Updating the firmware is possible using the internal method, where the updates happen from a running system, or using the external method, where the system is in a shut down state and an external programmer is attached to write into the flash IC.
This method using flashrom is available on many platforms, as long as they aren't locked down.
There are various protection schemes that make it impossible to modify or replace a firmware from a running system. coreboot allows to disable these mechanisms, making it possible to overwrite (or update) the firmware from a running system.
Usually you must use the external method once to install a retrofitted coreboot and then you can use the internal method for future updates.
There are multiple ways to update the firmware:
More details on flashrom's
External flashing is possible on many platforms, but requires disassembling the target hardware. You need to buy a flash programmer, that exposes the same interface as your flash IC (likely SPI).
Please also have a look at the mainboard-specific documentation for details.
After exposing the firmware flash IC, read the schematics and use one of the possible methods:
WARNING: Using the wrong method or accidentally using the wrong pinout might permanently damage your hardware!
WARNING: Do not rely on dots painted on flash ICs to orient the pins! Any dots painted on flash ICs may only indicate if they've been tested. Dots that appear in datasheets to indicate pin 1 correspond to some kind of physical marker, such as a drilled hole, or one side being more flat than the other.
On platforms where the flash IC is shared with other components you might want to write only a part of the flash IC. On Intel for example there are IFD, ME and GBE which don't need to be updated to install coreboot. To make flashrom only write the bios region, leaving Intel ME and Intel IFD untouched, you can use a layout file, which can be created with ifdtool and a backup of the original firmware.
ifdtool -f rom.layout backup.rom
and looks similar to:
00000000:00000fff fd 00500000:00bfffff bios 00003000:004fffff me 00001000:00002fff gbe
By specifying -l and -i flashrom writes a single region:
flashrom -l rom.layout -i bios -w coreboot.rom -p <programmer>
flashrom version 1.0 supports reading the layout from the IFD (first 4KiB of the ROM). You don't need to manually specify a layout it, but it only works under the following conditions:
flashrom --ifd -i bios -w coreboot.rom -p <programmer>
TODO explain FMAP regions, normal/fallback mechanism, flash lock mechanisms