ADC data abnormal in some channel for LPC55s69

[MarsMSWu]

Hi, all
I have some question for the ADC channel.
Currently, I use ADC define in dts file as below :

zephyr,user {
    io-channels = <&adc0 0 &adc0 1 &adc0 2 &adc0 3 &adc0 4 &adc0 8 &adc0 11 &adc0 12>;
};

channel@0 {
	reg = <0>;
	zephyr,gain = "ADC_GAIN_1";
	zephyr,reference = "ADC_REF_EXTERNAL0";
	zephyr,vref-mv = <3300>;
	zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
	zephyr,resolution = <16>;
	zephyr,input-positive = <MCUX_LPADC_CH0A>;
};

channel@1 {
	reg = <1>;
	zephyr,gain = "ADC_GAIN_1";
	zephyr,reference = "ADC_REF_EXTERNAL0";
	zephyr,vref-mv = <3300>;
	zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
	zephyr,resolution = <16>;
	zephyr,input-positive = <MCUX_LPADC_CH1A>;
};

channel@2 {
	reg = <2>;
	zephyr,gain = "ADC_GAIN_1";
	zephyr,reference = "ADC_REF_EXTERNAL0";
	zephyr,vref-mv = <3300>;
	zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
	zephyr,resolution = <16>;
	zephyr,input-positive = <MCUX_LPADC_CH2A>;
};

channel@3 {
	reg = <3>;
	zephyr,gain = "ADC_GAIN_1";
	zephyr,reference = "ADC_REF_EXTERNAL0";
	zephyr,vref-mv = <3300>;
	zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
	zephyr,resolution = <16>;
	zephyr,input-positive = <MCUX_LPADC_CH3A>;
};

channel@4 {
    reg = <4>;
    zephyr,gain = "ADC_GAIN_1";
    zephyr,reference = "ADC_REF_EXTERNAL0";
    zephyr,vref-mv = <3300>;
    zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
    zephyr,resolution = <16>;
    zephyr,input-positive = <MCUX_LPADC_CH4A>;
};

channel@8 {
	reg = <8>;
	zephyr,gain = "ADC_GAIN_1";
	zephyr,reference = "ADC_REF_EXTERNAL0";
	zephyr,vref-mv = <3300>;
	zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
	zephyr,resolution = <16>;
	zephyr,input-positive = <MCUX_LPADC_CH0B>;
};

channel@11 {
	reg = <11>;
	zephyr,gain = "ADC_GAIN_1";
	zephyr,reference = "ADC_REF_EXTERNAL0";
	zephyr,vref-mv = <3300>;
	zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
	zephyr,resolution = <16>;
	zephyr,input-positive = <MCUX_LPADC_CH3B>;
};

channel@12 {
	reg = <12>;
	zephyr,gain = "ADC_GAIN_1";
	zephyr,reference = "ADC_REF_EXTERNAL0";
	zephyr,vref-mv = <3300>;
	zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
	zephyr,resolution = <16>;
	zephyr,input-positive = <MCUX_LPADC_CH4B>;
};

pinmux_adc0_default: pinmux_adc0_default {
	group0 {
		pinmux = <ADC0_CH0_PIO0_23>,
			<ADC0_CH1_PIO0_10>,
			<ADC0_CH2_PIO0_15>,
			<ADC0_CH3_PIO0_31>,
			<ADC0_CH4_PIO1_8>,
			<ADC0_CH8_PIO0_16>,
			<ADC0_CH11_PIO1_0>,
			<ADC0_CH12_PIO1_9>;
		slew-rate = "standard";
		nxp,analog-mode;
	};
};

In my real test, only ADC0_12, ADC0_8 and ADC0_1 can get positive result.
These three channel use default external pull-high 3.3V and can get digital value 65xxx in my console log.
If I force GND these three channel and can get 0~10 value.
So I think at least these three channel configuration should be correct.
I add other ADC channels and set related channel and side, other setting are the same but result is not reach my expect.
I don't know is need any extra configure or maybe limitation...

Thanks.

[DerekSnell]

Hi @MarsMSWu ,
Your devicetree looks fine to me. In fact, I used your devicetree as the attached
lpcxpresso55s69_cpu0.overlay, and I tested on the LPCXpresso55S69 board. Each ADC channel measured as expected for me. To test, I used the overlay with the ADC driver sample.

Can you try that sample and see how it compares for you? Let us know what you find.

The console output:

*** Booting Zephyr OS build zephyr-v3.5.0-4933-g70809cc429cc ***                
ADC reading[0]:                                                                 
- adc@A0000, channel 0: 24837 = 1250 mV                                         
- adc@A0000, channel 1: 57933 = 2917 mV                                         
- adc@A0000, channel 2: 37633 = 1894 mV                                         
- adc@A0000, channel 3: 53145 = 2676 mV                                         
- adc@A0000, channel 4: 38342 = 1930 mV                                         
- adc@A0000, channel 8: 35203 = 1772 mV                                         
- adc@A0000, channel 11: 55485 = 2793 mV                                        
- adc@A0000, channel 12: 56591 = 2849 mV   

[MarsMSWu]

Hi @DerekSnell ,

It 's very thanks for your feedback.
I think maybe is wrong data type then also get a incorrect result.

We use a integer type to get the data and put to unsigned integer type and conversion to mV.
I don't know why buf data is negative...then if assign to unsigned integer type will get a huge and incorrect result.

If we use unsigned integer data type for buf then can get correcr result.

Because that channel is using external pull-hi 3.3V so print the value in console is 65xxx, it meet our expected in early study.
The value 65xxx show on console should be mV data type which conversion by API function "adc_raw_to_millivolts_dt".

Thanks.