nrf: refactor code a bit to reduce duplication

The nrf52 series is all very similar and copying the code only makes it
harder to maintain the code or to add more chips in the nrf52 series
(for example, the nrf52833 as used in the micro:bit v2).

This commit also has a small improvement regarding pins: it now includes
chip-level pin names (P0.00, P0.01, etc) to the machine package.

3 files changed, 203 insertions, 321 deletions

diff --git a/src/machine/machine_nrf52.go b/src/machine/machine_nrf52.go
index 880126a11..189f0a32a 100644
--- a/src/machine/machine_nrf52.go
+++ b/src/machine/machine_nrf52.go
@@ -4,17 +4,48 @@ package machine
 
 import (
 	"device/nrf"
-	"unsafe"
+)
+
+// Hardware pins
+const (
+	P0_00 Pin = 0
+	P0_01 Pin = 1
+	P0_02 Pin = 2
+	P0_03 Pin = 3
+	P0_04 Pin = 4
+	P0_05 Pin = 5
+	P0_06 Pin = 6
+	P0_07 Pin = 7
+	P0_08 Pin = 8
+	P0_09 Pin = 9
+	P0_10 Pin = 10
+	P0_11 Pin = 11
+	P0_12 Pin = 12
+	P0_13 Pin = 13
+	P0_14 Pin = 14
+	P0_15 Pin = 15
+	P0_16 Pin = 16
+	P0_17 Pin = 17
+	P0_18 Pin = 18
+	P0_19 Pin = 19
+	P0_20 Pin = 20
+	P0_21 Pin = 21
+	P0_22 Pin = 22
+	P0_23 Pin = 23
+	P0_24 Pin = 24
+	P0_25 Pin = 25
+	P0_26 Pin = 26
+	P0_27 Pin = 27
+	P0_28 Pin = 28
+	P0_29 Pin = 29
+	P0_30 Pin = 30
+	P0_31 Pin = 31
 )
 
 var (
 	UART0 = NRF_UART0
 )
 
-func CPUFrequency() uint32 {
-	return 64000000
-}
-
 // Get peripheral and pin number for this GPIO pin.
 func (p Pin) getPortPin() (*nrf.GPIO_Type, uint32) {
 	return nrf.P0, uint32(p)
@@ -30,165 +61,9 @@ func (i2c I2C) setPins(scl, sda Pin) {
 	i2c.Bus.PSELSDA.Set(uint32(sda))
 }
 
