I usually only ever find very deep water...
u-boot does all the clever/arch stuff well but I think (for the
not-so-popular Cortex A5) has buggy and undocumented "clever" stuff such
as RNDIS/DFU/etc.
One possibility that occurs to me is to use an additional boot stage, as
an alternative boot, from u-boot to a NuttX "updater app" rather than
the "main" app, that handles this after the normal boot sequence is
interrupted by some method. The "method" is working with u-boot just not
the subsequent firmware download methods.
What I am trying to cater for is the inevitable occasion where a
customer does a firmware update that goes wrong and seems to "brick" the
device, as the "app" nor-flash is corrupted and an in-app updater can't
be run. Current product (AT91SAM9261 based) suffers that as it doesn't
have enough ram to download a complete image before doing the
erase/program function. I expect to be left with MUCH more memory on
this one so can hopefully rely on dfu to RAM before the flash is ever
touched. And enough flash to store 2 images as well.
Plenty of options that mean I don't have to write a PC app and go
through all the signing malarkey etc.
On 01/07/2023 17:41, Gregory Nutt wrote:
On 7/1/2023 10:27 AM, Tim Hardisty wrote:
Lots of work to do a full u-boot replacement, yes. But a basic one
using existing NuttX stuff such as RNDIS, dfu, mtd etc. - for MY
board at least - would not be much work. He said...naively!
You often can't know how deep the water is until you get a little wet.
One thing I would mention. A bootloader is an app alright. But it
may need to use some of internal OS interfaces to control things like
interrupts, MMU, caches, etc. it may need to reset the CPU or other
actions that normal applications would not do. That raises a few
architectural issues (and explains why those primitive loaders are in
the board src/ directory and not in apps/).
Ideally it would run in supervisor mode with a FLAT memory model.
--
Regards,
Tim Hardisty
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