//go:build nrf52 || nrf52840 || nrf52833

package machine

import (
	"device/nrf"
	"runtime/volatile"
	"unsafe"
)

func CPUFrequency() uint32 {
	return 64000000
}

var adcVDDHPin = Pin(254) // special pin number for VDDH on the nrf52840

// InitADC initializes the registers needed for ADC.
func InitADC() {
	// Enable ADC.
	// The ADC does not consume a noticeable amount of current by being enabled.
	nrf.SAADC.ENABLE.Set(nrf.SAADC_ENABLE_ENABLE_Enabled << nrf.SAADC_ENABLE_ENABLE_Pos)
}

// Configure configures an ADC pin to be able to read analog data.
// Reference voltage can be 150, 300, 600, 1200, 1800, 2400, 3000(default), 3600 mV
// Resolution can be 8, 10, 12(default), 14 bits
// SampleTime will be ceiled to 3(default), 5, 10, 15, 20 or 40(max) µS respectively
// Samples can be 1(default), 2, 4, 8, 16, 32, 64, 128, 256 samples
func (a *ADC) Configure(config ADCConfig) {
	var configVal uint32 = nrf.SAADC_CH_CONFIG_RESP_Bypass<<nrf.SAADC_CH_CONFIG_RESP_Pos |
		nrf.SAADC_CH_CONFIG_RESN_Bypass<<nrf.SAADC_CH_CONFIG_RESN_Pos |
		nrf.SAADC_CH_CONFIG_REFSEL_Internal<<nrf.SAADC_CH_CONFIG_REFSEL_Pos |
		nrf.SAADC_CH_CONFIG_MODE_SE<<nrf.SAADC_CH_CONFIG_MODE_Pos

	switch config.Reference {
	case 150: // 0.15V
		configVal |= nrf.SAADC_CH_CONFIG_GAIN_Gain4 << nrf.SAADC_CH_CONFIG_GAIN_Pos
	case 300: // 0.3V
		configVal |= nrf.SAADC_CH_CONFIG_GAIN_Gain2 << nrf.SAADC_CH_CONFIG_GAIN_Pos
	case 600: // 0.6V
		configVal |= nrf.SAADC_CH_CONFIG_GAIN_Gain1 << nrf.SAADC_CH_CONFIG_GAIN_Pos
	case 1200: // 1.2V
		configVal |= nrf.SAADC_CH_CONFIG_GAIN_Gain1_2 << nrf.SAADC_CH_CONFIG_GAIN_Pos
	case 1800: // 1.8V
		configVal |= nrf.SAADC_CH_CONFIG_GAIN_Gain1_3 << nrf.SAADC_CH_CONFIG_GAIN_Pos
	case 2400: // 2.4V
		configVal |= nrf.SAADC_CH_CONFIG_GAIN_Gain1_4 << nrf.SAADC_CH_CONFIG_GAIN_Pos
	case 3000, 0: // 3.0V (default)
		configVal |= nrf.SAADC_CH_CONFIG_GAIN_Gain1_5 << nrf.SAADC_CH_CONFIG_GAIN_Pos
	case 3600: // 3.6V
		configVal |= nrf.SAADC_CH_CONFIG_GAIN_Gain1_6 << nrf.SAADC_CH_CONFIG_GAIN_Pos
	default:
		// TODO: return an error, will that interfere with any interfaced if one will be?
	}

	var resolution uint32
	switch config.Resolution {
	case 8:
		resolution = nrf.SAADC_RESOLUTION_VAL_8bit
	case 10:
		resolution = nrf.SAADC_RESOLUTION_VAL_10bit
	case 12:
		resolution = nrf.SAADC_RESOLUTION_VAL_12bit
	case 14:
		resolution = nrf.SAADC_RESOLUTION_VAL_14bit
	default:
		resolution = nrf.SAADC_RESOLUTION_VAL_12bit
	}
	nrf.SAADC.RESOLUTION.Set(resolution)

