machine/nrf51: add ADC implementation

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

Author: deadprogram

src/machine/machine_nrf51.go

@@ -187,3 +187,88 @@ 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)
+for nrf.ADC.EVENTS_END.Get() == 0 {
+}
+nrf.ADC.EVENTS_END.Set(0)
+
+// 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
+}
+}