From 06f231468da34a546a3f0c6c3cd1483e21b47994 Mon Sep 17 00:00:00 2001
From: ardnew <andrew@ardnew.com>
Date: Tue, 15 Dec 2020 17:31:13 -0600
Subject: [PATCH] accept configuration struct for ADC parameters (#1533)

---
 src/examples/adc/adc.go         |   2 +-
 src/machine/adc.go              |  12 +++
 src/machine/machine_atsamd21.go |  53 +++++++++++--
 src/machine/machine_atsamd51.go | 130 ++++++++++++++++++--------------
 src/machine/machine_avr.go      |   2 +-
 src/machine/machine_generic.go  |   2 +-
 src/machine/machine_nrf52.go    | 117 ++++++++++++++++++++++++++++
 src/machine/machine_nrf52840.go | 117 ++++++++++++++++++++++++++++
 8 files changed, 371 insertions(+), 64 deletions(-)
 create mode 100644 src/machine/adc.go

diff --git a/src/examples/adc/adc.go b/src/examples/adc/adc.go
index 9b4ddd27..de8a7f88 100644
--- a/src/examples/adc/adc.go
+++ b/src/examples/adc/adc.go
@@ -15,7 +15,7 @@ func main() {
 	led.Configure(machine.PinConfig{Mode: machine.PinOutput})
 
 	sensor := machine.ADC{machine.ADC2}
-	sensor.Configure()
+	sensor.Configure(machine.ADCConfig{})
 
 	for {
 		val := sensor.Get()
diff --git a/src/machine/adc.go b/src/machine/adc.go
new file mode 100644
index 00000000..739ca2ed
--- /dev/null
+++ b/src/machine/adc.go
@@ -0,0 +1,12 @@
+package machine
+
+// Hardware abstraction layer for the analog-to-digital conversion (ADC)
+// peripheral.
+
+// ADCConfig holds ADC configuration parameters. If left unspecified, the zero
+// value of each parameter will use the peripheral's default settings.
+type ADCConfig struct {
+	Reference  uint32 // analog reference voltage (AREF) in millivolts
+	Resolution uint32 // number of bits for a single conversion (e.g., 8, 10, 12)
+	Samples    uint32 // number of samples for a single conversion (e.g., 4, 8, 16, 32)
+}
diff --git a/src/machine/machine_atsamd21.go b/src/machine/machine_atsamd21.go
index b40db545..f93fcf68 100644
--- a/src/machine/machine_atsamd21.go
+++ b/src/machine/machine_atsamd21.go
@@ -307,13 +307,30 @@ func InitADC() {
 
 	// set calibration
 	sam.ADC.CALIB.Set((bias << 8) | linearity)
+}
+
+// Configure configures a ADC pin to be able to be used to read data.
+func (a ADC) Configure(config ADCConfig) {
 
 	// Wait for synchronization
 	waitADCSync()
 
+	var resolution uint32
+	switch config.Resolution {
+	case 8:
+		resolution = sam.ADC_CTRLB_RESSEL_8BIT
+	case 10:
+		resolution = sam.ADC_CTRLB_RESSEL_10BIT
+	case 12:
+		resolution = sam.ADC_CTRLB_RESSEL_12BIT
+	case 16:
+		resolution = sam.ADC_CTRLB_RESSEL_16BIT
+	default:
+		resolution = sam.ADC_CTRLB_RESSEL_12BIT
+	}
 	// Divide Clock by 32 with 12 bits resolution as default
 	sam.ADC.CTRLB.Set((sam.ADC_CTRLB_PRESCALER_DIV32 << sam.ADC_CTRLB_PRESCALER_Pos) |
-		(sam.ADC_CTRLB_RESSEL_12BIT << sam.ADC_CTRLB_RESSEL_Pos))
+		uint16(resolution<<sam.ADC_CTRLB_RESSEL_Pos))
 
 	// Sampling Time Length
 	sam.ADC.SAMPCTRL.Set(5)
@@ -325,18 +342,44 @@ func InitADC() {
 	sam.ADC.INPUTCTRL.Set(sam.ADC_INPUTCTRL_MUXNEG_GND << sam.ADC_INPUTCTRL_MUXNEG_Pos)
 
