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Mapping linux driver to GPIO

Former Member

Hi All,

I have currently mapped two GPIO to be used with slave devices to operate with I2C. I also have checked the mapped GPIO by writing 1/0 through command like and checking the signal through an oscilloscope.

I would like to map the I2C driver already there in the kernel to be used with these two GPIO pins.

Question:

1. How do I map the linux kernel I2C driver to GPIO so that I can communicate with the slave devices.

2. There are 4 i2c commands: i2cdetect, i2cdump, i2cget, i2cset. Is there any documentation on how to use them?

  • 0

    Hi yathindra,

    I guess I am a little confused about what you are trying to accomplish.  Are you only using the GPIO to show that you can toggle them successfully externally on the board?  If so, then I suggest removing the GPIO to those pins and instead using the Xilinx AXI I2C IP to connect the processor to the external I2C slave devices.

    You can find more information on how to implement the driver from the software side here:

    http://www.wiki.xilinx.com/Linux+I2C+Driver

    The driver mapping that needs to occur in order to reach the AXI I2C controller happens within the device tree.  Here is an example devicetree entry for an I2C block implemented within the Programmable Logic:

    axi_iic_0: i2c@41600000 {
                            #address-cells = <1>;
                            #size-cells = <0>;
                            compatible = "xlnx,xps-iic-2.00.a";
                            interrupt-parent = <&intc>;
                            interrupts = <0 29 4>;
                            reg = <0x41600000 0x10000>;
                    };

    We have had good results using i2cdetect and i2cdump by simply following the man page for these commands:

    http://linux.die.net/man/8/i2cdetect

    There is also the possibility of doing I2C over GPIO using this Linux driver but that practice is definitely not recommended for use in a real world application:

    https://lwn.net/Articles/230571/

    Regards,

    -Kevin

  • 0 in reply to zedhed

    Thanks for the reply. I am currently working on these lines. 

    To clarify, I am currently using GPIO connected to slave devices through I2C bus.

     

    I am kind of confused right now about the entire procedure. 

    Since there is an I2C driver already in the kernel, may I know why I need to use/modify http://www.wiki.xilinx.com/Linux+I2C+Driver  ?

    Wont a simple mapping of address space, probably by using mmap of the inbuilt I2C and address of GPIO be enough?  That also brings us to the question, how to actually do data transfer using i2cset and i2cget. From the linux man pages, I understood that they are just helper functions.

    Please share your thoughts on this.

    Thanks

  • 0

    Hi yathindra,

    Using the I2C driver is going to make your life a lot easier since the interface details of I2C get abstracted way by this driver making it much simpler to write your user space application.  You won't need to perform MMAP operation and hassle with the timing of GPIO to implement I2C if you simply use one of the I2C controllers (either PS I2C or PL AXI IIC) and the corresponding driver.

    We have an example of how to use PL I2C from Linux and you can download this "Wind River Pulsar Linux OS with I2C Peripheral Integration" tutorial from the reference designs page:

    http://microzed.org/support/design/13591/116

    This will involve making sure that the appropriate I2C driver is built into the kernel, there is a valid device tree entry for the I2C controller instance, and that the userspace application is accessing the I2C driver correctly.

    Regards,

    -Kevin

  • 0

    Hi yathindra,

    For the i2c commands (i2cdetect, i2cdump, i2cget, i2cset) I would recommend looking at the man page for these commands:

    http://linux.die.net/man/8/i2cdump

    Regards,

    -Kevin

  • 0

    Hello,

    I was able to read/write from the external device (EEPROM connected with I2C) using the Xilinx driver  http://www.wiki.xilinx.com/Linux+I2C+Driver , however I have the following two questions, 

    1. Is the driver specific to EEPROM alone?  I would like to know if the same can be used with other I2C devices like a DAC, LCD etc? I cannot actually test other devices for a few days until I get the devices though. 

    2. This driver does read and write, is there any easy way to probe for I2C devices as well?

    Currently I am checking /sys/class/i2c/ for the devices present and including them in the driver code..

    Thanks