[U-Boot] stopping u-boot from booting an old image in RAM.

[Wolfgang Denk]

Dear "David Collier",

In message <memo.20091021160842.4412A at postmaster+dexdyne.com.cix.co.uk> you wrote:
> If I boot this unit, then remove the SD card it booted from and reset it,
> it happily boots some Linux image which is lying around in memory.

Maybe you should start reading the documentation?

> It even does it after a short power-off power-on sequence.

It takes time until memory loses it's content, and as long as the
checksums are OK the image is still valid. It is up to you to provide
a sane boot command which checks for error code.

> I think that's horrible behaviour.

Indeed - but that's not U-Boot's fault, it's horrible programming by
the user, i. e. yourself.

> I was told I could use && instead of ; between the commands in the
> bootcmd string to stop this, but that barfed, and then I was told that

You really should read the documentation, at least the FAQ, for
example "14.2.16. How the Command Line Parsing Works" at
http://www.denx.de/wiki/view/DULG/CommandLineParsing

> maybe && only existed if "scripting is enabled"

Whoever told you that used poor language. What he meant was: if the
Hush shell is configured as command line parser for your board.

> Could anyone please talk me through the steps of either
> 
> 1. doing what it takes to enable this && feature, so that if it fails to
> find the card, it doesn't go on and try to boot.

To enable the hush shell, you have to set (at least) the
CONFIG_SYS_HUSH_PARSER configuration option in your board config
file. But even the old, simple command line parser can be used to do
what you want. Just RTFM.

> 2. something else that will do it, such as so effectively buggering up an
> image that has been booted from that it will never be re-used

I cannot parse that. If an image has been booted, U-Boot is gone and
out of the way, and whatever code was in the image is running.

Best regards,

Wolfgang Denk

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