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nrf: add sample time to ADC

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This is important for inputs with a high input resistance. In those
cases, the sample time needs to be longer.
This commit is contained in:
Ayke van Laethem
2023-05-09 16:22:13 +02:00
committed by Ron Evans
parent e82f595f37
commit 868812717f
2 changed files with 17 additions and 1 deletions
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src/machine/adc.go
+1
View File
@@ -9,4 +9,5 @@ type ADCConfig struct {
Reference uint32 // analog reference voltage (AREF) in millivolts
Resolution uint32 // number of bits for a single conversion (e.g., 8, 10, 12)
Samples uint32 // number of samples for a single conversion (e.g., 4, 8, 16, 32)
SampleTime uint32 // sample time, in microseconds (µs)
}
src/machine/machine_nrf52xxx.go
+16 -1
View File
@@ -30,7 +30,6 @@ 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_REFSEL_Internal<<nrf.SAADC_CH_CONFIG_REFSEL_Pos |
nrf.SAADC_CH_CONFIG_TACQ_3us<<nrf.SAADC_CH_CONFIG_TACQ_Pos |
nrf.SAADC_CH_CONFIG_MODE_SE<<nrf.SAADC_CH_CONFIG_MODE_Pos
switch config.Reference {
@@ -54,6 +53,22 @@ func (a ADC) Configure(config ADCConfig) {
// TODO: return an error
}
// Source resistance, according to table 89 on page 364 of the nrf52832 datasheet.
// https://infocenter.nordicsemi.com/pdf/nRF52832_PS_v1.4.pdf
if config.SampleTime <= 3 { // <= 10kΩ
configVal |= nrf.SAADC_CH_CONFIG_TACQ_3us << nrf.SAADC_CH_CONFIG_TACQ_Pos
} else if config.SampleTime <= 5 { // <= 40kΩ
configVal |= nrf.SAADC_CH_CONFIG_TACQ_5us << nrf.SAADC_CH_CONFIG_TACQ_Pos
} else if config.SampleTime <= 10 { // <= 100kΩ
configVal |= nrf.SAADC_CH_CONFIG_TACQ_10us << nrf.SAADC_CH_CONFIG_TACQ_Pos
} else if config.SampleTime <= 15 { // <= 200kΩ
configVal |= nrf.SAADC_CH_CONFIG_TACQ_15us << nrf.SAADC_CH_CONFIG_TACQ_Pos
} else if config.SampleTime <= 20 { // <= 400kΩ
configVal |= nrf.SAADC_CH_CONFIG_TACQ_20us << nrf.SAADC_CH_CONFIG_TACQ_Pos
} else { // <= 800kΩ
configVal |= nrf.SAADC_CH_CONFIG_TACQ_40us << nrf.SAADC_CH_CONFIG_TACQ_Pos
}
// Configure channel 0, which is the only channel we use.
nrf.SAADC.CH[0].CONFIG.Set(configVal)
}