Trouble making PARTITION_WALK work: "Firmware not found" #738
Description
Describe the bug
I'm currently looking into making PARTITION_WALK help boot a Pi4 system if autoboot.txt got messed up somehow. It seems I'm doing something wrong as I can't get the EEPROM to load the firmware files from an otherwise bootable partition.
Here's the output if autoboot.txt directly specifies boot_partition=3:
[all]
tryboot_a_b=1
boot_partition=3
[tryboot]
boot_partition=2
The Pi boots correctly after loading start4.elf and fixup4.dat.
Now when I manually edit autoboot.txt to switch both partitions around, so it defaults to boot_partition=2, which points at an empty formatted FAT partition, the following failed boot happens:
It looks like:
- Tries partition 2, which immediately fails. As I understand it, this then triggers the
PARTITION_WALKfallback and it scans all other partitions. - Tries partition 1 (the one with autoboot.txt in it) -> fails as expected
- Tries partition 2 again -> fails a second time, as expected
- Tries partition 3:
- It loads config.txt and one of the included .txt files
- Looking at the first screenshot above, the next step should be loading
start4.elf, which doesn't happen. Instead the boot process fails.
One difference I noticed is that the fw: line shows different files. The working boot process shows fw: start4.elf fixup4.dat, while the non-working shows fw: start.elf fixup.dat.
According to the documentation, PARTITION_WALK will check each partition in turn (up to 8 and wrapping to 0) to see if it is bootable (contains start4.elf on a Pi4, or config.txt and a suitable device-tree on Pi 5 or newer).
Here's the files on the top-level directly of partition 3:
total 71825
-r--r----- 1 root root 18693 Aug 14 08:38 COPYING.linux
-r--r----- 1 root root 1594 Aug 14 08:38 LICENCE.broadcom
-rw-rw---- 1 root root 784 Aug 14 08:38 README.txt
-rw-rw---- 1 root root 41 Aug 14 08:38 VERSION.txt
-r--r----- 1 root root 155 Aug 14 08:38 autorun.inf
-r--r----- 1 root root 30660 Aug 14 08:38 bcm2708-rpi-b-plus.dtb
-r--r----- 1 root root 30019 Aug 14 08:38 bcm2708-rpi-b-rev1.dtb
-r--r----- 1 root root 30357 Aug 14 08:38 bcm2708-rpi-b.dtb
-r--r----- 1 root root 29960 Aug 14 08:38 bcm2708-rpi-cm.dtb
-r--r----- 1 root root 31837 Aug 14 08:38 bcm2708-rpi-zero-w.dtb
-r--r----- 1 root root 29970 Aug 14 08:38 bcm2708-rpi-zero.dtb
-r--r----- 1 root root 32354 Aug 14 08:38 bcm2709-rpi-2-b.dtb
-r--r----- 1 root root 32129 Aug 14 08:38 bcm2709-rpi-cm2.dtb
-r--r----- 1 root root 32503 Aug 14 08:38 bcm2710-rpi-2-b.dtb
-r--r----- 1 root root 35330 Aug 14 08:38 bcm2710-rpi-3-b-plus.dtb
-r--r----- 1 root root 34695 Aug 14 08:38 bcm2710-rpi-3-b.dtb
-r--r----- 1 root root 33684 Aug 14 08:38 bcm2710-rpi-cm0.dtb
-r--r----- 1 root root 32266 Aug 14 08:38 bcm2710-rpi-cm3.dtb
-r--r----- 1 root root 319 Aug 14 08:38 bcm2710-rpi-kms.txt
-r--r----- 1 root root 33672 Aug 14 08:38 bcm2710-rpi-zero-2-w.dtb
-r--r----- 1 root root 33672 Aug 14 08:38 bcm2710-rpi-zero-2.dtb
-r--r----- 1 root root 56247 Aug 14 08:38 bcm2711-rpi-4-b.dtb
-r--r----- 1 root root 56251 Aug 14 08:38 bcm2711-rpi-400.dtb