-// SPI
-func (spi SPI) setPins(sck, sdo, sdi Pin) {
-	if sck == 0 {
-		sck = SPI0_SCK_PIN
-	}
-	if sdo == 0 {
-		sdo = SPI0_SDO_PIN
-	}
-	if sdi == 0 {
-		sdi = SPI0_SDI_PIN
-	}
-	spi.Bus.PSEL.SCK.Set(uint32(sck))
-	spi.Bus.PSEL.MOSI.Set(uint32(sdo))
-	spi.Bus.PSEL.MISO.Set(uint32(sdi))
-}
-
-// InitADC initializes the registers needed for ADC.
-func InitADC() {
-	return // no specific setup on nrf52 machine.
-}
-
-// Configure configures an ADC pin to be able to read analog data.
-func (a ADC) Configure() {
-	return // no pin specific setup on nrf52 machine.
-}
-
-// Get returns the current value of a ADC pin in the range 0..0xffff.
-func (a ADC) Get() uint16 {
-	var pwmPin uint32
-	var value int16
-
-	switch a.Pin {
-	case 2:
-		pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput0
-
-	case 3:
-		pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput1
-
-	case 4:
-		pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput2
-
-	case 5:
-		pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput3
-
-	case 28:
-		pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput4
-
-	case 29:
-		pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput5
-
-	case 30:
-		pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput6
-
-	case 31:
-		pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput7
-
-	default:
-		return 0
-	}
-
-	nrf.SAADC.RESOLUTION.Set(nrf.SAADC_RESOLUTION_VAL_12bit)
-
-	// Enable ADC.
-	nrf.SAADC.ENABLE.Set(nrf.SAADC_ENABLE_ENABLE_Enabled << nrf.SAADC_ENABLE_ENABLE_Pos)
-	for i := 0; i < 8; i++ {
-		nrf.SAADC.CH[i].PSELN.Set(nrf.SAADC_CH_PSELP_PSELP_NC)
-		nrf.SAADC.CH[i].PSELP.Set(nrf.SAADC_CH_PSELP_PSELP_NC)
-	}
-
-	// Configure ADC.
-	nrf.SAADC.CH[0].CONFIG.Set(((nrf.SAADC_CH_CONFIG_RESP_Bypass << nrf.SAADC_CH_CONFIG_RESP_Pos) & nrf.SAADC_CH_CONFIG_RESP_Msk) |
-		((nrf.SAADC_CH_CONFIG_RESP_Bypass << nrf.SAADC_CH_CONFIG_RESN_Pos) & nrf.SAADC_CH_CONFIG_RESN_Msk) |
-		((nrf.SAADC_CH_CONFIG_GAIN_Gain1_5 << nrf.SAADC_CH_CONFIG_GAIN_Pos) & nrf.SAADC_CH_CONFIG_GAIN_Msk) |
-		((nrf.SAADC_CH_CONFIG_REFSEL_Internal << nrf.SAADC_CH_CONFIG_REFSEL_Pos) & nrf.SAADC_CH_CONFIG_REFSEL_Msk) |
-		((nrf.SAADC_CH_CONFIG_TACQ_3us << nrf.SAADC_CH_CONFIG_TACQ_Pos) & nrf.SAADC_CH_CONFIG_TACQ_Msk) |
