time card

For LTX 2023, I built this:

This build centers around the Time Card mini. Typically you'd install this PCI Express card inside another computer, but in my case, I just wanted to power the board in a semi-portable way, and so I plugged it into a CM4 IO Board.

The Time Card mini is a PCIe-based carrier board for the Raspberry Pi Compute Module 4, and by itself, it allows you to install a CM4 into a PC, and access the CM4's serial console via PCIe.

But the real power comes in 'sandwich' boards:

I've been following the issue CM4 is missing IEEE1588-2008 support through BCM54210PE since I heard about IEEE1588-2008 support on the Compute Module 4 last year.

Apparently the little NIC included on every Compute Module 4—the BCM54210PE, which is different than the NIC on the Pi 4 model B (a BCM54213PE)—includes support for a feature called PTP, or Precision Time Protocol.

Ahmad Byagowi, the project lead for Open Compute Project's Time Appliance, reached out to me a couple weeks ago and asked if I'd be willing to test the new Time Card Facebook had announced in mid-August on a Raspberry Pi Compute Module 4. Since I have a sort of obsession with plugging anything and everything into a Pi to see what works and what doesn't, I took him up on the offer.

The official specs had PCI Express Gen 3 on a x4 slot as a requirement, but it seems the Gen 3 designation is a little loose—the card and its driver should work fine on an older Gen 2 bus—like the one the Raspberry Pi Compute Module 4 exposes if you use the official IO Board:

The slot is x1, but you can plug in any width card using an adapter like this one or by hacking an open end into it with a razor saw or dremel tool.