refactor(src/machine/nrf52xxx/adc): make resolution configurable, pointer receiver, move init code

Signed-off-by: Paul Schroeder <[email protected]>

Author: milkpirate

src/machine/machine_nrf52xxx.go

@@ -49,19 +49,31 @@ func CPUFrequency() uint32 {
 
 // 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(config ADCConfig) {
 	// Enable ADC.
-	// The ADC does not consume a noticeable amount of current simply by being
-	// enabled.
+	// The ADC does not consume a noticeable amount of current by being enabled.
 	nrf.SAADC.ENABLE.Set(nrf.SAADC_ENABLE_ENABLE_Enabled << nrf.SAADC_ENABLE_ENABLE_Pos)
+}
 
-	// Use fixed resolution of 12 bits.
-	// TODO: is it useful for users to change this?
-	nrf.SAADC.RESOLUTION.Set(nrf.SAADC_RESOLUTION_VAL_12bit)
+// Configure configures an ADC pin to be able to read analog data.
+// Reference voltage can be 150, 300, 600, 1200, 1800, 2400, 3000(default), 3600 mV
+// Resolution can be 8, 10, 12(default), 14 bits
+// SampleTime will be ceiled to 3(default), 5, 10, 15, 20 or 40(max) µS respectively
+// Samples can be 1(default), 2, 4, 8, 16, 32, 64, 128, 256 samples
+func (a *ADC) Configure(config ADCConfig) {
+	var resolution uint32
+	switch config.Resolution {
+	case 8:
+		resolution = SAADC_RESOLUTION_VAL_8bit
+	case 10:
+		resolution = SAADC_RESOLUTION_VAL_10bit
+	case 12:
+		resolution = SAADC_RESOLUTION_VAL_12bit
+	case 14:
+		resolution = SAADC_RESOLUTION_VAL_14bit
+	default:
+		resolution = SAADC_RESOLUTION_VAL_12bit
+	}
+	nrf.SAADC.RESOLUTION.Set(resolution)
 
 	var configVal uint32 = nrf.SAADC_CH_CONFIG_RESP_Bypass<<nrf.SAADC_CH_CONFIG_RESP_Pos |
 		nrf.SAADC_CH_CONFIG_RESP_Bypass<<nrf.SAADC_CH_CONFIG_RESN_Pos |
@@ -86,7 +98,7 @@ func (a ADC) Configure(config ADCConfig) {
 	case 3600: // 3.6V
 		configVal |= nrf.SAADC_CH_CONFIG_GAIN_Gain1_6 << nrf.SAADC_CH_CONFIG_GAIN_Pos
 	default:
-		// TODO: return an error
+		// TODO: return an error, will that interfere with any interfaced if one will be?
 	}
 
 	// Source resistance, according to table 41 on page 676 of the nrf52832 datasheet.
@@ -138,7 +150,7 @@ func (a ADC) Configure(config ADCConfig) {
 }
 
 // Get returns the current value of a ADC pin in the range 0..0xffff.
-func (a ADC) Get() uint16 {
+func (a *ADC) Get() uint16 {
 	var pwmPin uint32
 	var rawValue volatile.Register16