	// Source resistance, according to table 41 on page 676 of the nrf52832 datasheet.
	// https://docs-be.nordicsemi.com/bundle/ps_nrf52840/attach/nRF52840_PS_v1.11.pdf?_LANG=enus
	if config.SampleTime <= 3 { // <= 10kΩ
		configVal |= nrf.SAADC_CH_CONFIG_TACQ_3us << nrf.SAADC_CH_CONFIG_TACQ_Pos
	} else if config.SampleTime <= 5 { // <= 40kΩ
		configVal |= nrf.SAADC_CH_CONFIG_TACQ_5us << nrf.SAADC_CH_CONFIG_TACQ_Pos
	} else if config.SampleTime <= 10 { // <= 100kΩ
		configVal |= nrf.SAADC_CH_CONFIG_TACQ_10us << nrf.SAADC_CH_CONFIG_TACQ_Pos
	} else if config.SampleTime <= 15 { // <= 200kΩ
		configVal |= nrf.SAADC_CH_CONFIG_TACQ_15us << nrf.SAADC_CH_CONFIG_TACQ_Pos
	} else if config.SampleTime <= 20 { // <= 400kΩ
		configVal |= nrf.SAADC_CH_CONFIG_TACQ_20us << nrf.SAADC_CH_CONFIG_TACQ_Pos
	} else { // <= 800kΩ
		configVal |= nrf.SAADC_CH_CONFIG_TACQ_40us << nrf.SAADC_CH_CONFIG_TACQ_Pos
	}

	// Oversampling configuration.
	burst := true
	switch config.Samples {
	default: // no oversampling
		nrf.SAADC.OVERSAMPLE.Set(nrf.SAADC_OVERSAMPLE_OVERSAMPLE_Bypass)
		burst = false
	case 2:
		nrf.SAADC.OVERSAMPLE.Set(nrf.SAADC_OVERSAMPLE_OVERSAMPLE_Over2x)
	case 4:
		nrf.SAADC.OVERSAMPLE.Set(nrf.SAADC_OVERSAMPLE_OVERSAMPLE_Over4x)
	case 8:
		nrf.SAADC.OVERSAMPLE.Set(nrf.SAADC_OVERSAMPLE_OVERSAMPLE_Over8x)
	case 16:
		nrf.SAADC.OVERSAMPLE.Set(nrf.SAADC_OVERSAMPLE_OVERSAMPLE_Over16x)
	case 32:
		nrf.SAADC.OVERSAMPLE.Set(nrf.SAADC_OVERSAMPLE_OVERSAMPLE_Over32x)
	case 64:
		nrf.SAADC.OVERSAMPLE.Set(nrf.SAADC_OVERSAMPLE_OVERSAMPLE_Over64x)
	case 128:
		nrf.SAADC.OVERSAMPLE.Set(nrf.SAADC_OVERSAMPLE_OVERSAMPLE_Over128x)
	case 256:
		nrf.SAADC.OVERSAMPLE.Set(nrf.SAADC_OVERSAMPLE_OVERSAMPLE_Over256x)
	}
	if burst {
		// BURST=1 is needed when oversampling
		configVal |= nrf.SAADC_CH_CONFIG_BURST
	}

	// Configure channel 0, which is the only channel we use.
	nrf.SAADC.CH[0].CONFIG.Set(configVal)
}

// Get returns the current value of an ADC pin in the range 0..0xffff.
func (a *ADC) Get() uint16 {
	var adcPin uint32
	var rawValue volatile.Register16

	switch a.Pin {
	case 2:
		adcPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput0
	case 3:
		adcPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput1
	case 4:
		adcPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput2
	case 5:
		adcPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput3
	case 28:
		adcPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput4
	case 29:
		adcPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput5
	case 30:
		adcPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput6
	case 31:
		adcPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput7
	case adcVDDHPin:
		if Device == "nrf52840" {
			adcPin = 0x0D // VDDHDIV5 on the nrf52840
		} else {
			return 0
		}
	default:
		return 0
	}

	// Set pin to read.
	nrf.SAADC.CH[0].PSELP.Set(adcPin)

