IMX6ULL ADC

llin — Thu, 13 Dec 2018 18:57:48 GMT

We are using GPIO1_IO3, GPIO1_IO8, and GPIO1_IO9 as 3 ADC input pins to measure DC voltage in the range of 1.6V-1.8V. The reference VREFH is DC 3.3V. I've measure on the board, these voltages are as expected.

We are seeing that ADC read in Linux (sys/bus/iio/devices/iio:devices/in_voltage0/1/2_raw) in the range of 4050-4095. For a 12 bit ADC, these are absolutely too high.

I've checked our device tree file. There seems nothing suspicious for now. There was a bug, a 3.3V applied on one ADC input. It was fixed.

I verified with memtools on the IOMUX reg configuration. They are all 0xB0.

I also tried to recalibrate ADC through memtools. When CFG.ATRIG = 0, set GC.CAL = 1. The CALF flag is 0. It sounds that calibration is good.

Here are the related parts in our device tree file.

regulators {

compatible = "simple-bus";

#address-cells = <1>;

#size-cells = <0>;

reg_vref_3v3: regulator@1 {

compatible = "regulator-fixed";

regulator-name = "vref-3v3";

regulator-min-microvolt = <3300000>;

regulator-max-microvolt = <3300000>;

};

…

&adc1 {

pinctrl-names = "default";

pinctrl-0 = <&pinctrl_adc1>;

vref-supply = <&reg_vref_3v3>;

num-channels = <3>;

status = "okay";

};

….

pinctrl_adc1: adc1grp {

fsl,pins = <

MX6UL_PAD_GPIO1_IO03__GPIO1_IO03 0xb0 /* ADC_SYS4V0_SENSE (IN) */

MX6UL_PAD_GPIO1_IO09__GPIO1_IO09 0xb0 /* ADC_GEN3V6_SENSE (IN)*/

MX6UL_PAD_GPIO1_IO08__GPIO1_IO08 0xb0 /* ADC_LDO3V3_SENSE (IN)*/

};

Re: IMX6ULL ADC

igorpadykov — Sat, 15 Dec 2018 05:38:26 GMT

Hi Lang

one can test adc using commands described in sect.4.1.2.3 Programming Interface

attached Linux Manual and Demo Images on

i.MX Software|NXP

Best regards
igor
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