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ADS7950: I/O Error with ADS7950 Configuration on iMX93

Daniel Samraj
Prodigy 10 points
Part Number: ADS7950

Tool/software:

Hi,

I am working with the following setup:

CPU: iMX93
IC: ADS7950
SPI: LPSPI7 chip select on GPIO2 4
OS: Yocto Linux based on kernel version L6.1.22

I'm getting I/O error while trying to read ADC channel values in sysfs.

Below is the relevant device tree configuration:

lpspi7: spi@42710000 {
#address-cells = <1>;
#size-cells = <0>;
compatible = "fsl,imx93-spi", "fsl,imx7ulp-spi";
reg = <0x42710000 0x10000>;
interrupts = <GIC_SPI 193 IRQ_TYPE_LEVEL_HIGH>;
clocks = <&clk IMX93_CLK_LPSPI7_GATE>,
<&clk IMX93_CLK_BUS_WAKEUP>;
clock-names = "per", "ipg";
};

&lpspi7 {
fsl,spi-num-chipselects = <1>;
pinctrl-names = "default", "sleep";
pinctrl-0 = <&pinctrl_lpspi7>, <&pinctrl_lpspi7_cs>;
pinctrl-1 = <&pinctrl_lpspi7>, <&pinctrl_lpspi7_cs>;
cs-gpios = <&gpio2 4 GPIO_ACTIVE_LOW>;
dmas = <&edma2 83 0 0>, <&edma2 84 0 1>;
dma-names = "tx","rx";
assigned-clock-rates = <30000000>;
status = "okay";

adc@0 {
compatible = "ti,ads7950";
reg = <0>; /* SPI chip select 0 */
vref-supply = <&reg_5v>;
spi-max-frequency = <10000000>;
#io-channel-cells = <1>;
status = "okay";

};
};

pinctrl_lpspi7: lpspi7grp { /* LPSPI7: LPSPI7 IOMUX Pin Configuration */
fsl,pins = <
MX93_PAD_GPIO_IO07__LPSPI7_SCK 0x3fe
MX93_PAD_GPIO_IO06__LPSPI7_SOUT 0x3fe
MX93_PAD_GPIO_IO05__LPSPI7_SIN 0x3fe
>;
};

pinctrl_lpspi7_cs: lpspi7_cs_grp {
fsl,pins = <
MX93_PAD_GPIO_IO04__GPIO2_IO04 0x31e
>;
};


To debug the issue, I added logging in the TI ADS7950 driver code as follows:

Driver code:

diff --git a/drivers/iio/adc/ti-ads7950.c b/drivers/iio/adc/ti-ads7950.c
index 2cc9a9bd9db6..d4ce4917d1fb 100644
--- a/drivers/iio/adc/ti-ads7950.c
+++ b/drivers/iio/adc/ti-ads7950.c
@@ -377,6 +377,8 @@ static int ti_ads7950_read_raw(struct iio_dev *indio_dev,
if (ret < 0)
return ret;

+ printk("Address: %u\n", (unsigned int)chan->address);
+ printk("Extracted Value: %u\n", (unsigned int)TI_ADS7950_EXTRACT(ret, 12, 4));
if (chan->address != TI_ADS7950_EXTRACT(ret, 12, 4))
return -EIO;

Error:

root@imx93-iwg50m-sodimm:~# cat /sys/bus/iio/devices/iio\:device1/in_voltage0_raw
[ 100.929228] Address: 0
[ 100.931641] Extracted Value: 15
cat: '/sys/bus/iio/devices/iio:device1/in_voltage0_raw': Input/output error
root@imx93-iwg50m-sodimm:~# cat /sys/bus/iio/devices/iio\:device1/in_voltage1_raw
[ 103.849178] Address: 1
[ 103.851563] Extracted Value: 15
cat: '/sys/bus/iio/devices/iio:device1/in_voltage1_raw': Input/output error
root@imx93-iwg50m-sodimm:~# cat /sys/bus/iio/devices/iio\:device1/in_voltage2_raw
[ 106.253289] Address: 2
[ 106.255694] Extracted Value: 15
cat: '/sys/bus/iio/devices/iio:device1/in_voltage2_raw': Input/output error
root@imx93-iwg50m-sodimm:~# cat /sys/bus/iio/devices/iio\:device1/in_voltage3_raw
[ 108.949172] Address: 3
[ 108.951597] Extracted Value: 15
cat: '/sys/bus/iio/devices/iio:device1/in_voltage3_raw': Input/output error
root@imx93-iwg50m-sodimm:~#

Could you please advise what might be causing this behavior or if there are any potential issues in my configuration or setup?

