switch pwm.num {
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case 0:
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return uint32(avr.TCNT0.Get())
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case 1:
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mask := interrupt.Disable()
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low := avr.TCNT1L.Get()
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high := avr.TCNT1H.Get()
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interrupt.Restore(mask)
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return uint32(high)<<8 | uint32(low)
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case 2:
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return uint32(avr.TCNT2.Get())
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}
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// Unknown PWM.
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return 0
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}
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// Period returns the used PWM period in nanoseconds. It might deviate slightly
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// from the configured period due to rounding.
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func (pwm PWM) Period() uint64 {
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var prescaler uint8
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switch pwm.num {
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case 0:
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prescaler = avr.TCCR0B.Get() & 0x7
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case 1:
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prescaler = avr.TCCR1B.Get() & 0x7
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case 2:
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prescaler = avr.TCCR2B.Get() & 0x7
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}
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top := uint64(pwm.Top())
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switch prescaler {
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case 1: // prescaler 1
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return 1 * top * 1000 / uint64(CPUFrequency()/1e6)
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case 2: // prescaler 8
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return 8 * top * 1000 / uint64(CPUFrequency()/1e6)
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case 3: // prescaler 64
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return 64 * top * 1000 / uint64(CPUFrequency()/1e6)
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case 4: // prescaler 256
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return 256 * top * 1000 / uint64(CPUFrequency()/1e6)
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case 5: // prescaler 1024
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return 1024 * top * 1000 / uint64(CPUFrequency()/1e6)
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default: // unknown clock source
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return 0
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}
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}
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// Channel returns a PWM channel for the given pin.
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func (pwm PWM) Channel(pin Pin) (uint8, error) {
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pin.Configure(PinConfig{Mode: PinOutput})
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pin.Low()
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switch pwm.num {
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case 0:
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switch pin {
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case PD6: // channel A
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avr.TCCR0A.SetBits(avr.TCCR0A_COM0A1)
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return 0, nil
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case PD5: // channel B
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avr.TCCR0A.SetBits(avr.TCCR0A_COM0B1)
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return 1, nil
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}
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case 1:
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switch pin {
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case PB1: // channel A
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avr.TCCR1A.SetBits(avr.TCCR1A_COM1A1)
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return 0, nil
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case PB2: // channel B
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avr.TCCR1A.SetBits(avr.TCCR1A_COM1B1)
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return 1, nil
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}
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case 2:
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switch pin {
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case PB3: // channel A
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avr.TCCR2A.SetBits(avr.TCCR2A_COM2A1)
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return 0, nil
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case PD3: // channel B
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avr.TCCR2A.SetBits(avr.TCCR2A_COM2B1)
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return 1, nil
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}
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}
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return 0, ErrInvalidOutputPin
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}
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// SetInverting sets whether to invert the output of this channel.
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// Without inverting, a 25% duty cycle would mean the output is high for 25% of
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// the time and low for the rest. Inverting flips the output as if a NOT gate
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// was placed at the output, meaning that the output would be 25% low and 75%
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// high with a duty cycle of 25%.
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//
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// Note: the invert state may not be applied on the AVR until the next call to
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// ch.Set().
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func (pwm PWM) SetInverting(channel uint8, inverting bool) {
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switch pwm.num {
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case 0:
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switch channel {
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case 0: // channel A
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if inverting {
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avr.PORTB.SetBits(1 << 6) // PB6 high
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avr.TCCR0A.SetBits(avr.TCCR0A_COM0A0)
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} else {
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avr.PORTB.ClearBits(1 << 6) // PB6 low
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avr.TCCR0A.ClearBits(avr.TCCR0A_COM0A0)
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}
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case 1: // channel B
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if inverting {
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avr.PORTB.SetBits(1 << 5) // PB5 high
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avr.TCCR0A.SetBits(avr.TCCR0A_COM0B0)
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} else {
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avr.PORTB.ClearBits(1 << 5) // PB5 low
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avr.TCCR0A.ClearBits(avr.TCCR0A_COM0B0)
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}
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}
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case 1:
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// Note: the COM1A0/COM1B0 bit is not set with the configuration below.
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// It will be set the following call to Set(), however.
