Term | Meaning | Taught in |
|---|---|---|
4 KB rule | An AXI burst must not cross a 4 KB boundary, so a master or bridge splits any longer burst at the boundary. | |
APB | The simple peripheral bus: a setup phase, an access phase, PREADY to stretch the access. NanoSoC uses the APB3 style, which has PSLVERR but no PSTRB and no PPROT. | |
Arbitration | Choosing which master gets a contended slave. NanoSoC uses round robin per slave with one idle cycle when the winner changes. | |
AXI4 | The public burst-based bus with five independent channels (AW, W, B, AR, R) each with a valid and ready handshake. NanoSoC uses it at 32 bits with INCR bursts of up to 16 beats. | |
Beat | One data transfer on a channel in one clock where valid and ready are both high. A burst is a series of beats. | |
Bottleneck link | The link in a path with the lowest sustained rate. It sets the throughput of the whole path, so raising any other link changes nothing. | |
Bridge | A block that converts between protocols or clocks, such as the AXI to APB bridge. Each bridge adds latency and lowers throughput. | |
Burst efficiency | The fraction of cycles that carry data: with L beats and one bubble per burst it is L/(L+1), which is 94.1% at L = 16. | |
Crossbar | An interconnect with a separate path per master and slave pair, so transfers to different slaves proceed together and only a shared slave needs arbitration. | |
Deadlock | A cycle of masters and slaves each waiting for another, so nothing moves. At SoC level it comes from dependencies the interconnect cannot see. | |
Firewall (address range) | A check in front of a slave that admits or refuses accesses by address range and master identity, beyond the secure bit. | |
ID and outstanding transactions | AXI tags each request with an ID; responses with the same ID return in order. Write data has no ID in AXI4. Outstanding means issued but not yet answered. | |
Network on chip (NoC) | An interconnect that sends packets through routers instead of wiring a crossbar. It pays off when many blocks and long wires make a crossbar too large. | |
Peak and sustained bandwidth | Peak is width times frequency: 4 bytes x 96 MHz = 384.0 MB/s. Sustained is what survives bubbles, arbitration and bridges: 361.4 MB/s at burst 16. | |
Quality of service (QoS) | Per-master priority or bandwidth rules that bound how much a contended slave favours one master over another. | |
Starvation | A master that is never granted because others always win. Round robin bounds the wait; fixed priority does not. |
Back to the Glossary for the other groups and the look-alike terms.