-		((nrf.SAADC_CH_CONFIG_MODE_SE << nrf.SAADC_CH_CONFIG_MODE_Pos) & nrf.SAADC_CH_CONFIG_MODE_Msk))
-
-	// Set pin to read.
-	nrf.SAADC.CH[0].PSELN.Set(pwmPin)
-	nrf.SAADC.CH[0].PSELP.Set(pwmPin)
-
-	// Destination for sample result.
-	nrf.SAADC.RESULT.PTR.Set(uint32(uintptr(unsafe.Pointer(&value))))
-	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)
-
-	// Disable the ADC.
-	nrf.SAADC.ENABLE.Set(nrf.SAADC_ENABLE_ENABLE_Disabled << nrf.SAADC_ENABLE_ENABLE_Pos)
-
-	if value < 0 {
-		value = 0
-	}
-
-	// Return 16-bit result from 12-bit value.
-	return uint16(value << 4)
-}
-
 // PWM
 var (
 	pwmChannelPins     = [3]uint32{0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF}
 	pwms               = [3]*nrf.PWM_Type{nrf.PWM0, nrf.PWM1, nrf.PWM2}
 	pwmChannelSequence [3]uint16
 )
-
-// InitPWM initializes the registers needed for PWM.
-func InitPWM() {
-	return
-}
-
-// Configure configures a PWM pin for output.
-func (pwm PWM) Configure() error {
-	return nil
-}
-
-// Set turns on the duty cycle for a PWM pin using the provided value.
-func (pwm PWM) Set(value uint16) {
-	for i := 0; i < 3; i++ {
-		if pwmChannelPins[i] == 0xFFFFFFFF || pwmChannelPins[i] == uint32(pwm.Pin) {
-			pwmChannelPins[i] = uint32(pwm.Pin)
-			pwmChannelSequence[i] = (value >> 2) | 0x8000 // set bit 15 to invert polarity
-
-			p := pwms[i]
-
-			p.PSEL.OUT[0].Set(uint32(pwm.Pin))
-			p.PSEL.OUT[1].Set(uint32(pwm.Pin))
-			p.PSEL.OUT[2].Set(uint32(pwm.Pin))
-			p.PSEL.OUT[3].Set(uint32(pwm.Pin))
-			p.ENABLE.Set(nrf.PWM_ENABLE_ENABLE_Enabled << nrf.PWM_ENABLE_ENABLE_Pos)
-			p.PRESCALER.Set(nrf.PWM_PRESCALER_PRESCALER_DIV_2)
-			p.MODE.Set(nrf.PWM_MODE_UPDOWN_Up)
-			p.COUNTERTOP.Set(16384) // frequency
-			p.LOOP.Set(0)
-			p.DECODER.Set((nrf.PWM_DECODER_LOAD_Common << nrf.PWM_DECODER_LOAD_Pos) | (nrf.PWM_DECODER_MODE_RefreshCount << nrf.PWM_DECODER_MODE_Pos))
-			p.SEQ[0].PTR.Set(uint32(uintptr(unsafe.Pointer(&pwmChannelSequence[i]))))
-			p.SEQ[0].CNT.Set(1)
-			p.SEQ[0].REFRESH.Set(1)
-			p.SEQ[0].ENDDELAY.Set(0)
-			p.TASKS_SEQSTART[0].Set(1)
-
-			break
-		}
-	}
-}
diff --git a/src/machine/machine_nrf52840.go b/src/machine/machine_nrf52840.go
index 7afb9286e..157495dc1 100644
--- a/src/machine/machine_nrf52840.go
+++ b/src/machine/machine_nrf52840.go
@@ -4,13 +4,8 @@ package machine
 
