[U-Boot-Users] Safe firmware updates

[Ian Ridge]

Thanks for your comments


>In message
<9D8FC3304AA0924E9CD0A211DFEDCBAB0164D7AF at bespin.apdcomms.co.uk> >you
wrote:
>> 
>> We are implementing facility for automatic firmware upgrades (either
the
>> Linux uImage or cramfs) on our embedded device. However there is a
.> requirement that the device is not broken by (the user for example)
>> disconnecting the power supply at any stage during the flash update.

>This is not new. It's actually a astandrard requirement.

>> In the absence of a backup battery, I guess the boot loader would
have
>> to be modified to cope with this. Has anybody produced a solution
>> already?

>There is no need to change anything. U-Boot is perfectly  capable  of
>supporting such requirements.


That's great news, but how?

>> 4) 'update' routine checks specified flash location for new upgrade
>> image with valid CRC. If no image found or has bad CRC it returns,
>> control passes to next command in bootcmd, and Linux boots normally.
>> 
>> 5) 'update' routine erases target area of flash, and then copies
content
>> of upgrade image to target location.

>Why would you do that if the new image is already in flash? 

I considered of doing it like this because we have limited flash space
and need to re-use a flash partition normally usually for logging data.
We haven't got enough space to store 2 copies of the uImage, and 2
copies of the cramfs file system. We could automatically change the
mtdparts parameter in bootargs after each update to reflect this, but
this would mean a change to u-boot and its getting too complicated
again.

>Just swap
>boot addresses...

I understand I could put a second bootm command in bootargs to
automatically switch boot address, but how would I swap cramfs file
systems in a safe way? The flash partition used for the cramfs is
currently specified using 'root=/dev/mtdblock2' in bootargs, but I don't
see how to make u-boot change this to say 'root=/dev/mtdblock3
automatically'.
 
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