Part 12 answers: How do we save power without losing data?
Links and interfaces spend much of their time idle, and an idle link that stays fully on burns power for nothing. Turning it off is easy; turning it off without losing a transaction, and waking it fast enough, is the protocol problem.
This part covers idle detection, link power states, break-even time, low-power handshakes, quiescing and wake signalling.
Compute the break-even time of a low-power state.
Explain why a device may deny a power-down request.
Drain an interface safely before removing its power.
Answer each in your head before opening it. If two or more feel shaky, revisit Part 11: Bring-Up and Link Management first.
Its receivers must lock to the incoming clock, align lanes and tune equalisation for the particular channel before data can be trusted.
Negotiate down to the highest speed both support, the lowest common denominator.
They give later versions room to add features that old devices ignore safely, which keeps old and new devices compatible.
# | Lesson | Level | Status |
|---|---|---|---|
12.1 | W · Working | Ready | |
12.2 | W · Working | Ready | |
12.3 | S · Senior | Ready | |
12.4 | S · Senior | Ready | |
12.5 | S · Senior | Ready | |
12.6 | W · Working | Ready | |
— | all levels | Ready | |
— | all levels | Ready |
Every lesson in this part is ready. Work through them in order: each one sets up the problem the next one solves.