iio: adc: ti_am335x_tscadc: Improve accuracy of measurement (4b3ab937) · Commits · 戴 / test

When performing single ended measurements with TSCADC, its recommended to set negative input (SEL_INM_SWC_3_0) of ADC step to ADC's VREFN in the corresponding STEP_CONFIGx register. Also, the positive(SEL_RFP_SWC_2_0) and negative(SEL_RFM_SWC_1_0) reference voltage for ADC step needs to be set to VREFP and VREFN respectively in STEP_CONFIGx register. Without these changes, there may be variation of as much as ~2% in the ADC's digital output which is bad for precise measurement. Signed-off-by:

Vignesh R <vigneshr@ti.com> Acked-by:

Jonathan Cameron <Jonathan.Cameron@huawei.com> Signed-off-by:

Lee Jones <lee.jones@linaro.org>

drivers/iio/adc/ti_am335x_adc.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -142,7 +142,10 @@ static void tiadc_step_config(struct iio_dev *indio_dev)
		stepconfig \|= STEPCONFIG_MODE_SWCNT;

		tiadc_writel(adc_dev, REG_STEPCONFIG(steps),
		stepconfig \| STEPCONFIG_INP(chan));
		stepconfig \| STEPCONFIG_INP(chan) \|
		STEPCONFIG_INM_ADCREFM \|
		STEPCONFIG_RFP_VREFP \|
		STEPCONFIG_RFM_VREFN);

		if (adc_dev->open_delay[i] > STEPDELAY_OPEN_MASK) {
		dev_warn(dev, "chan %d open delay truncating to 0x3FFFF\n",

include/linux/mfd/ti_am335x_tscadc.h

+4 −0

Original line number	Diff line number	Diff line
		@@ -78,6 +78,8 @@
		#define STEPCONFIG_YNN BIT(8)
		#define STEPCONFIG_XNP BIT(9)
		#define STEPCONFIG_YPN BIT(10)
		#define STEPCONFIG_RFP(val) ((val) << 12)
		#define STEPCONFIG_RFP_VREFP (0x3 << 12)
		#define STEPCONFIG_INM_MASK (0xF << 15)
		#define STEPCONFIG_INM(val) ((val) << 15)
		#define STEPCONFIG_INM_ADCREFM STEPCONFIG_INM(8)
		@@ -86,6 +88,8 @@
		#define STEPCONFIG_INP_AN4 STEPCONFIG_INP(4)
		#define STEPCONFIG_INP_ADCREFM STEPCONFIG_INP(8)
		#define STEPCONFIG_FIFO1 BIT(26)
		#define STEPCONFIG_RFM(val) ((val) << 23)
		#define STEPCONFIG_RFM_VREFN (0x3 << 23)

		/* Delay register */
		#define STEPDELAY_OPEN_MASK (0x3FFFF << 0)

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