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[nrf fromlist] drivers: adc: nrfx: enable negative values for single-ended ADC readings #3147

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Merged
merged 1 commit into from
Aug 8, 2025
Merged

[nrf fromlist] drivers: adc: nrfx: enable negative values for single-ended ADC readings #3147

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20 changes: 14 additions & 6 deletions drivers/adc/adc_nrfx_saadc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -187,22 +187,24 @@

if (channel_cfg->differential) {
if (channel_cfg->input_negative > ARRAY_SIZE(saadc_psels) ||
channel_cfg->input_negative < NRF_SAADC_AIN0 ||
(IS_ENABLED(CONFIG_NRF_PLATFORM_HALTIUM) &&
(channel_cfg->input_positive > NRF_SAADC_AIN7) !=
(channel_cfg->input_negative > NRF_SAADC_AIN7))) {
LOG_ERR("Invalid analog negative input number: %d",
channel_cfg->input_negative);
return -EINVAL;
}
*pin_n = saadc_psels[channel_cfg->input_negative];
*pin_n = channel_cfg->input_negative == NRF_SAADC_GND ?
NRF_SAADC_INPUT_DISABLED :
saadc_psels[channel_cfg->input_negative];
} else {

Check notice on line 200 in drivers/adc/adc_nrfx_saadc.c

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drivers/adc/adc_nrfx_saadc.c:200 
-		*pin_n = channel_cfg->input_negative == NRF_SAADC_GND ?
-			 NRF_SAADC_INPUT_DISABLED :
-			 saadc_psels[channel_cfg->input_negative];
+		*pin_n = channel_cfg->input_negative == NRF_SAADC_GND
+				 ? NRF_SAADC_INPUT_DISABLED
+				 : saadc_psels[channel_cfg->input_negative];
*pin_n = NRF_SAADC_INPUT_DISABLED;
}
#else
*pin_p = channel_cfg->input_positive;
*pin_n = channel_cfg->differential ? channel_cfg->input_negative
: NRF_SAADC_INPUT_DISABLED;
*pin_n = (channel_cfg->differential && (channel_cfg->input_negative != NRF_SAADC_GND))
? channel_cfg->input_negative
: NRF_SAADC_INPUT_DISABLED;
#endif
LOG_DBG("ADC positive input: %d", *pin_p);
LOG_DBG("ADC negative input: %d", *pin_n);
Expand Down Expand Up @@ -352,8 +354,14 @@
* after ADC sequence ends.
*/
if (channel_cfg->differential) {
ch_cfg->mode = NRF_SAADC_MODE_DIFFERENTIAL;
m_data.single_ended_channels &= ~BIT(channel_cfg->channel_id);
if (channel_cfg->input_negative == NRF_SAADC_GND) {
ch_cfg->mode = NRF_SAADC_MODE_SINGLE_ENDED;
/* Do not mark as single-ended to not correct negative values. */
m_data.single_ended_channels &= ~BIT(channel_cfg->channel_id);
} else {
ch_cfg->mode = NRF_SAADC_MODE_DIFFERENTIAL;
m_data.single_ended_channels &= ~BIT(channel_cfg->channel_id);
}
} else {
ch_cfg->mode = NRF_SAADC_MODE_SINGLE_ENDED;
m_data.single_ended_channels |= BIT(channel_cfg->channel_id);
Expand Down
24 changes: 24 additions & 0 deletions include/zephyr/dt-bindings/adc/nrf-saadc.h
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,30 @@
#ifndef ZEPHYR_INCLUDE_DT_BINDINGS_ADC_NRF_SAADC_H_
#define ZEPHYR_INCLUDE_DT_BINDINGS_ADC_NRF_SAADC_H_

/**
* @brief Short ADC negative input to ground
*
* @details The nRF SAADC hardware only supports differential readings.
* The nRF SAADC SE (single ended) mode is differential with the negative
* input shorted to GND (ground). To use the nRF SAADC SE mode, set the
* negative input to NRF_SAADC_GND:
*
* @code{.dts}
* zephyr,input-positive = <NRF_SAADC_AIN3>;
* zephyr,input-negative = <NRF_SAADC_GND>;
* @endcode
*
* The nRF SAADC driver also supports using the nRF SAADC SE mode in
* emulated "single-ended" mode, as defined by zephyr. In this mode,
* negative readings will be clamped to 0 by software to emulate the
* behavior of an ADC in "single-ended" mode, as defined by zephyr. To
* do this, only define the positive input:
*
* @code{.dts}
* zephyr,input-positive = <NRF_SAADC_AIN3>;
* @endcode
*/
#define NRF_SAADC_GND 0
#define NRF_SAADC_AIN0 1
#define NRF_SAADC_AIN1 2
#define NRF_SAADC_AIN2 3
Expand Down
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