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Linux/AM3352: How to read the value of analog line?

yingjie gu
Intellectual 810 points
Part Number: AM3352

Tool/software: Linux

Hi, 

I am using am3352 with linux 4.14.  I need to check the voltage on analog line, e.g. the voltage usb0 and some others. Is there a convenient way of getting the value by software?

Thanks.

  • 0
    TI__Guru**** 170625 points

    Hi Yingjie,

    Could you please provide more details regarding your request. Do you need to check a AM335x device pin voltage value by Software?

    Regards,
    Pavel

  • 0 in reply to Pavel Botev
    Intellectual 810 points

    Hi Pavel,

    I need to get the value of AIN0-AIN3 by software. The value on these pins is voltage from different source in our am3352 board. 

  • 0 in reply to yingjie gu
    TI__Guru** 101910 points

    Hello Yingjie,

    If you want to read voltage values on the ADC input pins, take a look at our Kernel driver ADC documentation.

    Regards,

    Nick

  • 0 in reply to Nick Saulnier
    TI__Guru** 101910 points

    One note: please make sure that the input voltage to the ADC pins is always 1.8V or lower. If you try connecting a higher voltage to the ADC input pins, then you could damage your processor. Do NOT connect a 5V USB signal directly to your ADC pins, because you will damage your part.

    Regards,

    Nick

  • 0 in reply to Nick Saulnier
    Intellectual 810 points

    Hi Nick,

    I enabled ADC driver in config file and edited dts as suggested. 

    After the system boot up, all in_voltagex_raw is 4095, and scan_elements/in_voltagex_en are all 0. 

    The CONFIG is as following:

    CONFIG_MFD_TI_AM335X_TSCADC=m

    CONFIG_IIO=m

    CONFIG_IIO_BUFFER=y

    CONFIG_IIO_KFIFO_BUF=m

    CONFIG_TI_AM335X_ADC=m


    The dts files are as following:

    In am33xx.dtsi:

                    tscadc: tscadc@44e0d000 {

                            compatible = "ti,am3359-tscadc";

                            reg = <0x44e0d000 0x1000>;

                            interrupts = <16>;

                            ti,hwmods = "adc_tsc";

                            status = "disabled";

                            dmas = <&edma 53 0>, <&edma 57 0>;

                            dma-names = "fifo0", "fifo1";

                            am335x_adc: adc {

                                    #io-channel-cells = <8>;

                                    compatible = "ti,am3359-adc";

                            };

                    };

    In am335x-myboard.dts :


    &tscadc {

    status = "okay";

    adc {

    ti,adc-channels = <0 1 2 3 4 5 6 7>;

    };

    };

    How can I enable these pins? 

    Thanks. 



  • 0 in reply to yingjie gu
    TI__Guru** 101910 points

    Hello Yingjie,

    Please clarify on what you mean by "How can I enable these pins?".

    As per our ADC Linux driver documentation, I would expect that cat /sys/bus/iio/devices/iio\:device0/in_voltageX_raw should give 4095 if you have 1.8V connected to the pins, and a lower value if you have a lower voltage connected to the pins.

    Take a look at the "How to set it up" section of the ADC documentation for guidance on how to set in_voltageX_en when you are reading ADC data continuously.

    Regards,

    Nick

  • 0 in reply to Nick Saulnier
    Intellectual 810 points

    Thanks Nick,

    The resistors on board are wrong. After changing it, now I got correct value.