	// Destination for sample result.
	// Note: rawValue doesn't need to be kept alive for the GC, since the
	// volatile read later will force it to stay alive.
	nrf.SAADC.RESULT.PTR.Set(uint32(unsafeNoEscape(unsafe.Pointer(&rawValue))))
	nrf.SAADC.RESULT.MAXCNT.Set(1) // One sample

	// Start tasks.
	nrf.SAADC.TASKS_START.Set(1)
	for nrf.SAADC.EVENTS_STARTED.Get() == 0 {
	}
	nrf.SAADC.EVENTS_STARTED.Set(0x00)

	// Start the sample task.
	nrf.SAADC.TASKS_SAMPLE.Set(1)

	// Wait until the sample task is done.
	for nrf.SAADC.EVENTS_END.Get() == 0 {
	}
	nrf.SAADC.EVENTS_END.Set(0x00)

	// Stop the ADC
	nrf.SAADC.TASKS_STOP.Set(1)
	for nrf.SAADC.EVENTS_STOPPED.Get() == 0 {
	}
	nrf.SAADC.EVENTS_STOPPED.Set(0)

	// convert to 16 bit resolution/value
	var resolutionAdjustment uint8
	switch nrf.SAADC.RESOLUTION.Get() {
	case nrf.SAADC_RESOLUTION_VAL_8bit:
		resolutionAdjustment = 8
	case nrf.SAADC_RESOLUTION_VAL_10bit:
		resolutionAdjustment = 6
	case nrf.SAADC_RESOLUTION_VAL_12bit:
		resolutionAdjustment = 4
	case nrf.SAADC_RESOLUTION_VAL_14bit:
		resolutionAdjustment = 2
	default:
		resolutionAdjustment = 4 // 12bit
	}

	value := int16(rawValue.Get())
	if value < 0 {
		value = 0
	}

	return uint16(value << resolutionAdjustment)
}

// SPI on the NRF.
type SPI struct {
	Bus *nrf.SPIM_Type
	buf *[1]byte // 1-byte buffer for the Transfer method
}

// There are 3 SPI interfaces on the NRF528xx.
var (
	SPI0 = &SPI{Bus: nrf.SPIM0, buf: new([1]byte)}
	SPI1 = &SPI{Bus: nrf.SPIM1, buf: new([1]byte)}
	SPI2 = &SPI{Bus: nrf.SPIM2, buf: new([1]byte)}
)

// SPIConfig is used to store config info for SPI.
type SPIConfig struct {
	Frequency uint32
	SCK       Pin
	SDO       Pin
	SDI       Pin
	LSBFirst  bool
	Mode      uint8
}

// Configure is intended to set up the SPI interface.
func (spi *SPI) Configure(config SPIConfig) error {
	// Disable bus to configure it
	spi.Bus.ENABLE.Set(nrf.SPIM_ENABLE_ENABLE_Disabled)

	// Pick a default frequency.
	if config.Frequency == 0 {
		config.Frequency = 4000000 // 4MHz
	}

	// set frequency
	var freq uint32
	switch {
	case config.Frequency >= 8000000:
		freq = nrf.SPIM_FREQUENCY_FREQUENCY_M8
	case config.Frequency >= 4000000:
		freq = nrf.SPIM_FREQUENCY_FREQUENCY_M4
	case config.Frequency >= 2000000:
		freq = nrf.SPIM_FREQUENCY_FREQUENCY_M2
	case config.Frequency >= 1000000:
		freq = nrf.SPIM_FREQUENCY_FREQUENCY_M1
	case config.Frequency >= 500000:
		freq = nrf.SPIM_FREQUENCY_FREQUENCY_K500
	case config.Frequency >= 250000:
		freq = nrf.SPIM_FREQUENCY_FREQUENCY_K250
	default: // below 250kHz, default to the lowest speed available
		freq = nrf.SPIM_FREQUENCY_FREQUENCY_K125
	}
	spi.Bus.FREQUENCY.Set(freq)

	var conf uint32

	// set bit transfer order
	if config.LSBFirst {
		conf = (nrf.SPIM_CONFIG_ORDER_LsbFirst << nrf.SPIM_CONFIG_ORDER_Pos)
	}