 import (
 	"device/nrf"
-	"unsafe"
 )
 
-func CPUFrequency() uint32 {
-	return 64000000
-}
-
 // Hardware pins
 const (
 	P0_00 Pin = 0
@@ -82,164 +77,9 @@ func (i2c I2C) setPins(scl, sda Pin) {
 	i2c.Bus.PSEL.SDA.Set(uint32(sda))
 }
 
-// SPI
-func (spi SPI) setPins(sck, sdo, sdi Pin) {
-	if sck == 0 {
-		sck = SPI0_SCK_PIN
-	}
-	if sdo == 0 {
-		sdo = SPI0_SDO_PIN
-	}
-	if sdi == 0 {
-		sdi = SPI0_SDI_PIN
-	}
-	spi.Bus.PSEL.SCK.Set(uint32(sck))
-	spi.Bus.PSEL.MOSI.Set(uint32(sdo))
-	spi.Bus.PSEL.MISO.Set(uint32(sdi))
-}
-
-// InitADC initializes the registers needed for ADC.
-func InitADC() {
-	return // no specific setup on nrf52840 machine.
-}
-
-// Configure configures an ADC pin to be able to read analog data.
-func (a ADC) Configure() error {
-	return nil // no pin specific setup on nrf52840 machine.
-}
-
-// Get returns the current value of a ADC pin in the range 0..0xffff.
-func (a ADC) Get() uint16 {
-	var pwmPin uint32
-	var value int16
-
-	switch a.Pin {
-	case 2:
-		pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput0
-
-	case 3:
-		pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput1
-
-	case 4:
-		pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput2
-
-	case 5:
-		pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput3
-
-	case 28:
-		pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput4
-
-	case 29:
-		pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput5
-
-	case 30:
-		pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput6
-
-	case 31:
-		pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput7
-
-	default:
-		return 0
-	}
-
-	nrf.SAADC.RESOLUTION.Set(nrf.SAADC_RESOLUTION_VAL_12bit)
-
-	// Enable ADC.
-	nrf.SAADC.ENABLE.Set(nrf.SAADC_ENABLE_ENABLE_Enabled << nrf.SAADC_ENABLE_ENABLE_Pos)
-	for i := 0; i < 8; i++ {
-		nrf.SAADC.CH[i].PSELN.Set(nrf.SAADC_CH_PSELP_PSELP_NC)
-		nrf.SAADC.CH[i].PSELP.Set(nrf.SAADC_CH_PSELP_PSELP_NC)
-	}
-
-	// Configure ADC.
-	nrf.SAADC.CH[0].CONFIG.Set(((nrf.SAADC_CH_CONFIG_RESP_Bypass << nrf.SAADC_CH_CONFIG_RESP_Pos) & nrf.SAADC_CH_CONFIG_RESP_Msk) |
-		((nrf.SAADC_CH_CONFIG_RESP_Bypass << nrf.SAADC_CH_CONFIG_RESN_Pos) & nrf.SAADC_CH_CONFIG_RESN_Msk) |
-		((nrf.SAADC_CH_CONFIG_GAIN_Gain1_5 << nrf.SAADC_CH_CONFIG_GAIN_Pos) & nrf.SAADC_CH_CONFIG_GAIN_Msk) |
-		((nrf.SAADC_CH_CONFIG_REFSEL_Internal << nrf.SAADC_CH_CONFIG_REFSEL_Pos) & nrf.SAADC_CH_CONFIG_REFSEL_Msk) |
-		((nrf.SAADC_CH_CONFIG_TACQ_3us << nrf.SAADC_CH_CONFIG_TACQ_Pos) & nrf.SAADC_CH_CONFIG_TACQ_Msk) |
-		((nrf.SAADC_CH_CONFIG_MODE_SE << nrf.SAADC_CH_CONFIG_MODE_Pos) & nrf.SAADC_CH_CONFIG_MODE_Msk))
-
-	// Set pin to read.
-	nrf.SAADC.CH[0].PSELN.Set(pwmPin)
-	nrf.SAADC.CH[0].PSELP.Set(pwmPin)
-
-	// Destination for sample result.
-	nrf.SAADC.RESULT.PTR.Set(uint32(uintptr(unsafe.Pointer(&value))))
-	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)
-
-	// Disable the ADC.
-	nrf.SAADC.ENABLE.Set(nrf.SAADC_ENABLE_ENABLE_Disabled << nrf.SAADC_ENABLE_ENABLE_Pos)
-
-	if value < 0 {
-		value = 0
-	}
-
