Extracting firmware from a device for reflashing?

Question

OK, so I have a Ubislate 7C+ tablet, and it's screwed up and the Wi-fi is unusable. See Tablet won't connect to any WiFi network anymore, always shows "saved" for details on the problem.

I've tried everything, and I've given up on it. But I'm sure it's a software issue. Factory reset didn't fix the issue either, so I guess the last resort is for me to re-flash my device with the original firmware. The problem here is that the manufacturers (Datawind) have HORRIBLE customer care, and they don't even have any software/driver/firmware downloads for any of their devices. (see petition)

So, since the stock firmware isn't available as a download... is there any way of extracting firmware from a device? I know someone with the exact same device as mine, and it's functioning perfectly. He could help me, but neither of us know any way of doing it. The idea is to basically "leech" the firmware from his device, and then re-flash my device using it. Of course, this whole thing may not even be possible, but I'm lost here.

Thanks.

EDIT: Ok, I just realised that a Nandroid backup would include all system data, and it's a complete system image, including the device firmware. The thing is, such a backup would be huge in size. Is there a way to specifically make a backup of just the firmware of the device or something?

Answer 1

If it isn't the overlapping WiFi channels: a normal Nandroid does include /system and /data, but I think you can just flash them separately. What you're referring as "firmware" is probably the /system partition.

If you guys are using the TWRP recovery, you should be able to add his entire TWRP-created recovery onto your device, boot into TWRP and start a restore, but simply uncheck all partitions except /system. I would make a Nandroid backup before attempting this, as it should work, but I'm not certain.

If you guys aren't using TWRP, it's possible manually via a straight adb dd copy (but...it's not perfect): http://www.modaco.com/topic/327661-how-to-backup-the-systemimg-bootimg-and-recoveryimg/

Basically, as that thread states, on his device, use adb dd to copy a system.img from his phone onto his /sdcard. Then, on your device, use adb dd to paste that system.img onto your phone. Things that need answering: what partition block is /system on (mtdxx) and whether the pull will actually create a full system.img (they note that this method doesn't always copy all of the /system partition).