	// set mode
	switch config.Mode {
	case 0:
		conf &^= (nrf.SPIM_CONFIG_CPOL_ActiveHigh << nrf.SPIM_CONFIG_CPOL_Pos)
		conf &^= (nrf.SPIM_CONFIG_CPHA_Leading << nrf.SPIM_CONFIG_CPHA_Pos)
	case 1:
		conf &^= (nrf.SPIM_CONFIG_CPOL_ActiveHigh << nrf.SPIM_CONFIG_CPOL_Pos)
		conf |= (nrf.SPIM_CONFIG_CPHA_Trailing << nrf.SPIM_CONFIG_CPHA_Pos)
	case 2:
		conf |= (nrf.SPIM_CONFIG_CPOL_ActiveLow << nrf.SPIM_CONFIG_CPOL_Pos)
		conf &^= (nrf.SPIM_CONFIG_CPHA_Leading << nrf.SPIM_CONFIG_CPHA_Pos)
	case 3:
		conf |= (nrf.SPIM_CONFIG_CPOL_ActiveLow << nrf.SPIM_CONFIG_CPOL_Pos)
		conf |= (nrf.SPIM_CONFIG_CPHA_Trailing << nrf.SPIM_CONFIG_CPHA_Pos)
	default: // to mode
		conf &^= (nrf.SPIM_CONFIG_CPOL_ActiveHigh << nrf.SPIM_CONFIG_CPOL_Pos)
		conf &^= (nrf.SPIM_CONFIG_CPHA_Leading << nrf.SPIM_CONFIG_CPHA_Pos)
	}
	spi.Bus.CONFIG.Set(conf)

	// set pins
	if config.SCK == 0 && config.SDO == 0 && config.SDI == 0 {
		config.SCK = SPI0_SCK_PIN
		config.SDO = SPI0_SDO_PIN
		config.SDI = SPI0_SDI_PIN
	}
	spi.Bus.PSEL.SCK.Set(uint32(config.SCK))
	spi.Bus.PSEL.MOSI.Set(uint32(config.SDO))
	spi.Bus.PSEL.MISO.Set(uint32(config.SDI))

	// Re-enable bus now that it is configured.
	spi.Bus.ENABLE.Set(nrf.SPIM_ENABLE_ENABLE_Enabled)

	return nil
}

// Transfer writes/reads a single byte using the SPI interface.
func (spi *SPI) Transfer(w byte) (byte, error) {
	buf := spi.buf[:]
	buf[0] = w
	err := spi.Tx(buf[:], buf[:])
	return buf[0], err
}

// Tx handles read/write operation for SPI interface. Since SPI is a synchronous
// write/read interface, there must always be the same number of bytes written
// as bytes read. Therefore, if the number of bytes don't match it will be
// padded until they fit: if len(w) > len(r) the extra bytes received will be
// dropped and if len(w) < len(r) extra 0 bytes will be sent.
func (spi *SPI) Tx(w, r []byte) error {
	// Unfortunately the hardware (on the nrf52832) only supports a limited
	// amount of bytes in the buffers (depending on the chip), so if either w or
	// r is longer than that the transfer needs to be broken up in pieces.
	for len(r) != 0 || len(w) != 0 {
		// Prepare the SPI transfer: set the DMA pointers and lengths.
		// read buffer
		nr := uint32(len(r))
		if nr > 0 {
			if nr > spiMaxBufferSize {
				nr = spiMaxBufferSize
			}
			spi.Bus.RXD.PTR.Set(uint32(unsafeNoEscape(unsafe.Pointer(unsafe.SliceData(r)))))
			r = r[nr:]
		}
		spi.Bus.RXD.MAXCNT.Set(nr)

		// write buffer
		nw := uint32(len(w))
		if nw > 0 {
			if nw > spiMaxBufferSize {
				nw = spiMaxBufferSize
			}
			spi.Bus.TXD.PTR.Set(uint32(unsafeNoEscape(unsafe.Pointer(unsafe.SliceData(w)))))
			w = w[nw:]
		}
		spi.Bus.TXD.MAXCNT.Set(nw)

