I'm testing Coreboot with SeaBIOS as payload on my old Alix.2C2. When trying to boot from an USB device I get the following error:
Searching bootorder for: /pci@i0cf8/usb@f,5/storage@2/*@0/*@0,0
Searching bootorder for: /pci@i0cf8/usb@f,5/usb-*@2
ehci_send_pipe qh=0x000ecf00 dir=0 data=0x00006cf9 size=31
ehci_send_pipe qh=0x000ecf80 dir=128 data=0x00006dc4 size=36
ehci_send_pipe qh=0x000ecf80 dir=128 data=0x00006cec size=13
WARNING - Timeout at ehci_wait_td:516!
ehci pipe=0x000ecf80 cur=00000000 tok=00000000 next=6b40 td=0x00006b40 status=d0d80
USB transmission failed
Unable to configure USB MSC drive.
phys_free f6030 (detail=0x0f7688a0)
Unable to configure USB MSC device.
Google found a thread from 2012 [1] where someone had the same problem with this particular chipset. Unfortunately he was unable to resolve the issue.
Attached you will find the complete logs from both Coreboot and SeaBIOS.