It seems to show CFG[6:5] (pins U40, U39 respectively) are responsible for setting the bifurcation mode. In the case of this motherboard, CFG5 (U39) is tied to VSS, which leaves only 2x8 and 1x8 and 2x4 bifurcation modes according to page 89 of the datasheet.
CFG6, however is not mapped to either VSS or VCC, and should therefore be configurable somewhere on the board.
I imagine one of the GPIO pins (72,57,32,28,27,15,8) could be responsible for that particular setting. But that could also be assigned to a different IC somewhere else on the board.
CFG6 is not mapped to any controllable pin. By default it is set to 1 (what happens when its unterminated)
CFG6 is also connected to R278 (the other side of which is connected to the +3VDC of the coin cell), R83 (the other side of which is connected to VSS), and JITPT1 Pin 35 (located on the back of the motherboard). There are no other connections I could find to CFG6
Therefore: To enable x4x4 bifurcation, a soldering iron is required and a 0 ohm resistor or solder blob on R83 will enable it. Any PCIe x8 device will run at x4 speeds if placed in CPU Slot 5.
Just out of curiousity: These boards have afaik max 3 PCIe slots:
PCIe Gen 3
2 slots connected to the CPU (16 lanes), configured 2 x 8
8 lanes in a x16 connector, but probably just 8 lanes electrically connected,
8 lanes in a x8 connector
PCIe Gen 2
1 slot connected to the PCH
4 lanes in a x8 connector
So in my understanding the only thing you might achieve is to reduce on of the Gen 3 x8 slots to x4? What is it I’m missing here?
What you gain is the ability to put two x4 devices (like two nvme drives) into that single middle pcie 3.0 x8 slot with a passive bifurcation card like this one:
But if the M.2 Card has its own BIF chipset, it will manage the lanes itself to her own devices, without the need of motherboard control lanes… the card will manage the required lanes to each of the disks…i dont see in this case what is the need of motherboard mod BIF.
I dont see any signs of a BIF chip on that adapter (Can you identify for us the controller?), in that case yes mod is required to a motherboard lacking such function.
Sorry if my point of view is wrong here…just my opinion.
I agree, the correct way to do this isn’t to take an iron to your motherboard, but to instead get a card with a PLX chip on it.
The advantage is there is no BIF chip on that adapter, its entirely passive (all the components are power regulators)
Your point of view isn’t wrong at all. I’m just offering a solution for cheaper (this bifurcation card is significantly cheaper than the PLX based cards).
