Part 4 answers: How much may I send before I hear back?
A handshake works when the receiver can answer within a cycle. Over a long, pipelined path the answer arrives late, and everything sent in the meantime needs somewhere to land. Flow control decides how much the sender may send before it hears back.
This part covers stop/go, credits, windows and rate limits; how to size buffers from the round trip; credit classes and their bugs; hop-by-hop versus end-to-end control; lossless versus lossy networks; switching modes; head-of-line blocking; and a decision guide.
Explain credit-based flow control and its conservation invariant.
Size a receiver buffer from bandwidth and round-trip time.
Choose between valid/ready, on/off and credits for a given link.
Answer each in your head before opening it. If two or more feel shaky, revisit Part 3: Handshakes first.
On a rising clock edge where valid and ready are both high. Both sides see the same two signals, so they always agree on whether the data moved.
If the sender waited for ready while the receiver waited for valid, neither would ever assert its signal: a deadlock.
The sender learns about a stall one cycle late, so one more word can arrive after ready falls. The second entry catches it without dropping it.
# | Lesson | Level | Status |
|---|---|---|---|
4.1 | F · Foundation | Ready | |
4.2 | W · Working | Ready | |
4.3 | F · Foundation | Ready | |
4.4 | W · Working | Ready | |
4.5 | S · Senior | Ready | |
4.6 | S · Senior | Ready | |
4.7 | S · Senior | Ready | |
4.8 | S · Senior | Ready | |
4.9 | W · Working | Ready | |
4.10 | S · Senior | Ready | |
4.11 | S · Senior | Ready | |
4.12 | W · Working | Ready | |
4.13 | S · Senior | Ready | |
4.14 | W · Working | Ready | |
4.15 | P · Principal | 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.
This course teaches why protocols are designed the way they are. These lessons show how to build or sign off the same ideas, so this part links to them instead of repeating them.