Booting a Raspberry Pi from USB (was: Re: Is it a brick?)

[Liam Proven]

On Mon, 11 Oct 2021 at 21:37, Gene Heskett <gheskett at shentel.net> wrote:
>
> Never tried. It was originally, when the pi3b was relatively new yet,
> recommended I write the sd card with it

Aha!
> which upchucked before it was
> done, and never made a bootable u-sd.

Huh. That's odd, but yeah, as per my previous, not _entirely_ unexpected.

RasPis are great but they are weird little machines with a wildly
nonstandard architecture unlike anything else today.

But that's OK with me. I remember when all the fun home computers were
all totally dissimilar to one another. :-)

>   DD just worked, that got me
> booted into raspbian.

Yup, the simple methods are the best.

>  But the stock raspbian kernel's latency was
> millisecond plus. Totally unusable. And you could watch the screen being
> redrawn.  This was on a pi3.

Yeah, the performance of the RasPi 2 and RasPi 3 was not great. Linux
is just a bit too heavyweight for an ARM Cortex-A53.

It's a shame other non-Unix OSes didn't get in there while the
machines were still sluggish. There's a whole bunch of FOSS OSes that
would be nice to have on a Pi -- AROS (Amiga-alike), Haiku
(BeOS-alike), Oberon (Professor Niklaus Wirth's final project,
basically Pascal v4).

Now the Pi 4 as you say is quick enough.

> Eventually a new enough preempt-rt kernal
> came out that did support its video, so I stripped it to armv7 stuff and
> built it on the pi, took around 10 hours. By then I had been banned from
> their forum so I was on my own

:-(

> so I took the boot stuff apart to see
> what I needed to run the preempt-rt kernel. Made a partition on an SSD,
> and populated it with the stuff it needed, and made a tarball of it,
> just under 30 megs uncompressed. Wash, rinse, and repeat from wheezy,
> jessie, stretch and now buster versions of raspbian.

Excellent work! I'm impressed.

> Exported that tarball, generated on the pi, to one of my linux pc's where
> I had a card writer. Extracted the u-sd from the pi and plugged it into
> the card reader, unpacked that tarball to it, overwriting anything that
> was in the way. Sync'd the card and ejected it, took it back to the pi3,
> booted flawlessly. Decent latency in the sub 50 microsecond category.
> Ran my lathe with it that way for a couple years.

Excellent stuff.

> But the pi3b was
> dragging its tongue on the floor doing it.

I bet it was.

> Then the pi4b came out so I ordered a 2g version. Changed the kernel for
> the new gpio setup, and repeated that install. That was February last
> year. pi4 is a hell of a lot faster, and it all Just Works.

Glad to hear it.

> I know you
> can make debs that will install a new kernel, but despite asking how to
> do that, I was banned for asking.

:-(

> But on the pi4b with usb3 interfaces to the SSD's, I can build a new
> kernel in about an hour.

I'm running a Pi 4 here as a home fileserver, with 4 USB3 hard disks
attached to it. It runs really very nicely for a sub-$100 computer,
and the ZFS RAIDZ array can soak up about a gigabyte of data per
minute, which is fast enough for my purposes.

> And its latency, running overnight to collect the absolute worst case is
> around 50 microseconds unless I start firefox, normal is about 12
> microseconds. Not too shabby for a computer that according to a
> kilawatt, is running on 8 watts.  The monitor draws 11 watts.

Impressive performance.

> Take care Liam. I Hope I haven't bored you too much. ;o)

It was fascinating!

-- 
Liam Proven ~ Profile: https://about.me/liamproven
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