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nrf: add support for reading VDDH on the nrf52840 #5103

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Merged
deadprogram merged 4 commits into from
Dec 4, 2025
Merged

nrf: add support for reading VDDH on the nrf52840 #5103

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56da26b
nrf: fix typo in ADC configuration
aykevl Nov 30, 2025
8294afc
nrf: don't set PSELN, it's ignored in single ended mode anyway
aykevl Nov 30, 2025
26c7023
nrf: rename pwmPin to adcPin
aykevl Nov 30, 2025
ee828b5
nrf: add ADC_VDDH which is an ADC pin for VDDH
aykevl Nov 30, 2025
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4 changes: 4 additions & 0 deletions src/machine/machine_nrf52840.go
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Original file line number Diff line number Diff line change
Expand Up @@ -110,3 +110,7 @@ func eraseBlockSize() int64 {
}

const spiMaxBufferSize = 0xffff // from the datasheet: TXD.MAXCNT and RXD.MAXCNT

// ADC instance for the VDDH input pin. This pin is typically connected to USB
// input voltage (~5V) or directly to a battery.
var ADC_VDDH = ADC{adcVDDHPin}
31 changes: 19 additions & 12 deletions src/machine/machine_nrf52xxx.go
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,8 @@ func CPUFrequency() uint32 {
return 64000000
}

var adcVDDHPin = Pin(254) // special pin number for VDDH on the nrf52840

// InitADC initializes the registers needed for ADC.
func InitADC() {
// Enable ADC.
Expand All @@ -26,7 +28,7 @@ func InitADC() {
// Samples can be 1(default), 2, 4, 8, 16, 32, 64, 128, 256 samples
func (a *ADC) Configure(config ADCConfig) {
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 |
nrf.SAADC_CH_CONFIG_RESN_Bypass<<nrf.SAADC_CH_CONFIG_RESN_Pos |
nrf.SAADC_CH_CONFIG_REFSEL_Internal<<nrf.SAADC_CH_CONFIG_REFSEL_Pos |
nrf.SAADC_CH_CONFIG_MODE_SE<<nrf.SAADC_CH_CONFIG_MODE_Pos

Expand Down Expand Up @@ -116,33 +118,38 @@ func (a *ADC) Configure(config ADCConfig) {

// Get returns the current value of an ADC pin in the range 0..0xffff.
func (a *ADC) Get() uint16 {
var pwmPin uint32
var adcPin uint32
var rawValue volatile.Register16

switch a.Pin {
case 2:
pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput0
adcPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput0
case 3:
pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput1
adcPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput1
case 4:
pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput2
adcPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput2
case 5:
pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput3
adcPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput3
case 28:
pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput4
adcPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput4
case 29:
pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput5
adcPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput5
case 30:
pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput6
adcPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput6
case 31:
pwmPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput7
adcPin = nrf.SAADC_CH_PSELP_PSELP_AnalogInput7
case adcVDDHPin:
if Device == "nrf52840" {
adcPin = 0x0D // VDDHDIV5 on the nrf52840
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@deadprogram deadprogram Dec 1, 2025

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Wouldn't it be better to define a constant here? Just a nit.

} else {
return 0
}
default:
return 0
}

// Set pin to read.
nrf.SAADC.CH[0].PSELN.Set(pwmPin)
nrf.SAADC.CH[0].PSELP.Set(pwmPin)
nrf.SAADC.CH[0].PSELP.Set(adcPin)

// Destination for sample result.
// Note: rawValue doesn't need to be kept alive for the GC, since the
Expand Down
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