machine/nrf51: add ADC implementation

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

src/machine/machine_nrf51.go

@@ -187,3 +187,85 @@ func (spi SPI) Tx(w, r []byte) error {
 
 	return nil
 }
+
+// InitADC initializes the registers needed for ADC.
+func InitADC() {
+	return // no specific setup on nrf51 machine.
+}
+
+// Configure configures an ADC pin to be able to read analog data.
+func (a ADC) Configure(ADCConfig) {
+	return // no pin specific setup on nrf51 machine.
+}
+
+// Get returns the current value of a ADC pin in the range 0..0xffff.
+func (a ADC) Get() uint16 {
+	var value uint32
+
+	adcPin := a.getADCPin()
+
+	// Enable ADC.
+	nrf.ADC.SetENABLE(nrf.ADC_ENABLE_ENABLE_Enabled)
+
+	// Set pin to read.
+	nrf.ADC.SetCONFIG_PSEL(adcPin)
+
+	// config ADC
+	nrf.ADC.SetCONFIG_RES(nrf.ADC_CONFIG_RES_10bit)
+	nrf.ADC.SetCONFIG_INPSEL(nrf.ADC_CONFIG_INPSEL_AnalogInputOneThirdPrescaling)
+	nrf.ADC.SetCONFIG_REFSEL(nrf.ADC_CONFIG_REFSEL_SupplyOneThirdPrescaling)
+
+	// Start tasks.
+	nrf.ADC.TASKS_START.Set(1)
+
+	// Wait until the sample task is done.
+	for nrf.ADC.EVENTS_END.Get() == 0 {
+	}
+	nrf.ADC.EVENTS_END.Set(0x00)
+
+	value = nrf.ADC.GetRESULT()
+
+	// Stop the ADC
+	nrf.ADC.TASKS_STOP.Set(1)
+
+	// Disable ADC.
+	nrf.ADC.SetENABLE(nrf.ADC_ENABLE_ENABLE_Disabled)
+
+	if value < 0 {
+		value = 0
+	}
+
+	// Return 16-bit result from 10-bit value.
+	return uint16(value << 6)
+}
+
+func (a ADC) getADCPin() uint32 {
+	switch a.Pin {
+	case 1:
+		return nrf.ADC_CONFIG_PSEL_AnalogInput2
+
+	case 2:
+		return nrf.ADC_CONFIG_PSEL_AnalogInput3
+
+	case 3:
+		return nrf.ADC_CONFIG_PSEL_AnalogInput4
+
+	case 4:
+		return nrf.ADC_CONFIG_PSEL_AnalogInput5
+
+	case 5:
+		return nrf.ADC_CONFIG_PSEL_AnalogInput6
+
+	case 6:
+		return nrf.ADC_CONFIG_PSEL_AnalogInput7
+
+	case 26:
+		return nrf.ADC_CONFIG_PSEL_AnalogInput0
+
+	case 27:
+		return nrf.ADC_CONFIG_PSEL_AnalogInput1
+
+	default:
+		return 0
+	}
+}