GRML Linux based flash tool with flashrom, amdvbflash, and 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. Unfortunately this method creates a 1GB filesystem with limited free space, enough to store your Macs firmware and your video bios image. If you have a USB device with more capacity format it using FAT/GUID (not ExFAT!), just open the image in Finder, and copy all folders over to the new and bigger drive. GUID allows you to add OpenCore via OCLP to the EFI partition on the USB to get an emulated boot screen on Macs with PC graphics cards.
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 listed below.
Please note the most recent graphics card BIOS versions will be found on this separate repository. You will have to download the file you need separately and add it manually to the tool provided here, the folder flash -> video is the best place to save it.
You can also update amdvbflash and nvflash manually, I will not create new releases each time a new software version hits the internet.
Supported iMac models are:
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 MacPro3,1, MacPro4,1 or MacPro5,1 or even on normal PCs!
Supported graphics hardware includes all ATI/AMD and NVIDIA cards usable in Mac Intel hardware. Most recent graphics cards may need updated versions of amdvbflash or nvflash.
If your Mac has no 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. Please note v2.0.0 has folder names changed from Video to video and Firmware to firmware (good old Unix habit).
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
In case you find a more recent BIOS already on your card you can force writing an older version using
% ./amdvbflash -f -p 0 AMD/NewAMDBios.rom
Reboot after flashing the video BIOS.
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 or PC without installing another boot loader and you have read and write access from the Apple Finder or Windows desktop. GRML uses normally Linux ext2, so we have to boot strap through two stages folling this guide or the condensed description below by using the existing GRML tool. First download a new/recent version of GRML here. Recent version is named 2024.02 and it has Navi23 drivers.
Put the ISO image either into the flash folder and navigate there as usual after booting Linux or download it using ssh into the /root folder.
Now plug in another prepared USB or SD-card (FAT32/GUID) and check the /etc/vfstab file of your currently booted Linux, the last line will reveal the device where the newly plugged in device can be accessed. Usually I name the new device differently like NEWFLASH.
Finally start the process by entering the command line below (assuming /dev/sdc2 is the device of choice):
% grml2usb --bootoptions="keyboard=de ssh=flash persistence" --skip-bootflag grml64-full_2021.07.iso /dev/sdc2
Just to confuse you all, the keyboard=de sets keyboard layout to German, which I usually have around here. You can either delete the keyboard setting or adapt it to your local needs. The ssh=flash sets the ssh password to flash, the persistence flag makes the USB writable after booted into Linux to save PC/Mac firmware or graphics card firmware aka vBIOS files.
Finally you can mount the USB on your macOS system and add copy over the flash folder from the old version or create a new one to have a fresh start. All releases here have a prepared flash folder with some binaries and other files.
GRML is a packaged Linux distribution based on Debian. Debian license rules can be found on the Debian 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.