Booting from USB on RPI3

[bob prohaska]

On Fri, Apr 24, 2020 at 03:09:35PM -0700, Mark Millard wrote:
[huge snip, hope nothing vital was lost]
> 
> Now that using both the microsd card and USB drive
> as a pair to boot has been shown to work, have you
> made the USB drive match what is used on from
> the microsd card (such as the msdos file system)
> and checked what the USB drive does without
> involving the microsd card?
> 
> (Although, I wonder if the "10 sec" issue ends up
> involved, possibly blocking this way of working.)
 
No. If there's no microSD at all the Pi3B is simply inert
on power-up. No rainbow screen, no serial console, nothing. 
The OTP boot-from-usb bit is set according to Raspbian,
so mine is one of the Pi3's that requires a microSD card.

If there's no microSD filesystem to fall back to, maybe
u-boot would keep trying until the USB hard drive woke up.
Somebody also mentioned recompiling u-boot with a longer 
timeout, not an unreasonable step.  For now I'll declare 
victory and retreat 8-)

I gather the Raspberry Pi Foundation didn't more widely 
publicise the boot-from-usb feature because it didn't work 
with a too-large fraction of USB storage devices. Having 
now seen the exercise in person, I understand their motives. 
There was absolutely no chance of success without the vast
amount of help I got on this list.  

With my thanks,

bob prohaska