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SPI interface

jfor jfor
Note: This was originally posted on 10th October 2008 at http://forums.arm.com

Hi all,
   I am using an 180 MHz, 200 MIPS ARM920T.  My question is
How can one have an SPI interface to a device(any)?? What are the steps involved??  :wacko: The O.S used is linux. One thing i noticed is there is no SPI in /dev !!!!! It would be really be helpful if any one can suggest or give any link to solve this.

Thanks,
jfor.
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  • 0 Arm Employee Badge
    Note: This was originally posted on 10th October 2008 at http://forums.arm.com

    Hardware
    Firstly, check the manual (or user guide) for the chip you're using. It's very likely that it does have an SPI peripheral on-chip, but it might not. In addition, it's common for peripherals to share I/O pins as most applications only use a small subset of the available peripherals. Thus, even if it has SPI, you may not be able to use it if you're using other peripherals that share the same pins.

    If you don't have a hardware SPI peripheral, you can probably still interface with SPI because you can control the I/O pins manually from software; this is known as "bit banging". However, the data rate will probably be lower and you'll get more CPU overhead, especially if you want your device to act as a slave. In addition, it'll take longer to implement and debug the SPI interface if you have to do it all manually.

    Linux
    It is likely that you do have SPI on your chip, but that Linux simply doesn't have a driver for it. In this case, you'll probably have to write your own driver. If you're lucky, there may be one available on the net, but I couldn't tell you where to look.

    Also note that Linux may not regard SPI as a device in its own right. It may think of it more as a bus. However, I've never used SPI from Linux so I can't be sure about this. Can anyone be sure of anything in Linux? :-)
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  • 0 Arm Employee Badge
    Note: This was originally posted on 10th October 2008 at http://forums.arm.com

    Hardware
    Firstly, check the manual (or user guide) for the chip you're using. It's very likely that it does have an SPI peripheral on-chip, but it might not. In addition, it's common for peripherals to share I/O pins as most applications only use a small subset of the available peripherals. Thus, even if it has SPI, you may not be able to use it if you're using other peripherals that share the same pins.

    If you don't have a hardware SPI peripheral, you can probably still interface with SPI because you can control the I/O pins manually from software; this is known as "bit banging". However, the data rate will probably be lower and you'll get more CPU overhead, especially if you want your device to act as a slave. In addition, it'll take longer to implement and debug the SPI interface if you have to do it all manually.

    Linux
    It is likely that you do have SPI on your chip, but that Linux simply doesn't have a driver for it. In this case, you'll probably have to write your own driver. If you're lucky, there may be one available on the net, but I couldn't tell you where to look.

    Also note that Linux may not regard SPI as a device in its own right. It may think of it more as a bus. However, I've never used SPI from Linux so I can't be sure about this. Can anyone be sure of anything in Linux? :-)
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