4 ms·
It's interesting to hear that the 3DFx adjusted the clock that way. Coincidentally, I was just reading about similar clock adjustment in the Pentium II and 4.
by kens 6y ago
It's interesting to hear that the 3DFx adjusted the clock that way. Coincidentally, I was just reading about similar clock adjustment in the Pentium II and 4. They had "adaptive deskewing", where a phase comparator would adjust the clock delay as needed. It sounds like 3DFx did the adjustment at startup, but the Pentium did it during use so it could compensate for temperature drift. The Itanium 2 had similar deskewing, except the value was set during manufacturing by blowing fuses.
Source: "CMOS VLSI Design", page 806.
- ChuckNorris89 6y agoIIRC Intel does similar but way more advanced automatic deskewing black magic in the thunderbolt controllers. That's how they can carry high speed PCIe signals so effortlessly across your average copper cable(it was originally supposed to be optical).
- p_l 6y agoThat's somewhat standard part of transceivers with addition that PCI-E lower layers implement forced skew themselves - even on the motherboard. While I don't exactly know the case with Thunderbolt, "normal" Display Port uses PCI-E physical layer, just unidirectional and with different protocol on top. On networking equipment, the necessary signal corrections are part of why (other than DRM) it's more expensive to use full transceivers that accept cables, vs. fixed-length cables with fixed transceivers vs. direct-attach cables which have minimal logic for signal quality.