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Finding GPIO pins on motherboard

Discussion in 'Electronic Repair' started by [email protected], Jul 12, 2007.

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  1. Guest


    I've just started working with Linksys routers and loading open source
    Linux on them for an enhanced feature set and I've found problem lies
    with the limited amount of flash memory that these units have. To
    increase the router's available flash, you have to hack the mother
    board by finding the GPIO pins and running wires from them to an SD
    slot. The instructions for this procedure for the WRT54G with a
    BROADCOM BCM47are here:

    My problem is that I have a newer WRT350N router with a BROADCOM 4705
    cpu. What would be a generalized procedure for finding the GPIO pins
    for this motherboard?

  2. hath wroth:
    From the above URL, I find:
    A good way to test the pin allocations is with the gpio utility
    and a script to toggle the GPIO pin periodically, then search for
    the pin with a digital multimeter or oscilloscope probe. I toggled
    the pins with the following single line in the shell (example for
    GPIO 5):

    while true
    gpio enable 5
    sleep 1
    gpio disable 5
    sleep 1

    (Note that I fixe the shell script syntax slightly)

    Basically, run the GPIO utility supplied, run the above script, get
    out your oscillosocpe, and start testing pins. There's a chance that
    the GPIP utility might not work, but you'll find out soon enough.

    I think this is one case where trial and error might be more useful
    than digging for the info. If all else fails, find someone with a
    Broadcom 4705?? data sheet, that hasn't signed an NDA, and it should
    show the pins on the pinout diagram.
  3. Guest

    I did it on a WAP54G V31 (the link to my site is on the above link),
    for the SDcard you need 4 basic signals, DI DO Clock and CE.
    The obvious was to use the LEDs (2 are on a GPIO port) and switches.
    Problem was there were only 2, SES and reset switch.
    In this version Linksys polls the reset and SES switches!!
    The polling routines (that are non-GPL anyways) need to be removed..
    the GPIOs can be used.
    Maybe that model of yours has more switches.
    To find which GPIO is connected to what, you need to make a serial
    port connection, or a telnet connection by uploading new firmware,
    run gpio from that.
    There is a gpio.c test routine C source you can download: a gpio test
    routine that you
    Here you can read more about using it:

    Download the Linksys sources for your box from

    and make sure you can compile it, and have a backup of the firmware.
    The best is if you can make a backup of the whole FLASH via JTAG,
    but I dunno if there is JTAG soft for your box, I had to modify some
    to make it
    work on my processor, see my site.
    Without the JTAG debrick I would have had to throw my box in the
    It stopped working after downloading _others_ firmware from the web.
    This because mine had only 2 MB FLASH,.
    Be warned.
    More here:
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