GRML Linux based flash tool with flashrom, amdvbflash, nvflash
Download disk image (check releases on this page) and restore it using the Balena Etcher tool onto an USB or SD device of at least 1 GB size.
The purpose of this tool is to use amdvbflash or nvflash to read existing or write new Video BIOS versions to graphics adapters or to save and modify (Apple iMac) firmware using flashrom and UEFIPatch to enable EFI boot screen support for Apple iMac models
iMac9,1 early 2009 24 inch (2,93GHz and 3,06GHz models, only)
iMac10,1 late 2009 21.5 inch
iMac10,1 late 2009 27 inch
iMac11,1 late 2009
iMac11,2 and iMac11,3 mid 2010
iMac12,1 and iMac12,2 mid 2011
Of course this tool can be used on any other Intel based system like MacPro4,1 or MacPro5,1!
If your Mac has not EFI capable graphics card installed you should simply disconnect all other drives from all connectors. On power on the Mac will scan the USB bus and find and boot the prepared Linux USB.
In case you have a black screen scenario with a non working graphics card detach all bootable disk devices, attach your iMac via ethernet directly to a router providing a DHCP service and force booting form the USB tool. Check your router for the IP address (e.g. 192.168.1.20) provided to your iMac and access the Linux distribution remotly from another PC, Mac, iPad - literally any device running an SSH client can be used. Default password of user root is flash. Access is possible through (replace IP with your address)
% ssh root@IP
The tool supports persistence, i.e. dumps from your BIOS or video BIOS can be saved on the USB device in the particualar working directory as described below.
After booting configure the local keyboard and check for the working directory using the lsblk command.
% lsblk
/lib/live/mount/persistence/sda
Note this working folder may change on different systems and on the same system on reboot. Run lsblk each time again!
To use the video flashing tools change working directory to:
% cd /lib/live/mount/persistence/sda/flash/Video
AMD card users can run the locally included amdvbflash software like this to save the existing vBIOS named OldBios.rom into the Backups folder
% ./amdvbflash -s 0 Backups/OldAMDBios.rom
Flashing a new video BIOS stored in file NewAMDBIOS.rom from folder AMD
% ./amdvbflash -p 0 AMD/NewAMDBios.rom
Saving the original version to the Backups folder
./nvflash --save Backups/OldNVBios.rom
and for flashing/writing a new video BIOS NewNVBIOS.romfrom folder NVIDIA
% ./nvflash --protectoff
% ./nvflash -6 NVIDIA/NewNVBIOS.rom
% ./nvflash --verify NVIDIA/NewNVBIOS.rom
Reboot after flashing the video BIOS.
To use the iMac/Mac BIOS flashing tools change working directory to:
% cd /lib/live/mount/persistence/sda/flash/Firmware
and
% flashrom --programmer internal -r my_firmware.bin
The resulting file my_firmware.bin has a size of 4MB until 2010 and 8MB with 2011 iMac models. Early 2009 systems have no write protections and you can write back a modified versions of the firmware easily using:
% flashrom --programmer internal -w my_modified_firmware.bin
Your saved video BIOS files can be found on the USB (Windows FAT32 format) under flash -> Video -> Backups assuming your have used the linux terminal commands as described above. Firmware files can be found in flash -> Firmware.
If you plan to write a new AMD video BIOS to your card just copy the new image into the flash -> Video -> AMD in advance.
The tool uses FAT32 to achieve double compability. It can be booted on any Mac without installing another boot loader and you have read and write access from the Apple Finder. GRML uses normally Linux ext2, so we have to boot strap through two stages folling this guide by using the existing GRML tool. Download a new version of GRML here. Upcoming version will be 2022.11.
GRML is a packaged Linux distribution based on Debian. Debian license rules can be obtained the project page.
Please look up the license rules of the mainly used software like Flashrom, amdvbflash and nvflash.
Original version has been created by xanderon on MacRumors.
If you want to support the AMD (i)Mac vBIOS development donations are greatly appreciated.