		// Do the transfer.
		// Note: this can be improved by not waiting until the transfer is
		// finished if the transfer is send-only (a common case).
		spi.Bus.TASKS_START.Set(1)
		for spi.Bus.EVENTS_END.Get() == 0 {
			gosched()
		}
		spi.Bus.EVENTS_END.Set(0)
	}

	// Make sure the w and r buffers stay alive for the GC until this point,
	// since they are used by the hardware but not otherwise visible.
	keepAliveNoEscape(unsafe.Pointer(unsafe.SliceData(r)))
	keepAliveNoEscape(unsafe.Pointer(unsafe.SliceData(w)))

	return nil
}

// PWM is one PWM peripheral, which consists of a counter and multiple output
// channels (that can be connected to actual pins). You can set the frequency
// using SetPeriod, but only for all the channels in this PWM peripheral at
// once.
type PWM struct {
	PWM *nrf.PWM_Type

	channelValues [4]volatile.Register16
}

// Configure enables and configures this PWM.
// On the nRF52 series, the maximum period is around 0.26s.
func (pwm *PWM) Configure(config PWMConfig) error {
	// Enable the peripheral.
	pwm.PWM.ENABLE.Set(nrf.PWM_ENABLE_ENABLE_Enabled << nrf.PWM_ENABLE_ENABLE_Pos)

	// Use up counting only. TODO: allow configuring as up-and-down.
	pwm.PWM.MODE.Set(nrf.PWM_MODE_UPDOWN_Up << nrf.PWM_MODE_UPDOWN_Pos)

	// Indicate there are four channels that each have a different value.
	pwm.PWM.DECODER.Set(nrf.PWM_DECODER_LOAD_Individual<<nrf.PWM_DECODER_LOAD_Pos | nrf.PWM_DECODER_MODE_RefreshCount<<nrf.PWM_DECODER_MODE_Pos)

	err := pwm.setPeriod(config.Period, true)
	if err != nil {
		return err
	}

	// Set the EasyDMA buffer, which has 4 values (one for each channel).
	pwm.PWM.SEQ[0].PTR.Set(uint32(uintptr(unsafe.Pointer(&pwm.channelValues[0]))))
	pwm.PWM.SEQ[0].CNT.Set(4)

	// SEQ[0] is not yet started, it will be started on the first
	// PWMChannel.Set() call.

	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 {
	return pwm.setPeriod(period, false)
}

func (pwm *PWM) setPeriod(period uint64, updatePrescaler bool) error {
	const maxTop = 0x7fff // 15 bits counter

	// The top value is the number of PWM ticks a PWM period takes. It is
	// initially picked assuming an unlimited COUNTERTOP and no PWM prescaler.
	var top uint64
	if period == 0 {
		// The period is 0, which means "pick something reasonable for LEDs".
		top = maxTop
	} else {
		// The formula below calculates the following formula, optimized:
		//     period * (16e6 / 1e9)
		// The max frequency (16e6 or 16MHz) is set by the hardware.
		top = period * 2 / 125
	}

