nrf52: implement ADC and PWM interfaces

Signed-off-by: Ron Evans <ron@hybridgroup.com>

src/machine/board_pca10040.go

@@ -25,3 +25,13 @@ const (
 	UART_TX_PIN = 6
 	UART_RX_PIN = 8
 )
+
+// ADC pins
+const (
+	ADC0 = 3
+	ADC1 = 4
+	ADC2 = 28
+	ADC3 = 29
+	ADC4 = 30
+	ADC5 = 31
+)

src/machine/machine_nrf52.go

@@ -0,0 +1,154 @@
+// +build nrf52
+
+package machine
+
+import (
+	"device/nrf"
+	"unsafe"
+)
+
+// 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 = nrf.SAADC_RESOLUTION_VAL_12bit
+
+	// Enable ADC.
+	nrf.SAADC.ENABLE = (nrf.SAADC_ENABLE_ENABLE_Enabled << nrf.SAADC_ENABLE_ENABLE_Pos)
+	for i := 0; i < 8; i++ {
+		nrf.SAADC.CH[i].PSELN = nrf.SAADC_CH_PSELP_PSELP_NC
+		nrf.SAADC.CH[i].PSELP = nrf.SAADC_CH_PSELP_PSELP_NC
+	}
+
+	// Configure ADC.
+	nrf.SAADC.CH[0].CONFIG = ((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 = nrf.RegValue(pwmPin)
+	nrf.SAADC.CH[0].PSELP = nrf.RegValue(pwmPin)
+
+	// Destination for sample result.
+	nrf.SAADC.RESULT.PTR = nrf.RegValue(uintptr(unsafe.Pointer(&value)))
+	nrf.SAADC.RESULT.MAXCNT = 1 // One sample
+
+	// Start tasks.
+	nrf.SAADC.TASKS_START = 1
+	for nrf.SAADC.EVENTS_STARTED == 0 {
+	}
+	nrf.SAADC.EVENTS_STARTED = 0x00
+
+	// Start the sample task.
+	nrf.SAADC.TASKS_SAMPLE = 1
+
+	// Wait until the sample task is done.
+	for nrf.SAADC.EVENTS_END == 0 {
+	}
+	nrf.SAADC.EVENTS_END = 0x00
+
+	// Stop the ADC
+	nrf.SAADC.TASKS_STOP = 1
+	for nrf.SAADC.EVENTS_STOPPED == 0 {
+	}
+	nrf.SAADC.EVENTS_STOPPED = 0
+
+	// Disable the ADC.
+	nrf.SAADC.ENABLE = (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() {
+}
+
+// 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] = nrf.RegValue(pwm.Pin)
+			p.PSEL.OUT[1] = nrf.RegValue(pwm.Pin)
+			p.PSEL.OUT[2] = nrf.RegValue(pwm.Pin)
+			p.PSEL.OUT[3] = nrf.RegValue(pwm.Pin)
+			p.ENABLE = (nrf.PWM_ENABLE_ENABLE_Enabled << nrf.PWM_ENABLE_ENABLE_Pos)
+			p.PRESCALER = nrf.PWM_PRESCALER_PRESCALER_DIV_2
+			p.MODE = nrf.PWM_MODE_UPDOWN_Up
+			p.COUNTERTOP = 16384 // frequency
+			p.LOOP = 0
+			p.DECODER = (nrf.PWM_DECODER_LOAD_Common << nrf.PWM_DECODER_LOAD_Pos) | (nrf.PWM_DECODER_MODE_RefreshCount << nrf.PWM_DECODER_MODE_Pos)
+			p.SEQ[0].PTR = nrf.RegValue(uintptr(unsafe.Pointer(&pwmChannelSequence[i])))
+			p.SEQ[0].CNT = 1
+			p.SEQ[0].REFRESH = 1
+			p.SEQ[0].ENDDELAY = 0
+			p.TASKS_SEQSTART[0] = 1
+
+			break
+		}
+	}
+}