Investigate FEL as a recovery path - the wiki says A80 supports it #73

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opened 2026-08-30 14:26:49 +00:00 by tiagoagueda · 0 comments

tiagoagueda commented

2026-08-30 14:26:49 +00:00

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The mirror turned up a recovery path we have never considered, and it is directly relevant to
the two P1 issues (#3 hangs in SPL, #5 no remote power control).

What the wiki says

FEL/USBBoot lists the Allwinner A80 as Supported for FEL, both for boot0 and SPL
loading, at roughly 930 KB/s - with the caveat "Not enabled by BROM".

FEL is the boot ROM's USB recovery mode: with the board in FEL, sunxi-fel on a host can upload
and execute U-Boot/SPL over USB without any bootable media at all. That is a fundamentally
different recovery class from everything we have, all of which assumes something on the eMMC or
the SD card is loadable.

The Sunchip CX-A99 page - an A80 board close to a sibling of ours - reports its FEL USB id as
1f3a:efe8, and marks PH16 in its pin table as a "recovery key? (input)".

Why it is worth investigating

Every recovery path this board has assumes the SoC gets far enough to run code from storage:

bootlimit/altbootcmd needs u-boot to run at all
the rescue SD card needs the BROM to load an SPL from it
the serial console needs u-boot or the kernel to be alive

#3 is precisely the case where none of that holds - it hung in SPL, and no software path
existed. It cost a physical power cycle. FEL, if reachable, is the only mechanism that could
recover a board whose on-media bootloader is broken, and it would also make bootloader flashing
(#72) far less consequential.

What to find out

Does the Draco expose a FEL trigger at all? Check PH16 against this board's own
script.bin (the 33-REAL-PINMAP.md method), and look for a recovery pad or key.
What does "not enabled by BROM" mean in practice for sun9i - is FEL entered only on a
specific condition (no valid boot media, a held key), or does it need a fuse/pad?
With the board in FEL, does sunxi-fel recognise sun9i, and can it upload our SPL?
If it works, write it up as a recovery procedure and reference it from #3, #5 and #72.

Caveats up front

FEL needs a USB connection to a host and physical access to trigger, so this is not remote
power control and does not replace #5. What it would buy is that a physical visit becomes
"plug in a cable" rather than "reflash storage on another machine", and that a bad bootloader
stops being able to brick the board.

Note the board's USB 3.0 OTG port is the likely FEL device port; 32-USB3-WORKING.md has the
topology.

From a deep pass over the offline linux-sunxi.org mirror (a80/linux-sunxi.org/wiki-backup, 4095 pages, snapshot 2026-08-29). linux-sunxi.org content is CC BY-SA; the pages named above are the attribution.

The mirror turned up a recovery path we have never considered, and it is directly relevant to the two P1 issues (#3 hangs in SPL, #5 no remote power control). ## What the wiki says `FEL/USBBoot` lists the **Allwinner A80** as **Supported** for FEL, both for `boot0` and SPL loading, at roughly 930 KB/s - with the caveat **"Not enabled by BROM"**. FEL is the boot ROM's USB recovery mode: with the board in FEL, `sunxi-fel` on a host can upload and execute U-Boot/SPL over USB **without any bootable media at all**. That is a fundamentally different recovery class from everything we have, all of which assumes something on the eMMC or the SD card is loadable. The **Sunchip CX-A99** page - an A80 board close to a sibling of ours - reports its FEL USB id as `1f3a:efe8`, and marks **PH16** in its pin table as a *"recovery key? (input)"*. ## Why it is worth investigating Every recovery path this board has assumes the SoC gets far enough to run code from storage: - `bootlimit`/`altbootcmd` needs u-boot to run at all - the rescue SD card needs the BROM to load an SPL from it - the serial console needs u-boot or the kernel to be alive **#3 is precisely the case where none of that holds** - it hung in SPL, and no software path existed. It cost a physical power cycle. FEL, if reachable, is the only mechanism that could recover a board whose on-media bootloader is broken, and it would also make bootloader flashing (#72) far less consequential. ## What to find out 1. Does the Draco expose a FEL trigger at all? Check **PH16** against this board's own `script.bin` (the `33-REAL-PINMAP.md` method), and look for a recovery pad or key. 2. What does "not enabled by BROM" mean in practice for sun9i - is FEL entered only on a specific condition (no valid boot media, a held key), or does it need a fuse/pad? 3. With the board in FEL, does `sunxi-fel` recognise sun9i, and can it upload our SPL? 4. If it works, write it up as a recovery procedure and reference it from #3, #5 and #72. ## Caveats up front FEL needs a USB connection to a host and physical access to trigger, so **this is not remote power control and does not replace #5**. What it would buy is that a physical visit becomes "plug in a cable" rather than "reflash storage on another machine", and that a bad bootloader stops being able to brick the board. Note the board's USB 3.0 OTG port is the likely FEL device port; `32-USB3-WORKING.md` has the topology. --- *From a deep pass over the offline linux-sunxi.org mirror (`a80/linux-sunxi.org/wiki-backup`, 4095 pages, snapshot 2026-08-29). linux-sunxi.org content is CC BY-SA; the pages named above are the attribution.*

tiagoagueda added the

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reliability

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2026-08-30 14:26:49 +00:00

tiagoagueda referenced this issue from a commit

2026-08-30 14:27:46 +00:00

Deep-read the linux-sunxi mirror against the tracker (#73 #74 #75)