Regards,
Daniel

  • 0
    TI__Genius 14520 points

    Hi Daniel,

    It looks like you are trying to use the driver included in the Linux kernel for the ADS7950. Unfortunately, since this was not developed directly by TI, we can't support any questions in regard to that. I suggest you reach out to the developer of the code. 

    Otherwise, if you have a logic analyzer that you can hook up to the SPI pins, you can send a logic capture file over and I can attempt to debug what is going wrong in the communications.

    Regards,
    Joel

  • 0 in reply to Joel Meraz
    Prodigy 10 points

    Hi Joel,

    I’ve attached the logic capture file for your review. Please let me know your thoughts.

    ADS7950SBRGER-SPI7 (Logic output).sal

    Regards,
    Daniel


  • 0 in reply to Daniel Samraj
    TI__Genius 14520 points

    Hi Daniel,

    On my initial look, I'm seeing that ~CS falls while SCLK is high when transmission starts. This device has the option of having a continuous clock supplied (denoted by the dotted lines on SCLK in the timing diagram), but ~CS still needs to fall during the time that SCLK is low. The MCU should be configured to for SPI Mode 0 (CPOL = 0, CPHA = 0).

    Below is the capture of the condition that could be problematic for the device.

    And below shows how SCLK should be low before ~CS falls (CPOL= 1). 

    Once this is done, I can take a look to see if more issues are occurring.

    Regards,
    Joel

  • 0 in reply to Joel Meraz
    Prodigy 10 points

    Dear Joel,

    After changing the PAD CTL values of the pins , we were able to get the CS to go low when clock is low (Refer the attached logic analyzer image).



    These were the DTS changes.

    pinctrl_lpspi7: lpspi7grp { /* LPSPI7: LPSPI7 IOMUX Pin Configuration */
    fsl,pins = <
    MX93_PAD_GPIO_IO07__LPSPI7_SCK 0x141e
    MX93_PAD_GPIO_IO06__LPSPI7_SOUT 0x141e
    MX93_PAD_GPIO_IO05__LPSPI7_SIN 0x141e
    >;
    };

    pinctrl_lpspi7_cs: lpspi7_cs_grp {
    fsl,pins = <
    MX93_PAD_GPIO_IO04__GPIO2_IO04 0x402
    >;
    };


    But still we are getting IO errors on 3 channels and value 0 on channel 0. The value in channel 0 is not changing after giving external voltage.

    root@imx93-iwg50m-sodimm:~# cat /sys/bus/iio/devices/iio\:device1/in_voltage*
    0
    cat: '/sys/bus/iio/devices/iio:device1/in_voltage1_raw': Input/output error
    cat: '/sys/bus/iio/devices/iio:device1/in_voltage2_raw': Input/output error
    cat: '/sys/bus/iio/devices/iio:device1/in_voltage3_raw': Input/output error
    2.442002442

    Let me know your thoughts on this.

    Best Regards,
    Daniel

  • 0 in reply to Daniel Samraj
    TI__Genius 14520 points

    Hi Daniel,

    Apologies, but can I ask for you to attach the Saleae logic capture again? It's easier to see what exact commands are being sent between the device and the MCU.

    Regards,
    Joel

  • 0 in reply to Joel Meraz
    Prodigy 10 points

    Hi Joel,

    Find the attached logic analyzer data

    ADS7950SBRGER-SPI7 (Logic output)SPI Mode-0(19-12-2024).sal

    Best Regards,
    Daniel

  • 0 in reply to Daniel Samraj
    TI__Genius 14520 points

    Hi Daniel,

    Unfortunately the link is expired. Can you resend again? I couldn't take a look at this due to the Christmas holidays last week.

    Regards,
    Joel