Monday, October 14, 2013

General Advice on Flashing Firmware

I guess relatively few people are as paranoid as I am, but given the ease and speed of flashing from CrOS or Linux on the C710 itself, I suggest the following process:

1. Before you flash an image, create a backup (BACKUP.BIN) of the current firmware and generate an md5sum for it.
2. Now, generate an md5sum for the image you're about to flash, let's say NEW_FW.BIN.
3. Flash the image.
4. Even if everything appears to go perfectly, create a backup of the firmware again, i.e. READBACK.BIN and either compare it to NEW_FW.BIN  or (I prefer to) generate an md5sum for READBACK.BIN and compare the md5sums of the two.

This will allow you to revert to the state of the firmware before you started (with your BACKUP.BIN) and guarantee that the EEPROM now contains what you intended.

4 comments:

  1. I've been thinking about trying the coreboot firmware, but if I understand right, I need to make a backup of my current firmware first right? And to do that I have to make a jumper? How do I do that and what do I jump? I couldn't find any information about that.

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  2. Sorry for the sluggish response, I had surgery yesterday so I've been a little sedated, still am in fact.

    Both procedures require that you disable hardware write-protect. This means that you have to open your C710 and bridge a jumper (socket with 2 pins inside). Refer to this page to gain access to the internals and to locate the jumper:

    http://www.chromium.org/chromium-os/developer-information-for-chrome-os-devices/acer-c7-chromebook

    The write-protect jumper is under a piece of black plastic tape. Click on the left-hand photo to enlarge it, the location is marked. Here are a couple of close ups:

    https://docs.google.com/file/d/0Bzig09VSdjW1X0hDd2ZRbDhvZUE/edit?usp=sharing
    https://docs.google.com/file/d/0Bzig09VSdjW1Mlp5RVA1cWd1b1k/edit?usp=sharing

    To bridge the jumper, my method was to take a tiny square of aluminum foil (about 1/4 inch), bring the corners up to meet (now you've got an X), then crush this gently into a loose cylinder about the size of the jumper socket. The intent is to create an aluminum U with the pins piercing the bottom when it's in place. You want it to protrude slightly from the socket, so you can remove it easily.

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    Replies
    1. Hope you recover well!

      How long do I need to leave the jumper on? It seems like I remember reading somewhere that I had to take it off immediately after I backup the BIOS and shutdown?

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  3. Thanks, I'm doing pretty well, just a little slower than usual!

    In general, you should bridge the jumper with the C710 powered off, boot up, follow the procedure I outlined above, shutdown and remove the jumper as a precaution before you try to boot the new firmware.

    The two critical things to remember are:
    1. to bridge the jumper (disable hardware write-protect) BEFORE you backup the stock firmware and
    2. to remove the jumper (re-enable hardware write-protect) BEFORE you boot the new firmware.
    Just proceed carefully, following instructions precisely and you should be fine.

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