-	// Return 16-bit result from 12-bit value.
-	return uint16(value << 4)
-}
-
 // PWM
 var (
 	pwmChannelPins     = [4]uint32{0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF}
 	pwms               = [4]*nrf.PWM_Type{nrf.PWM0, nrf.PWM1, nrf.PWM2, nrf.PWM3}
 	pwmChannelSequence [4]uint16
 )
-
-// InitPWM initializes the registers needed for PWM.
-func InitPWM() {
-	return
-}
-
-// Configure configures a PWM pin for output.
-func (pwm PWM) Configure() {
-}
-
-// Set turns on the duty cycle for a PWM pin using the provided value.
-func (pwm PWM) Set(value uint16) {
-	for i := 0; i < 4; i++ {
-		if pwmChannelPins[i] == 0xFFFFFFFF || pwmChannelPins[i] == uint32(pwm.Pin) {
-			pwmChannelPins[i] = uint32(pwm.Pin)
-			pwmChannelSequence[i] = (value >> 2) | 0x8000 // set bit 15 to invert polarity
-
-			p := pwms[i]
-
-			p.PSEL.OUT[0].Set(uint32(pwm.Pin))
-			p.PSEL.OUT[1].Set(uint32(pwm.Pin))
-			p.PSEL.OUT[2].Set(uint32(pwm.Pin))
-			p.PSEL.OUT[3].Set(uint32(pwm.Pin))
-			p.ENABLE.Set(nrf.PWM_ENABLE_ENABLE_Enabled << nrf.PWM_ENABLE_ENABLE_Pos)
-			p.PRESCALER.Set(nrf.PWM_PRESCALER_PRESCALER_DIV_2)
-			p.MODE.Set(nrf.PWM_MODE_UPDOWN_Up)
-			p.COUNTERTOP.Set(16384) // frequency
-			p.LOOP.Set(0)
-			p.DECODER.Set((nrf.PWM_DECODER_LOAD_Common << nrf.PWM_DECODER_LOAD_Pos) | (nrf.PWM_DECODER_MODE_RefreshCount << nrf.PWM_DECODER_MODE_Pos))
-			p.SEQ[0].PTR.Set(uint32(uintptr(unsafe.Pointer(&pwmChannelSequence[i]))))
-			p.SEQ[0].CNT.Set(1)
-			p.SEQ[0].REFRESH.Set(1)
-			p.SEQ[0].ENDDELAY.Set(0)
-			p.TASKS_SEQSTART[0].Set(1)
-
-			break
-		}
-	}
-}
diff --git a/src/machine/machine_nrf528xx.go b/src/machine/machine_nrf528xx.go
new file mode 100644
index 000000000..2a207580f
--- /dev/null
+++ b/src/machine/machine_nrf528xx.go
@@ -0,0 +1,167 @@
+// +build nrf52 nrf52840
+
+package machine
+
+import (
+	"device/nrf"
+	"unsafe"
+)
+
+func CPUFrequency() uint32 {
+	return 64000000
+}
+
+// InitADC initializes the registers needed for ADC.
+func InitADC() {
+	return // no specific setup on nrf52 machine.
+}
+
+// Configure configures an ADC pin to be able to read analog data.
+func (a ADC) Configure() {
+	return // no pin specific setup on nrf52 machine.
+}
+
+// Get returns the current value of a ADC pin in the range 0..0xffff.
+func (a ADC) Get() uint16 {
+	var pwmPin uint32
+	var value int16
+
+	switch a.Pin {
+	case 2:
+		pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput0
+
+	case 3:
+		pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput1
+
+	case 4:
+		pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput2
+
+	case 5:
+		pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput3
+
+	case 28:
+		pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput4
+
+	case 29:
+		pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput5
+
+	case 30:
+		pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput6
+
+	case 31:
+		pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput7
+
+	default:
+		return 0
+	}
+
+	nrf.SAADC.RESOLUTION.Set(nrf.SAADC_RESOLUTION_VAL_12bit)
