4 ms·
How does this stay compatible with PCIe generation 5 and earlier while the encoding changes from interleaved digital (128b/130b from 3.0 to 5.0) in to PAM?
by anticensor 5y ago
How does this stay compatible with PCIe generation 5 and earlier while the encoding changes from interleaved digital (128b/130b from 3.0 to 5.0) in to PAM?
- ahartmetz 5y agoPresumably by falling back to the lowest version supported by both sides, with negotiation done in 1.0 encoding or so. It's a standard technique. Also note that PCIe is point-to-point so no downgrading for devices just idling on the same bus.
- Tuna-Fish 5y agoWhen two PCIe devices are connected to each other, they don't instantly start talking PCIe, they start in a complex autonegotiation mode [0], where they find out the width of the link, the maximum protocol version that each side support, and the maximum speed that the connection between them can support. [0]: PCIe LTSSM. I sadly cannot link the spec here because it requires registration but have the diagram someone kindly ripped for SO: https://i.stack.imgur.com/QYyCM.png https://i.stack.imgur.com/QYyCM.png
- marcan_42 5y agoThe same way all the other generations stayed compatible; the encoding already changed from 8b10b to 128b/130b in the past. There's a negotiation protocol involved (LTSSM).
- baybal2 5y agoLine code is not going anywhere, it just changes to 242/256