Running SeaBIOS on a Chromebook Pixel 2015, by default, does not recognise a plugged in USB 3.0 device attached to a USB 3.0 port or Type C port.
As of 28 Nov, I ran ./flash_chromebook_rom.sh
from
https://johnlewis.ie/custom-chromebook-firmware/rom-download/
to get Johns most current SeaBIOS which will overwrite the RW_LEGACY slot.
This will recognise some but not all USB devices. It would see my USB Phillips drive, just the once, but not the Mushkin drive at all.
I then tried reverting the SeaBIOS back to Google's version. Running Google's ChromeOS recovery, for some reason, does not write or touch the RW_LEGACY slot at all.
John Lewis SeaBIOS was still there after a ChromeOS recovery. Hmm...
I later found out, other Google ChromeOS recovery images do touch and overwrite the RW_LEGACY slot, but not for the Pixel 2015 SAMUS for some reason - bug maybe in the recovery?
With some help from John to extract the shell-ball and manually overwrite the RW_LEGACY slot from the binary inside the ChromeOS recovery image
by following the instructions at
https://johnlewis.ie/extracting-the-shell-ball-rom-using-a-chromeos-image/
Write the hardware ID to get future ChromeOS updates
$ ./gbb_utility --set --hwid="SAMUS XXX-YYY-ZZZ" bios.bin bios.hwid.bin
# dd out 2 megs of the ROM at 4 megs in
$ dd bs=1M skip=4 count=2 if=bios.hwid.bin of=rwlegacy.cbfs
Using the flashrom from John's site as upstream doesn't know anything about flashmap.
$ wget https://johnlewis.ie/Chromebook-ROMs/utils/flashrom -O flashrom.jlewis
$ sudo ./flashrom.jlewis -w -i RW_LEGACY:rwlegacy.cbfs
We now have our original Google version SeaBIOS. But what's this... Before with Google's SeaBIOS, I had no USB 3.0 device got recognised. Now it's recognising all of them, all of the time.
But not quite... I have one USB device, a Philips USB 3.0 device, which for some reason, is appearing not once, but twice in the list of bootable devices, yet only one and only one Philips USB drive is attached.
So it appears, we have half a working solution from Google's own RW_LEGACY, and half a working solution from John's RW_LEGACY.
*********************************************************************** USB 3.0 Devices attached directly to USB 3.0 ports or Type C ***********************************************************************
One - Philips USB 3.0 Flash drive One - Mushkin Ventura Ulta
***************** Google Output *****************
SeaBIOS (version -20150402_151143-build122-m2)
Press ESC for boot menu.
Select boot device:
1. USB MSC Drive Philips USB Flash Drive PMAP 2 AHCI/O: KINGSTON RBU-SUS151S364GD ATA-10 Hard-Disk (61057 M 3. USB MSC Drive Philips USB Flash Drive PMAP 4. USB MSC Drive Mushkin Ventura Ultra
********************** John Lewis Output ********************** Press ESC for boot menu.
Select boot device:
1. USB MSC Drive Philips USB Flash Drive PMAP 2 AHCI/O: KINGSTON RBU-SUS151S364GD ATA-10 Hard-Disk (61057 M
Edward