Their low-level design is much closer to an embedded device like a Raspberry Pi, minus the SD card slot.
...or like a iPhone.
From that article you linked:
Some PC motherboards implement a similar feature as part of a separate chip, which can flash the UEFI firmware from a USB stick without actually turning on the motherboard normally, but this is only common in higher-end stand alone motherboards.
That might be referring to boot-block recovery, and I haven't seen any with a "separate chip" besides the dual-BIOS type; it's in the same flash (just a normally write-protected part) as the rest of the BIOS. The older ones will look for a flashable ROM image on the first floppy drive, but I'm not surprised if the newer ones will do it with USB instead.
How would boot block recovery work without a CPU installed at all?
Because modern bios flashback does indeed read from the USB and write to one of the bios chips without even the CPU in place. Obviously there is some form of micro-controller performing this.
On intel, I suppose it would be possible for the management engine CPU in the chipset to do this, but I doubt intel lets motherboard makers run custom code on that, so if it is not some standardized feature, it could not be that. On AMD Ryzen, I'm not aware of a CPU in the chipset.
This all makes me think there is some other microcontroller somewhere that controls the bios flashback process, which would almost certainly be an extra chip.
> This all makes me think there is some other microcontroller somewhere that controls the bios flashback process, which would almost certainly be an extra chip.
I believe they just have some sort of extra microcontroller wired to a USB port and the SPI flash chip that stores the BIOS, probably with some sort of switch to ensure the host can't touch the SPI flash when the external microcontroller is attempting to flash it.
...or like a iPhone.
From that article you linked:
Some PC motherboards implement a similar feature as part of a separate chip, which can flash the UEFI firmware from a USB stick without actually turning on the motherboard normally, but this is only common in higher-end stand alone motherboards.
That might be referring to boot-block recovery, and I haven't seen any with a "separate chip" besides the dual-BIOS type; it's in the same flash (just a normally write-protected part) as the rest of the BIOS. The older ones will look for a flashable ROM image on the first floppy drive, but I'm not surprised if the newer ones will do it with USB instead.
reply