Oculink board and shutdown problems

Kinda odd question here. Requires a little background to explain why I’m doing this.

My main PC is microATX, and I generally have two pci-e cards attached - gpu + 10gbit nic. I love, love, love this case. It’s all mesh, and has the PSU up front, keeping free space on the bottom to attach fans to shoot cool air directly into the gpu intake fans.

I finally pulled the trigger on a platform upgrade from AM4->AM5. Since I often do pretty large file transfers to an external SSD, I decided to go x870 (for the USB4 ports).

Unfortunately, there are no microATX x870 (or even x670) motherboards in production anywhere. So I went mini-ITX instead.

Since those boards all have just one pci-e slot, I decided to frankenstein my own 2nd internal pcie-slot with a cablecc oculink pci-e host adapter, and cannibalized one of the m.2 slots on the motherboard for use with an m.2->oculink adapter.

This setup seems to work great - I get full 10gbit ethernet speeds, and the OS is none the wiser that the card isn’t attached to a normal motherboard slot.

Well I lied a little - it works great UNTIL I HIT THE POWER BUTTON. Then, on shutdown, all hell breaks loose. Once the OS tells the motherboard to power down, it looks like the PSU is unable to (since the cablecc card has a little power switch in the on position, and shares the 24-pin PSU power via. a splitter). This inability to comply with the shutdown signal results in all the fans (CPU, chassis, and GPU) spinning like mad until I physically disconnect the PSU power cable.

The case has the PSU up front, with an extender cable on the back panel for the wall socket power cable, so I don’t even have physical access to the PSU power switch.

I’m starting to fear my only option is to put the system on its own AC splitter and just hit the red switch every time I need to shut down.

Unless the hive mind here can come up with a better solution???

I would suggest following:
I wouldn‘t splice power of the PSU and ditch the adapter.

Couldn’t you give the occulink receptor (I assume it is a occulink to PCIe bridge) its own powersupply (can be a small SFF PSU or a pico PSU if it just provides the pcie 75W) and then set the occulink receptor power pin / switch to auto (= turn on if occulink source gets power)?
Your m.2 > occulink adapter has to support it, but some can broadcast their state ( am I powered on) to the occulink receptor and it will power on (or off).

Solution 2:
Would be a smart powerstrip which switches off if power consumption of your PC drops. This might not work if the drop isn’t sufficient while the PC is in panic mode or might lead to unwanted shutdowns if your device is already a low power PC or goes to standby. We had a few 1 port solutions in my former workplace.



Thanks for the reply - certainly better ideas than my current approach! I’ll research miniature power supplies, see if I can find a way to attach them somewhere to the case. One other alternative I considered early on - I did see some other oculink->pci-e host boards using sata power instead of 24-pin, but because of the available space at the bottom of my case, those were too wide and wouldn’t fit to provide a ‘normal’ positioned pci-e slot. I suppose it’s not really necessary that the nic be in a normal card position - I could just have it hanging free a little farther in the case (and just string the rj45 cable into the case through an empty slot hole). I suppose sata is fine for the draw my nic is likely to impose (although the rated sata max of 54W is short of the 75w spec power that pci-e slots are supposed to provide - a nic will only be in the 5W range anyways).

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I just realized the easiest solution - I can keep my current setup with one tiny change: after the 24-pin split, on the oculink board side, I can just cut the wire for pin #16 (PS_ON), ensuring that the oculink board never pulls it to ground. This will inhibit the oculink board from sending a power-on signal to the PSU, leaving the motherboard as the only device providing it.

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