Hi everyone, this is a Test Offer for an experimental PCIe bifurcation patch for the ASUS Sabertooth X79 BIOS 4801 already modified by Koekieezz.
The goal is to restore/test true x4x4x4x4 PCIe bifurcation on the Sabertooth X79, which has historically been problematic on this platform.
This work started from the modded Sabertooth X79 BIOS discussed in the existing offer thread:
I then went back to the older X79 bifurcation discussion:
and compared the relevant Sabertooth UEFI code against a Gigabyte GA-6PXSV4 BIOS where full x4x4x4x4 bifurcation is known to work.
What I found
The relevant module GUID is:
79AA6086-035A-4AD9-A89A-A6D5AA27F0E2
The Sabertooth BIOS contains two copies of this module.
In the working Gigabyte implementation, the corresponding routine generates different port-enable bitmaps:
0x0F / 0x0D / 0x07 / 0x05 / 0x01
while the Sabertooth routine had the relevant cases hard-coded to:
0x01
The value is subsequently used as a bitmask for the PCIe/IIO ports:
(bitmap >> port_index) & 1
So 0x01 effectively enables only port index 0, while 0x0F enables all four port bits.
Patch
I therefore made a very small surgical patch:
-
module copy #1:
-
+0x64C : 01 -> 0F -
+0x6E8 : 01 -> 0F
-
-
module copy #2:
-
+0x64C : 01 -> 0F -
+0x6E8 : 01 -> 0F
-
The two modified locations correspond to the IOU2 and IOU3 port bitmaps.
The FFS file checksums were recalculated accordingly.
The complete patched CAP differs from the original BIOS by only 6 bytes total:
-
4 functional
01 -> 0Fchanges -
2 updated FFS checksum bytes
No FFS sizes, FV layout, padding, capsule header, or unrelated modules were changed.
The patched image has also been checked with UEFIExtract / UEFIFind and the modified PE32 modules were verified after patching.
At this point the patch is technically consistent, but still experimentally unproven on real hardware.
I’m looking for users who can test it on a Sabertooth X79, preferably with hardware capable of exposing four downstream PCIe links, such as:
-
ASUS Hyper M.2 x16
-
passive PCIe bifurcation adapter
-
another suitable multi-device PCIe card witouth multiplexers.
The ideal result would be confirmation that the platform actually exposes 4 × PCIe x4 instead of the usual reduced configuration.
Please report both successful and unsuccessful results. A partial result such as 2/4 devices detected would also be useful.
this is an experimental Test Offer, not a claim that x4x4x4x4 has been definitively restored. Hardware testing is specifically what is still missing.
**If the patch works, we may finally have a code-level explanation and practical fix for the long-standing Sabertooth X79 x4x4x4x4 limitation**
BIOS_SABERX79_KOEKIEEZZ_x4x4x4x4_patched_TEST.zip (4.8 MB)
Edit by Fernando: Thread title shortened