https://github.com/mkj/rpi-flipflop
Raspberry Pi Boot Flipflop
https://github.com/mkj/rpi-flipflop
Last synced: 11 months ago
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Raspberry Pi Boot Flipflop
- Host: GitHub
- URL: https://github.com/mkj/rpi-flipflop
- Owner: mkj
- License: mit
- Created: 2015-04-10T12:02:46.000Z (about 11 years ago)
- Default Branch: main
- Last Pushed: 2019-03-01T14:55:27.000Z (over 7 years ago)
- Last Synced: 2025-05-06T12:38:07.156Z (about 1 year ago)
- Language: C
- Size: 20.5 KB
- Stars: 10
- Watchers: 4
- Forks: 1
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
# Raspberry Pi Flipflop
This is a replacement for the old kernel\_emergency.img that old Raspberry Pi
firmwares used, see http://elinux.org/RPI_safe_mode .
It lets you toggle booting two different partitions (kernels/distros/images)
depending on the state of GPIO pin 3.
You specify a "normal partition" and a "safe partition". Usually the Raspberry Pi
will boot the normal partion. If GPIO pin 3 (pin 5 on the physical header) is
held to ground it will boot the safe partition.
I am using this in conjunction with a hardware watchdog that toggles the "safe boot"
GPIO pin every few hours https://github.com/mkj/pihelp . That ensures that I
can access the device even if I break one of the partitions - I have a fallback
rescue partition.
At the time of writing (April 2015) this has been tested on a 512MB Raspberry Pi B (not +) with Linux 3.18.7
Matt Johnston
## Installing
- Get `flipflop.initramfs`. There's a prebuilt binary at
https://matt.ucc.asn.au/rpi-flipflop/flipflop.initramfs or
build flipflop by running `make`. I've been cross-compiling from a
x86 Ubuntu box, I assume building on the Raspberry Pi itself should work too.
- Partition and set up a SD card
- mmcblk0p1 - vfat, perhaps 40MB. This is only used by flipflop.
I'll call this the "first boot partition", it has
a Linux kernel and the flipflop initramfs (and other boot files).
- "normal boot" partition, has all the boot files for the normal distro (eg /boot from raspbian)
- "safe" partition, also has all the boot files but for the safe distro. Its
cmdline.txt probably points at a different root partition to normal.
- The root partitions for each of the normal/safe partitions
- Anything else (perhaps config file partition, see below)
- Set up a vfat mmcblk0p1 partition with the contents of
https://github.com/raspberrypi/firmware/tree/master/boot
or /boot from recent Raspbian.
```
COPYING.linux cmdline.txt issue.txt
LICENCE.broadcom config.txt kernel.img
LICENSE.oracle fixup.dat kernel7.img
bcm2708-rpi-b-plus.dtb fixup_cd.dat overlays/
bcm2708-rpi-b.dtb fixup_x.dat start.elf
bcm2709-rpi-2-b.dtb flipflop.initramfs start_cd.elf
bootcode.bin start_x.elf flipflop.txt
```
- Copy `flipflop.initramfs` to the first boot partition. Edit config.txt and add a line
```
initramfs flipflop.initramfs followkernel
```
- Create a file `flipflop.txt` on the first boot partition to customise the config.
An example to boot mmcblk0p5 in normal mode or mmcblk0p8 in safe mode
```
normal_bootpart 5
safe_bootpart 8
```
You can also point it at further config files to parse - this is useful if you want
an editable config file on a different partition to avoid ever editing your
mmcblk0p1 for safety.
```
normal_nextconf mmcblk0p2:vfat:nextconf.txt
safe_nextconf mmcblk0p2:vfat:flipflop.txt
```
The default configuration is hardcoded near the top of [flipflop.c](flipflop.c)
- Install normal distros to your normal and safe partitions. It should now work.
## How it works
Flipflop boots a Linux kernel that runs flipflop as /init in an initramfs.
It looks at the GPIO pins then sets the Raspberry Pi's reboot parameter
`/sys/module/bcm2708/parameters/reboot_part` as appropriate.
Then it reboots and the device boots whichever partition you chose. It adds a few seconds
to the boot time.
This works the same as [NOOBS](https://github.com/raspberrypi/noobs) - it uses the same
parameter to automatically boot the installed distro if the "safe mode" pin isn't held.
The "separate config partition" idea came from NOOBS too.