Theo  wrote:
> bob prohaska  wrote:
>> When booting Buster on a Pi3B+ it seems that u-boot finishes
>> before there's any chance of text input on the console.
>>
>> How does one make u-boot pause and accept input so the
>> boot can be redirected from microSD to USB when starting
>> Buster?
>
> The default Pi boot process uses firmware running on the GPU and loaded from
> SD card (except Pi 4 where there's flash ROM), so the ARM isn't operational
> until the kernel is loaded.  This isn't u-boot.  It is possible to load a
> 'kernel' which happens to be the u-boot binary, and then u-boot selects
> where to load the next stage from.
>
> AIUI the default Raspbian doesn't use u-boot.  It is possible to put it on
> the SD card, in which case it provides a serial console.  For example:
> https://andrei.gherzan.ro/linux/uboot-on-rpi/
>
Sounds like the key is having a serial console. I don't, on the machine
in question, and can't easily set one up.

On FreeBSD machines that _do_ have a serial console it's possible to interrupt
u-boot by hitting the spacebar and tell it to look for a USB mass storage
device with:
usb reset
Once found, the command
run bootcmd_USB0
will boot from the USB device.

I was hoping to do something similar for the machine running RaspiOS, which
is isolated with no place to set up a serial console, just hdmi and keyboard.
It's still possible to simply insert the microSD card and let it take over,
like an old-fashioned boot floppy. I guess that will have to do for now.

Thanks for writing!

bob prohaska

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