General Notes
References: OMAP4430 Technical Reference Manual (SWPU231AP) pg. 5646+
OMAP Platform has a usbboot mode stage that allows the device to boot into a u-boot image via usb. usbboot can be used to recover from bricks or to test unstable u-boot images without worrying about losing the current u-boot setup.
The following will describe various methods for entering usbboot mode on the Kindle Fire. If you were successful, you should see the following item in lsusb:
Bus 001 Device 025: ID 0451:d00f Texas Instruments, Inc. OMAP4430
Note that the tablet periodically enters and leaves usbboot mode.
This method involves shorting the pin circled in red to ground as the tablet powers on. This method is the viable method if the tablet is bricked (i.e. when the tablet cannot enter u-boot).
Put the tablet in fastboot mode, then run:
$ fastboot oem idme bootmode 4003
If there were no issues, then the tablet should be identifiable with lsusb.
Power on the tablet and use the power button to navigate the menu. Short press to go down and long press to enter.
ADVANCED->TRIGGER USBBOOT MODE->[CONFIRM] RESTART
If you have access to the serial console, then you can enter the u-boot console by pressing ESC in a brief period when the tablet boots into u-boot. The tablet enters the console when the prompt becomes accessible (shown with U-Boot# ).
To enter usbboot mode, run kc1_usbboot.
$ adb shell
# parted /dev/block/mmcblk0
(parted) resize
Partition number? XX
Start? XX
End? XX
....
# mke2fs -T ext4 /dev/block/mmcblk0pXX
$ fastboot boot name_of_boot.img
$ fastboot oem format
| idme | boot mode |
|---|---|
| 4000 | standard boot |
| 4002 | recovery |
| 4003 | usb boot (state persists after reboot; exit by powering down) |
| 5000 | fastboot |
$ fastboot oem idme bootmode <4000|4002|4003|5000>
When the kindle is in usb boot mode, fastboot becomes active only for a short bit after startup. So run the fastboot command before powering the kindle on.
$ adb shell
# idme bootmode <4000|4002|4003|5000>