	// The ideal PWM period may be larger than would fit in the PWM counter,
	// which is only 15 bits (see maxTop). Therefore, try to make the PWM clock
	// speed lower with a prescaler to make the top value fit the COUNTERTOP.
	if updatePrescaler {
		// This function was called during Configure().
		switch {
		case top <= maxTop:
			pwm.PWM.PRESCALER.Set(nrf.PWM_PRESCALER_PRESCALER_DIV_1)
		case top/2 <= maxTop:
			pwm.PWM.PRESCALER.Set(nrf.PWM_PRESCALER_PRESCALER_DIV_2)
			top /= 2
		case top/4 <= maxTop:
			pwm.PWM.PRESCALER.Set(nrf.PWM_PRESCALER_PRESCALER_DIV_4)
			top /= 4
		case top/8 <= maxTop:
			pwm.PWM.PRESCALER.Set(nrf.PWM_PRESCALER_PRESCALER_DIV_8)
			top /= 8
		case top/16 <= maxTop:
			pwm.PWM.PRESCALER.Set(nrf.PWM_PRESCALER_PRESCALER_DIV_16)
			top /= 16
		case top/32 <= maxTop:
			pwm.PWM.PRESCALER.Set(nrf.PWM_PRESCALER_PRESCALER_DIV_32)
			top /= 32
		case top/64 <= maxTop:
			pwm.PWM.PRESCALER.Set(nrf.PWM_PRESCALER_PRESCALER_DIV_64)
			top /= 64
		case top/128 <= maxTop:
			pwm.PWM.PRESCALER.Set(nrf.PWM_PRESCALER_PRESCALER_DIV_128)
			top /= 128
		default:
			return ErrPWMPeriodTooLong
		}
	} else {
		// Do not update the prescaler, but use the already-configured
		// prescaler. This is the normal SetPeriod case, where the prescaler
		// must not be changed.
		prescaler := pwm.PWM.PRESCALER.Get()
		switch prescaler {
		case nrf.PWM_PRESCALER_PRESCALER_DIV_1:
			top /= 1
		case nrf.PWM_PRESCALER_PRESCALER_DIV_2:
			top /= 2
		case nrf.PWM_PRESCALER_PRESCALER_DIV_4:
			top /= 4
		case nrf.PWM_PRESCALER_PRESCALER_DIV_8:
			top /= 8
		case nrf.PWM_PRESCALER_PRESCALER_DIV_16:
			top /= 16
		case nrf.PWM_PRESCALER_PRESCALER_DIV_32:
			top /= 32
		case nrf.PWM_PRESCALER_PRESCALER_DIV_64:
			top /= 64
		case nrf.PWM_PRESCALER_PRESCALER_DIV_128:
			top /= 128
		}
		if top > maxTop {
			return ErrPWMPeriodTooLong
		}
	}
	pwm.PWM.COUNTERTOP.Set(uint32(top))

	// Apparently this is needed to apply the new COUNTERTOP.
	pwm.PWM.TASKS_SEQSTART[0].Set(1)

	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
// pwm.Set (see pwm.Set for more information).
func (pwm *PWM) Top() uint32 {
	return pwm.PWM.COUNTERTOP.Get()
}

// Channel returns a PWM channel for the given pin.
func (pwm *PWM) Channel(pin Pin) (uint8, error) {
	config := uint32(pin)
	for ch := uint8(0); ch < 4; ch++ {
		channelConfig := pwm.PWM.PSEL.OUT[ch].Get()
		if channelConfig == 0xffffffff {
			// Unused channel. Configure it.
			pwm.PWM.PSEL.OUT[ch].Set(config)
			// Configure the pin (required by the reference manual).
			pin.Configure(PinConfig{Mode: PinOutput})
			// Set channel to zero and non-inverting.
			pwm.channelValues[ch].Set(0x8000)
			return ch, nil
		} else if channelConfig == config {
			// This channel is already configured for this pin.
			return ch, nil
		}
	}

	// All four pins are already in use with other pins.
	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) {
	ptr := &pwm.channelValues[channel]
	if inverting {
		ptr.Set(ptr.Get() &^ 0x8000)
	} else {
		ptr.Set(ptr.Get() | 0x8000)
	}
}

// Set updates the channel value. This is used to control the channel duty
// cycle. For example, to set it to a 25% duty cycle, use:
//
//	ch.Set(ch.Top() / 4)
//
// ch.Set(0) will set the output to low and ch.Set(ch.Top()) will set the output
// to high, assuming the output isn't inverted.
func (pwm *PWM) Set(channel uint8, value uint32) {
	// Update the channel value while retaining the polarity bit.
	ptr := &pwm.channelValues[channel]
	ptr.Set(ptr.Get()&0x8000 | uint16(value)&0x7fff)

	// Start the PWM, if it isn't already running.
	pwm.PWM.TASKS_SEQSTART[0].Set(1)
}