 	// Averaging (see datasheet table in AVGCTRL register description)
-	sam.ADC.AVGCTRL.Set((sam.ADC_AVGCTRL_SAMPLENUM_1 << sam.ADC_AVGCTRL_SAMPLENUM_Pos) |
+	var samples uint32
+	switch config.Resolution {
+	case 1:
+		samples = sam.ADC_AVGCTRL_SAMPLENUM_1
+	case 2:
+		samples = sam.ADC_AVGCTRL_SAMPLENUM_2
+	case 4:
+		samples = sam.ADC_AVGCTRL_SAMPLENUM_4
+	case 8:
+		samples = sam.ADC_AVGCTRL_SAMPLENUM_8
+	case 16:
+		samples = sam.ADC_AVGCTRL_SAMPLENUM_16
+	case 32:
+		samples = sam.ADC_AVGCTRL_SAMPLENUM_32
+	case 64:
+		samples = sam.ADC_AVGCTRL_SAMPLENUM_64
+	case 128:
+		samples = sam.ADC_AVGCTRL_SAMPLENUM_128
+	case 256:
+		samples = sam.ADC_AVGCTRL_SAMPLENUM_256
+	case 512:
+		samples = sam.ADC_AVGCTRL_SAMPLENUM_512
+	case 1024:
+		samples = sam.ADC_AVGCTRL_SAMPLENUM_1024
+	default:
+		samples = sam.ADC_AVGCTRL_SAMPLENUM_1
+	}
+	sam.ADC.AVGCTRL.Set(uint8(samples<<sam.ADC_AVGCTRL_SAMPLENUM_Pos) |
 		(0x0 << sam.ADC_AVGCTRL_ADJRES_Pos))
 
+	// TODO: use config.Reference to set AREF level
+
 	// Analog Reference is AREF pin (3.3v)
 	sam.ADC.INPUTCTRL.SetBits(sam.ADC_INPUTCTRL_GAIN_DIV2 << sam.ADC_INPUTCTRL_GAIN_Pos)
 
 	// 1/2 VDDANA = 0.5 * 3V3 = 1.65V
 	sam.ADC.REFCTRL.SetBits(sam.ADC_REFCTRL_REFSEL_INTVCC1 << sam.ADC_REFCTRL_REFSEL_Pos)
-}
 
-// Configure configures a ADCPin to be able to be used to read data.
-func (a ADC) Configure() {
 	a.Pin.Configure(PinConfig{Mode: PinAnalog})
 	return
 }
diff --git a/src/machine/machine_atsamd51.go b/src/machine/machine_atsamd51.go
index e2d5124a..4098bc5e 100644
--- a/src/machine/machine_atsamd51.go
+++ b/src/machine/machine_atsamd51.go
@@ -720,65 +720,83 @@ func InitADC() {
 