+
+	// Enable ADC.
+	nrf.SAADC.ENABLE.Set(nrf.SAADC_ENABLE_ENABLE_Enabled << nrf.SAADC_ENABLE_ENABLE_Pos)
+	for i := 0; i < 8; i++ {
+		nrf.SAADC.CH[i].PSELN.Set(nrf.SAADC_CH_PSELP_PSELP_NC)
+		nrf.SAADC.CH[i].PSELP.Set(nrf.SAADC_CH_PSELP_PSELP_NC)
+	}
+
+	// Configure ADC.
+	nrf.SAADC.CH[0].CONFIG.Set(((nrf.SAADC_CH_CONFIG_RESP_Bypass << nrf.SAADC_CH_CONFIG_RESP_Pos) & nrf.SAADC_CH_CONFIG_RESP_Msk) |
+		((nrf.SAADC_CH_CONFIG_RESP_Bypass << nrf.SAADC_CH_CONFIG_RESN_Pos) & nrf.SAADC_CH_CONFIG_RESN_Msk) |
+		((nrf.SAADC_CH_CONFIG_GAIN_Gain1_5 << nrf.SAADC_CH_CONFIG_GAIN_Pos) & nrf.SAADC_CH_CONFIG_GAIN_Msk) |
+		((nrf.SAADC_CH_CONFIG_REFSEL_Internal << nrf.SAADC_CH_CONFIG_REFSEL_Pos) & nrf.SAADC_CH_CONFIG_REFSEL_Msk) |
+		((nrf.SAADC_CH_CONFIG_TACQ_3us << nrf.SAADC_CH_CONFIG_TACQ_Pos) & nrf.SAADC_CH_CONFIG_TACQ_Msk) |
+		((nrf.SAADC_CH_CONFIG_MODE_SE << nrf.SAADC_CH_CONFIG_MODE_Pos) & nrf.SAADC_CH_CONFIG_MODE_Msk))
+
+	// Set pin to read.
+	nrf.SAADC.CH[0].PSELN.Set(pwmPin)
+	nrf.SAADC.CH[0].PSELP.Set(pwmPin)
+
+	// Destination for sample result.
+	nrf.SAADC.RESULT.PTR.Set(uint32(uintptr(unsafe.Pointer(&value))))
+	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)
+
+	// Disable the ADC.
+	nrf.SAADC.ENABLE.Set(nrf.SAADC_ENABLE_ENABLE_Disabled << nrf.SAADC_ENABLE_ENABLE_Pos)
+
+	if value < 0 {
+		value = 0
+	}
+
+	// Return 16-bit result from 12-bit value.
+	return uint16(value << 4)
+}
+
+// SPI
+func (spi SPI) setPins(sck, sdo, sdi Pin) {
+	if sck == 0 {
+		sck = SPI0_SCK_PIN
+	}
+	if sdo == 0 {
+		sdo = SPI0_SDO_PIN
+	}
+	if sdi == 0 {
+		sdi = SPI0_SDI_PIN
+	}
+	spi.Bus.PSEL.SCK.Set(uint32(sck))
+	spi.Bus.PSEL.MOSI.Set(uint32(sdo))
+	spi.Bus.PSEL.MISO.Set(uint32(sdi))
+}
+
+// InitPWM initializes the registers needed for PWM.
+func InitPWM() {
+	return
+}
+
+// Configure configures a PWM pin for output.
+func (pwm PWM) Configure() {
+}
+
+// Set turns on the duty cycle for a PWM pin using the provided value.
+func (pwm PWM) Set(value uint16) {
+	for i := 0; i < len(pwmChannelPins); i++ {
+		if pwmChannelPins[i] == 0xFFFFFFFF || pwmChannelPins[i] == uint32(pwm.Pin) {
+			pwmChannelPins[i] = uint32(pwm.Pin)
+			pwmChannelSequence[i] = (value >> 2) | 0x8000 // set bit 15 to invert polarity
+
+			p := pwms[i]
+
+			p.PSEL.OUT[0].Set(uint32(pwm.Pin))
+			p.PSEL.OUT[1].Set(uint32(pwm.Pin))
+			p.PSEL.OUT[2].Set(uint32(pwm.Pin))
+			p.PSEL.OUT[3].Set(uint32(pwm.Pin))
+			p.ENABLE.Set(nrf.PWM_ENABLE_ENABLE_Enabled << nrf.PWM_ENABLE_ENABLE_Pos)
+			p.PRESCALER.Set(nrf.PWM_PRESCALER_PRESCALER_DIV_2)
+			p.MODE.Set(nrf.PWM_MODE_UPDOWN_Up)
+			p.COUNTERTOP.Set(16384) // frequency
+			p.LOOP.Set(0)
+			p.DECODER.Set((nrf.PWM_DECODER_LOAD_Common << nrf.PWM_DECODER_LOAD_Pos) | (nrf.PWM_DECODER_MODE_RefreshCount << nrf.PWM_DECODER_MODE_Pos))
+			p.SEQ[0].PTR.Set(uint32(uintptr(unsafe.Pointer(&pwmChannelSequence[i]))))
+			p.SEQ[0].CNT.Set(1)
+			p.SEQ[0].REFRESH.Set(1)
+			p.SEQ[0].ENDDELAY.Set(0)
+			p.TASKS_SEQSTART[0].Set(1)
+
+			break
+		}
+	}
+}