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switch channel {
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case 0: // channel A, PB1
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if inverting {
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avr.PORTB.SetBits(1 << 1) // PB1 high
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} else {
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avr.PORTB.ClearBits(1 << 1) // PB1 low
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}
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case 1: // channel B, PB2
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if inverting {
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avr.PORTB.SetBits(1 << 2) // PB2 high
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} else {
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avr.PORTB.ClearBits(1 << 2) // PB2 low
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}
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}
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case 2:
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switch channel {
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case 0: // channel A
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if inverting {
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avr.PORTB.SetBits(1 << 3) // PB3 high
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avr.TCCR2A.SetBits(avr.TCCR2A_COM2A0)
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} else {
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avr.PORTB.ClearBits(1 << 3) // PB3 low
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avr.TCCR2A.ClearBits(avr.TCCR2A_COM2A0)
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}
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case 1: // channel B
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if inverting {
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avr.PORTD.SetBits(1 << 3) // PD3 high
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avr.TCCR2A.SetBits(avr.TCCR2A_COM2B0)
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} else {
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avr.PORTD.ClearBits(1 << 3) // PD3 low
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avr.TCCR2A.ClearBits(avr.TCCR2A_COM2B0)
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}
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}
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}
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}
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// Set updates the channel value. This is used to control the channel duty
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// cycle, in other words the fraction of time the channel output is high (or low
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// when inverted). For example, to set it to a 25% duty cycle, use:
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//
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// pwm.Set(channel, pwm.Top() / 4)
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//
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// pwm.Set(channel, 0) will set the output to low and pwm.Set(channel,
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// pwm.Top()) will set the output to high, assuming the output isn't inverted.
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func (pwm PWM) Set(channel uint8, value uint32) {
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switch pwm.num {
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case 0:
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value := uint16(value)
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switch channel {
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case 0: // channel A
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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
|
||||
if value == 0 {
|
||||
avr.TCCR0A.ClearBits(avr.TCCR0A_COM0B1)
|
||||
} else {
|
||||
avr.OCR0B.Set(uint8(value) - 1)
|
||||
avr.TCCR0A.SetBits(avr.TCCR0A_COM0B1)
|
||||
}
|
||||
}
|
||||
case 1:
|
||||
mask := interrupt.Disable()
|
||||
switch channel {
|
||||
case 0: // channel A, PB1
|
||||
if value == 0 {
|
||||
avr.TCCR1A.ClearBits(avr.TCCR1A_COM1A1 | avr.TCCR1A_COM1A0)
|
||||
} else {
|
||||
value := uint16(value) - 1 // yes, this is safe (it relies on underflow)
|
||||
avr.OCR1AH.Set(uint8(value >> 8))
|
||||
avr.OCR1AL.Set(uint8(value))
|
||||
if avr.PORTB.HasBits(1 << 1) { // is PB1 high?
|
||||
// Yes, set the inverting bit.
|
||||
avr.TCCR1A.SetBits(avr.TCCR1A_COM1A1 | avr.TCCR1A_COM1A0)
|
||||
} else {
|
||||
// No, output is non-inverting.
|
||||
avr.TCCR1A.SetBits(avr.TCCR1A_COM1A1)
|
||||
}
|
||||
}
|
||||
case 1: // channel B, PB2
|
||||
if value == 0 {
|
||||
avr.TCCR1A.ClearBits(avr.TCCR1A_COM1B1 | avr.TCCR1A_COM1B0)
|
||||
} else {
|
||||
value := uint16(value) - 1 // yes, this is safe (it relies on underflow)
|
||||
avr.OCR1BH.Set(uint8(value >> 8))
|
||||
avr.OCR1BL.Set(uint8(value))
|
||||
if avr.PORTB.HasBits(1 << 2) { // is PB2 high?
|
||||
// Yes, set the inverting bit.
|
||||
avr.TCCR1A.SetBits(avr.TCCR1A_COM1B1 | avr.TCCR1A_COM1B0)
|
||||
} else {
|
||||
// No, output is non-inverting.
|
||||
avr.TCCR1A.SetBits(avr.TCCR1A_COM1B1)
|
||||
}
|
||||
}
|
||||
}
|
||||
interrupt.Restore(mask)
|
||||
case 2:
|
||||
value := uint16(value)
|
||||
switch channel {
|
||||
case 0: // channel A
|
||||
if value == 0 {
|
||||
avr.TCCR2A.ClearBits(avr.TCCR2A_COM2A1)
|
||||
} else {
|
||||
avr.OCR2A.Set(uint8(value - 1))
|
||||
avr.TCCR2A.SetBits(avr.TCCR2A_COM2A1)
|
||||
}
|
||||
case 1: // channel B
|
||||
if value == 0 {
|
||||
avr.TCCR2A.ClearBits(avr.TCCR2A_COM2B1)
|
||||
} else {
|
||||
avr.OCR2B.Set(uint8(value - 1))
|
||||
avr.TCCR2A.SetBits(avr.TCCR2A_COM2B1)
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
|
||||
Reference in New Issue
Block a user