-r--r----- 1 root root 39913 Aug 14 08:38 bcm2711-rpi-cm4-io.dtb
-r--r----- 1 root root 56768 Aug 14 08:38 bcm2711-rpi-cm4.dtb
-r--r----- 1 root root 53510 Aug 14 08:38 bcm2711-rpi-cm4s.dtb
-r--r----- 1 root root 78568 Aug 14 08:38 bcm2712-d-rpi-5-b.dtb
-r--r----- 1 root root 78572 Aug 14 08:38 bcm2712-rpi-5-b.dtb
-r--r----- 1 root root 78528 Aug 14 08:38 bcm2712-rpi-500.dtb
-r--r----- 1 root root 79286 Aug 14 08:38 bcm2712-rpi-cm5-cm4io.dtb
-r--r----- 1 root root 79352 Aug 14 08:38 bcm2712-rpi-cm5-cm5io.dtb
-r--r----- 1 root root 79327 Aug 14 08:38 bcm2712-rpi-cm5l-cm4io.dtb
-r--r----- 1 root root 79393 Aug 14 08:38 bcm2712-rpi-cm5l-cm5io.dtb
-r--r----- 1 root root 78576 Aug 14 08:38 bcm2712d0-rpi-5-b.dtb
-r--r----- 1 root root 52476 Aug 14 08:38 bootcode.bin
-r--r----- 1 root root 176 Aug 14 08:38 cmdline.txt
-r--r----- 1 root root 6 Aug 14 08:38 compat.lzma
-r--r----- 1 root root 6 Aug 14 08:38 compat.sig
-r--r----- 1 root root 6 Aug 14 08:38 compat.upd
-r--r----- 1 root root 6 Aug 14 08:38 compat.ver
drwxrwx--- 2 root root 512 Aug 14 08:38 config
-r--r----- 1 root root 4152 Aug 14 08:38 config.txt
-r--r----- 1 root root 5459 Aug 14 08:38 fixup4.dat
-r--r----- 1 root root 10295 Aug 14 08:38 fixup_x.dat
-r--r----- 1 root root 295015 Aug 14 08:38 ibhosted.ico
-r--r----- 1 root root 45 Aug 14 08:38 info.txt
-r--r----- 1 root root 11498881 Aug 14 08:38 init.gz
-r--r----- 1 root root 7387968 Aug 14 08:38 kernel.img
-r--r----- 1 root root 7738504 Aug 14 08:38 kernel7.img
-r--r----- 1 root root 9608253 Aug 14 08:38 kernel8.img
drwxrwx--- 2 root root 5120 Aug 14 08:38 overlays
-r--r----- 1 root root 7249 Aug 14 08:38 release.sig
-r--r----- 1 root root 29417472 Aug 14 08:38 stage2.img
-r--r----- 1 root root 2266048 Aug 14 08:38 start4.elf
-r--r----- 1 root root 3737320 Aug 14 08:38 start_x.elf
-r--r----- 1 root root 99352 Aug 14 08:38 vl805.bin
-r--r----- 1 root root 65 Aug 14 08:38 vl805.sig
Judging from the documentation alone, this should work as start4.elf does exist. I also added empty files start.elf, start4x.elf, fixup.dat and fixup4x.dat but still get the "Firmware not found" error. I'm clearly missing something.
Steps to reproduce the behaviour
Don't have an easy way yet.
Device (s)
Raspberry Pi 4 Mod. B
Bootloader configuration.
[all]
BOOT_UART=0
WAKE_ON_GPIO=1
POWER_OFF_ON_HALT=1
MAX_RESTARTS=200
BOOT_ORDER=0xf1
ENABLE_SELF_UPDATE=1
DISABLE_HDMI=0
NET_INSTALL_ENABLED=0
PARTITION_WALK=1
[partition=32]
PARTITION=0
HDMI_DELAY=0
NET_INSTALL_ENABLED=1
NET_INSTALL_KEYBOARD_WAIT=1200
System
# vcgencmd bootloader_version
2025/07/17 09:26:45
version 3c6288961a69b5cc682966c88f9a1aaa3ceb5fe0 (release)
timestamp 1752740805
update-time 1755087947
capabilities 0x0000007f
# vcgencmd version
Jul 17 2025 17:31:44
Copyright (c) 2012 Broadcom
version a668b6e6edce3274de221324b93cb8741e4a7f7c (clean) (release) (start)
# uname -a
Linux info-beamer-60262259 6.12.41-v8+ #1897 SMP PREEMPT Fri Aug 1 12:20:46 BST 2025 aarch64 GNU/Linux
Bootloader logs
Don't have those yet, but I'll see if I can capture NETCONSOLE next.
USB boot
No response
NVMe boot
No response
Network (TFTP boot)
No response