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cpu/sam0_common: adc: implement 16 bit mode by oversampling #19165

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Feb 24, 2023
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cpu/sam0_common: adc: implement 16 bit mode by oversampling #19165

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15 changes: 13 additions & 2 deletions cpu/sam0_common/include/periph_cpu_common.h
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Original file line number Diff line number Diff line change
Expand Up @@ -821,9 +821,20 @@ typedef enum {
ADC_RES_10BIT = ADC_CTRLC_RESSEL_10BIT_Val, /**< ADC resolution: 10 bit */
ADC_RES_12BIT = ADC_CTRLC_RESSEL_12BIT_Val, /**< ADC resolution: 12 bit */
#endif
ADC_RES_14BIT = 0xfe, /**< not supported */
ADC_RES_16BIT = 0xfd /**< not supported */
ADC_RES_16BIT_2SAMPL = ( 0x1 << 2) | 0x1, /**< sum of 2 12 bit samples */
ADC_RES_16BIT_4SAMPL = ( 0x2 << 2) | 0x1, /**< sum of 4 12 bit samples */
ADC_RES_16BIT_8SAMPL = ( 0x3 << 2) | 0x1, /**< sum of 8 12 bit samples */
ADC_RES_16BIT_16SAMPL = ( 0x4 << 2) | 0x1, /**< sum of 16 12 bit samples */
ADC_RES_16BIT_32SAMPL = ( 0x5 << 2) | 0x1, /**< sum of 32 12 bit samples */
ADC_RES_16BIT_64SAMPL = ( 0x6 << 2) | 0x1, /**< sum of 64 12 bit samples */
ADC_RES_16BIT_128SAMPL = ( 0x7 << 2) | 0x1, /**< sum of 128 12 bit samples */
ADC_RES_16BIT_256SAMPL = ( 0x8 << 2) | 0x1, /**< sum of 256 12 bit samples */
ADC_RES_16BIT_512SAMPL = ( 0x9 << 2) | 0x1, /**< sum of 512 12 bit samples */
ADC_RES_16BIT_1024SAMPL = ( 0xA << 2) | 0x1, /**< sum of 1024 12 bit samples */
ADC_RES_14BIT = 0xfe, /**< not supported */
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} adc_res_t;

#define ADC_RES_16BIT ADC_RES_16BIT_16SAMPL /**< default to 16x oversampling */
#endif /* DOXYGEN */

/**
Expand Down
30 changes: 21 additions & 9 deletions cpu/sam0_common/periph/adc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,7 @@
#include "periph/gpio.h"
#include "periph/adc.h"
#include "periph_conf.h"
#include "macros/utils.h"
#include "mutex.h"

#define ENABLE_DEBUG 0
Expand Down Expand Up @@ -181,11 +182,7 @@ static void _setup_calibration(Adc *dev)

static int _adc_configure(Adc *dev, adc_res_t res)
{
/* Individual comparison necessary because ADC Resolution Bits are not
* numerically in order and 16Bit (averaging - not currently supported)
* falls between 12bit and 10bit. See datasheet for details */
if (!((res == ADC_RES_8BIT) || (res == ADC_RES_10BIT) ||
(res == ADC_RES_12BIT))){
if ((res == ADC_RES_6BIT) || (res == ADC_RES_14BIT)) {
return -1;
}

Expand All @@ -203,10 +200,10 @@ static int _adc_configure(Adc *dev, adc_res_t res)
/* Set ADC resolution */
#ifdef ADC_CTRLC_RESSEL
/* Reset resolution bits in CTRLC */
dev->CTRLC.bit.RESSEL = res;
dev->CTRLC.bit.RESSEL = res & 0x3;
#else
/* Reset resolution bits in CTRLB */
dev->CTRLB.bit.RESSEL = res;
dev->CTRLB.bit.RESSEL = res & 0x3;
#endif

/* Set Voltage Reference */
Expand Down Expand Up @@ -241,6 +238,12 @@ static int _adc_configure(Adc *dev, adc_res_t res)
}
#endif

if ((res & 0x3) == 1) {
dev->AVGCTRL.reg = ADC_AVGCTRL_SAMPLENUM(res >> 2);
} else {
dev->AVGCTRL.reg = 0;
}

/* Enable ADC Module */
dev->CTRLA.reg |= ADC_CTRLA_ENABLE;
_wait_syncbusy(dev);
Expand Down Expand Up @@ -325,14 +328,23 @@ int32_t adc_sample(adc_t line, adc_res_t res)
/* Wait for the result */
while (!(dev->INTFLAG.reg & ADC_INTFLAG_RESRDY)) {}

int16_t result = dev->RESULT.reg;
uint16_t sample = dev->RESULT.reg;
int result;

_adc_poweroff(dev);
_done();

/* in differential mode we lose one bit for the sign */
if (diffmode) {
result *= 2;
result = 2 * (int16_t)sample;
} else {
result = sample;
}

/* 16 bit mode is implemented as oversampling */
if ((res & 0x3) == 1) {
/* ADC does automatic right shifts beyond 16 samples */
result <<= (4 - MIN(4, res >> 2));
}

return result;
Expand Down