 	// calibrate ADC1
 	sam.ADC1.CALIB.Set(uint16((biascomp | biasr2r | biasref) >> 16))
-
-	sam.ADC0.CTRLA.SetBits(sam.ADC_CTRLA_PRESCALER_DIV32 << sam.ADC_CTRLA_PRESCALER_Pos)
-	// adcs[i]->CTRLB.bit.RESSEL = ADC_CTRLB_RESSEL_10BIT_Val;
-	sam.ADC0.CTRLB.SetBits(sam.ADC_CTRLB_RESSEL_12BIT << sam.ADC_CTRLB_RESSEL_Pos)
-
-	// wait for sync
-	for sam.ADC0.SYNCBUSY.HasBits(sam.ADC_SYNCBUSY_CTRLB) {
-	}
-
-	// sampling Time Length
-	sam.ADC0.SAMPCTRL.Set(5)
-
-	// wait for sync
-	for sam.ADC0.SYNCBUSY.HasBits(sam.ADC_SYNCBUSY_SAMPCTRL) {
-	}
-
-	// No Negative input (Internal Ground)
-	sam.ADC0.INPUTCTRL.Set(sam.ADC_INPUTCTRL_MUXNEG_GND << sam.ADC_INPUTCTRL_MUXNEG_Pos)
-
-	// wait for sync
-	for sam.ADC0.SYNCBUSY.HasBits(sam.ADC_SYNCBUSY_INPUTCTRL) {
-	}
-
-	// Averaging (see datasheet table in AVGCTRL register description)
-	// 1 sample only (no oversampling nor averaging), adjusting result by 0
-	sam.ADC0.AVGCTRL.Set(sam.ADC_AVGCTRL_SAMPLENUM_1 | (0 << sam.ADC_AVGCTRL_ADJRES_Pos))
-
-	// wait for sync
-	for sam.ADC0.SYNCBUSY.HasBits(sam.ADC_SYNCBUSY_AVGCTRL) {
-	}
-
-	// same for ADC1, as for ADC0
-	sam.ADC1.CTRLA.SetBits(sam.ADC_CTRLA_PRESCALER_DIV32 << sam.ADC_CTRLA_PRESCALER_Pos)
-	sam.ADC1.CTRLB.SetBits(sam.ADC_CTRLB_RESSEL_12BIT << sam.ADC_CTRLB_RESSEL_Pos)
-	for sam.ADC1.SYNCBUSY.HasBits(sam.ADC_SYNCBUSY_CTRLB) {
-	}
-	sam.ADC1.SAMPCTRL.Set(5)
-	for sam.ADC1.SYNCBUSY.HasBits(sam.ADC_SYNCBUSY_SAMPCTRL) {
-	}
-	sam.ADC1.INPUTCTRL.Set(sam.ADC_INPUTCTRL_MUXNEG_GND << sam.ADC_INPUTCTRL_MUXNEG_Pos)
-	for sam.ADC1.SYNCBUSY.HasBits(sam.ADC_SYNCBUSY_INPUTCTRL) {
-	}
-	sam.ADC1.AVGCTRL.Set(sam.ADC_AVGCTRL_SAMPLENUM_1 | (0 << sam.ADC_AVGCTRL_ADJRES_Pos))
-	for sam.ADC1.SYNCBUSY.HasBits(sam.ADC_SYNCBUSY_AVGCTRL) {
-	}
-
-	// wait for sync
-	for sam.ADC0.SYNCBUSY.HasBits(sam.ADC_SYNCBUSY_REFCTRL) {
-	}
-	for sam.ADC1.SYNCBUSY.HasBits(sam.ADC_SYNCBUSY_REFCTRL) {
-	}
-
-	// default is 3V3 reference voltage
-	sam.ADC0.REFCTRL.SetBits(sam.ADC_REFCTRL_REFSEL_INTVCC1)
-	sam.ADC1.REFCTRL.SetBits(sam.ADC_REFCTRL_REFSEL_INTVCC1)
 }
 
