On Sat, Mar 04, 2017 at 06:40:57PM -0500, Joe Gidi wrote:
> After jsg@ mentioned that booting a Raspberry Pi 3 from a USB device
> might be
> possible, I decided to find out how deep the rabbit hole is.
> As it turns out,
> it's currently a bit convoluted, but it can be made
> to work with OpenBSD.
> First off, USB boot support is just now getting fully ironed out.
> You'll need
> to update the firmware on your Pi to make it work. I
> installed the latest
> (2017-03-02) Raspbian image to an SD card and
> booted the Pi from that. While
> booted in Raspbian, update the
> firmware:
>
> sudo apt-get update
> sudo apt-get
> install rpi-update
> sudo rpi-update
>
> It's then necessary to actually enable USB
> boot support. Add the
> following 2 lines to /boot/config.txt to enable USB boot
> mode and set
> a 5-second timeout to allow time for USB device initialization:
> program_usb_boot_mode=1
> program_usb_boot_timeout=1
>
> NOTE: Apparently these
> variables are set in the Pi's OTP memory, which
> means once they're set, they
> can't ever be unset.
>
> Reboot for the changes to take effect. At this point the
> Pi should be
> ready to support USB booting.
>
> While you still have a working
> Raspbian install, grab a copy of the
> /boot/bootcode.bin and /boot/start.elf
> files for later use; apparently
> we need these special versions of those two
> files for USB boot
> support. At this point we're done with Raspbian and can
> shut it down
> to install OpenBSD.
>
> Next, write the OpenBSD miniroot60.fs to an
> SD card, plug in your USB
> drive, and boot the Pi. You should be greeted with
> the usual OpenBSD
> installer, and you should be able to install to your USB
> drive
> (probably sd0). Once the installer is done, run 'halt', unplug the Pi,
> and remove the SD card and USB drive.
>
> To make your USB drive bootable, you'll
> need to plug it into another
> system and mount its 'i' partition (the FAT32
> boot partition) to make
> a few changes. Replace the bootcode.bin and start.elf
> files with the
> ones from Raspbian, and add the u-boot.bin file from the 'i'
> partition
> of your miniroot60.fs SD card.
>
> With those changes made, your Pi
> should be able to boot OpenBSD
> directly from a USB drive with no SD card
> needed. Note that it seems
> to take around 10 seconds for the Pi to reach the
> OpenBSD bootloader
> and fire up the kernel.
>
> Hope this information is helpful
> to someone...
>
> --
> Joe Gidi
> j...@entropicblur.com
>
> "You cannot buy skill."
> -- Ross Seyfried
Thanks, I'll try this out soon,
Some notes of things I saw when trying to boot from a sd-card using
various a USB devices to install to:
Some USB devices do seem to hang the rpi3 sometimes while u-boot is
scanning the usb bus, in my case an old USB flash stick.
With a disk enclosure (2.5" usb bus powered with spinning disk), the
hangs did not occur. But I saw another problem that looked to be
caused by the reset of the usb bus while the kernel was booting (from
sd-card). The disk enclosure did not get recognized in time when the
kernel reached the ask root device questions, making it imposible to
select the usb drive as boot device.
I manged to boot the machine using an externally powered enclosure
with a 3.5 disk. I'll be buying a SSD today to see how that goes.
-Otto
