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MicroZed PMOD Zynq PS MIO I2C controller registers unmapped

jamestkennedy

The design uses Petalinux OpenAMP primarily as a data engine using the Ethernet port to process data and deliver to the microheader. So the MicroZed is a daughter card on a custom PCB that receives the processed data.

However we are also attempting to use the PMOD to connect to an I2C and a GPIO device.

The standard driver for the Zynq PS I2C controller under PetaLinux is Cadence I2C_cadence which operates the PS I2C controller through its registers.

Well the user level /dev/i2c0 writes were not working, so I added a custom module with the i2c_cadence as the basis and connected it to the I2C0 controller in the device tree to see how the driver was failing.

What I found using debug trace is that the I2C controller registers are not connected to their specified address 0xE0004000. Somehow its addresses on the IOP are not mapped. Regardless of what is written all the R/W registers read 0, and obviously the I2C controller function was not being executed.

Other peripherals on the IOP range of addesses UART, ENET work fine.

I am using Vivado 2016.2 and Petalinux 2016.2. The I2C0 is selected on MIO 14, 15 for SCL and SDA respectively, and the device tree specifies the normal 0xE0004000 as the register address for the controller.

Has anyone encountered this and found their mistake? Or any other suggestions?

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  • 0

    Hi James,

    If you have the option of using the PL I2C controller instead, I would recommend doing so.

    Xilinx AR61861 provides some information on why the uses the PS I2C controller is recommended to be implemented from the PL I/Os unless you have some sort of external circuitry implemented as suggested in the Xilinx Answer Record:

    https://www.xilinx.com/support/answers/61861.html

    When you implement I2C in the Zynq fabric, you can add glitch filtering there and those are a standard options for the AXI I2C IP core customization.

    If those are not options for you, it should still be possible to get PS I2C working under Linux.  What do your devicetree entries for I2C look like?

    Regards,

    -Kevin

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  • 0

    Hi James,

    If you have the option of using the PL I2C controller instead, I would recommend doing so.

    Xilinx AR61861 provides some information on why the uses the PS I2C controller is recommended to be implemented from the PL I/Os unless you have some sort of external circuitry implemented as suggested in the Xilinx Answer Record:

    https://www.xilinx.com/support/answers/61861.html

    When you implement I2C in the Zynq fabric, you can add glitch filtering there and those are a standard options for the AXI I2C IP core customization.

    If those are not options for you, it should still be possible to get PS I2C working under Linux.  What do your devicetree entries for I2C look like?

    Regards,

    -Kevin

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  • 0 in reply to zedhed

    Hi Kevin,


    Thanks for replying.

    Unfortunately my  work is confined to the MicroZed SOM,

    And the only PMOD as you know does not allow access wia the PL, only the PS.

    I will apprise my client that the PL using perhaps part of the microheader to a connection on the

    main custom board may be their best option. This board is still under development.

    The DTS entries were generated by petalinunx given the HDF.
     

            i2c0: i2c@e0004000 {
                compatible = "cdns,i2c-r1p10";
                status = "disabled";
                clocks = <&clkc 38>;
                interrupt-parent = <&intc>;
                interrupts = <0 25 4>;
                reg = <0xe0004000 0x1000>;
                #address-cells = <1>;
                #size-cells = <0>;
            };
     

    The driver "cdns,i2c-r1p10" times out on send.

    When I replace it with my custom module. I am able to see that the registers don't work by inserting trace.

    Thanks for you help.

     

    James

  • 0 in reply to jamestkennedy

    &i2c0 {
        clock-frequency = <400000>;
        status = "okay";
    };

     

    in another dtsi file also generated by petalinux