 // Configure configures a ADCPin to be able to be used to read data.
-func (a ADC) Configure() {
+func (a ADC) Configure(config ADCConfig) {
+
+	for _, adc := range []*sam.ADC_Type{sam.ADC0, sam.ADC1} {
+
+		for adc.SYNCBUSY.HasBits(sam.ADC_SYNCBUSY_CTRLB) {
+		} // wait for sync
+
+		adc.CTRLA.SetBits(sam.ADC_CTRLA_PRESCALER_DIV32 << sam.ADC_CTRLA_PRESCALER_Pos)
+		var resolution uint32
+		switch config.Resolution {
+		case 8:
+			resolution = sam.ADC_CTRLB_RESSEL_8BIT
+		case 10:
+			resolution = sam.ADC_CTRLB_RESSEL_10BIT
+		case 12:
+			resolution = sam.ADC_CTRLB_RESSEL_12BIT
+		case 16:
+			resolution = sam.ADC_CTRLB_RESSEL_16BIT
+		default:
+			resolution = sam.ADC_CTRLB_RESSEL_12BIT
+		}
+		adc.CTRLB.SetBits(uint16(resolution << sam.ADC_CTRLB_RESSEL_Pos))
+		adc.SAMPCTRL.Set(5) // sampling Time Length
+
+		for adc.SYNCBUSY.HasBits(sam.ADC_SYNCBUSY_SAMPCTRL) {
+		} // wait for sync
+
+		// No Negative input (Internal Ground)
+		adc.INPUTCTRL.Set(sam.ADC_INPUTCTRL_MUXNEG_GND << sam.ADC_INPUTCTRL_MUXNEG_Pos)
+		for adc.SYNCBUSY.HasBits(sam.ADC_SYNCBUSY_INPUTCTRL) {
+		} // wait for sync
+
+		// Averaging (see datasheet table in AVGCTRL register description)
+		var samples uint32
+		switch config.Resolution {
+		case 1:
+			samples = sam.ADC_AVGCTRL_SAMPLENUM_1
+		case 2:
+			samples = sam.ADC_AVGCTRL_SAMPLENUM_2
+		case 4:
+			samples = sam.ADC_AVGCTRL_SAMPLENUM_4
+		case 8:
+			samples = sam.ADC_AVGCTRL_SAMPLENUM_8
+		case 16:
+			samples = sam.ADC_AVGCTRL_SAMPLENUM_16
+		case 32:
+			samples = sam.ADC_AVGCTRL_SAMPLENUM_32
+		case 64:
+			samples = sam.ADC_AVGCTRL_SAMPLENUM_64
+		case 128:
+			samples = sam.ADC_AVGCTRL_SAMPLENUM_128
+		case 256:
+			samples = sam.ADC_AVGCTRL_SAMPLENUM_256
+		case 512:
+			samples = sam.ADC_AVGCTRL_SAMPLENUM_512
+		case 1024:
+			samples = sam.ADC_AVGCTRL_SAMPLENUM_1024
+		default: // 1 sample only (no oversampling nor averaging), adjusting result by 0
+			samples = sam.ADC_AVGCTRL_SAMPLENUM_1
+		}
+		adc.AVGCTRL.Set(uint8(samples<<sam.ADC_AVGCTRL_SAMPLENUM_Pos) |
+			(0 << sam.ADC_AVGCTRL_ADJRES_Pos))
+
+		for adc.SYNCBUSY.HasBits(sam.ADC_SYNCBUSY_AVGCTRL) {
+		} // wait for sync
+		for adc.SYNCBUSY.HasBits(sam.ADC_SYNCBUSY_REFCTRL) {
+		} // wait for sync
+
+		// TODO: use config.Reference to set AREF level
+
+		// default is 3V3 reference voltage
+		adc.REFCTRL.SetBits(sam.ADC_REFCTRL_REFSEL_INTVCC1)
+	}
+
 	a.Pin.Configure(PinConfig{Mode: PinAnalog})
 }
 
diff --git a/src/machine/machine_avr.go b/src/machine/machine_avr.go
index f1dbf89d..d7db15ae 100644
--- a/src/machine/machine_avr.go
+++ b/src/machine/machine_avr.go
@@ -118,7 +118,7 @@ func InitADC() {
 }
 
 // Configure configures a ADCPin to be able to be used to read data.
-func (a ADC) Configure() {
+func (a ADC) Configure(ADCConfig) {
 	return // no pin specific setup on AVR machine.
 }
 
diff --git a/src/machine/machine_generic.go b/src/machine/machine_generic.go
index 7e2d8ca3..65be3c96 100644
--- a/src/machine/machine_generic.go
+++ b/src/machine/machine_generic.go
@@ -73,7 +73,7 @@ func InitADC() {
 }
 
 // Configure configures an ADC pin to be able to be used to read data.
-func (adc ADC) Configure() {
+func (adc ADC) Configure(ADCConfig) {
 }
 
 // Get reads the current analog value from this ADC peripheral.
diff --git a/src/machine/machine_nrf52.go b/src/machine/machine_nrf52.go
index 189f0a32..82910d9e 100644
--- a/src/machine/machine_nrf52.go
+++ b/src/machine/machine_nrf52.go
@@ -4,6 +4,7 @@ package machine
 
 import (
 	"device/nrf"
+	"unsafe"
 )
 
 // Hardware pins
@@ -61,6 +62,122 @@ 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(ADCConfig) {
+	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}
diff --git a/src/machine/machine_nrf52840.go b/src/machine/machine_nrf52840.go
index 157495dc..78646937 100644
--- a/src/machine/machine_nrf52840.go
+++ b/src/machine/machine_nrf52840.go
@@ -4,6 +4,7 @@ package machine
 
 import (
 	"device/nrf"
+	"unsafe"
 )
 
 // Hardware pins
@@ -77,6 +78,122 @@ 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(ADCConfig) {
+	return // 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}