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Signal Description
AXI signal names are easiest to read by channel prefix. The local specification’s Appendix B1 is the complete channel signal reference. This section summarizes the main channel groups once, so later sections can refer to the signals by behavior instead of re-listing them.
Write channels
| Channel | Prefix | Direction | Common signals | Optional signals |
|---|---|---|---|---|
| Write request | AW | Manager to Subordinate | AWVALID, AWREADY, AWID, AWADDR, AWLEN, AWSIZE, AWBURST, AWLOCK, AWCACHE, AWPROT, AWQOS, AWDOMAIN, AWSNOOP, AWUSER | Credited transport signals, AWREGION, AWPAS, AWMECID, AWNSAID, AWSUBSYSID, AWATOP, AWMPAM, AWIDUNQ, AWCMO, AWTAGOP, AWACT |
| Write data | W | Manager to Subordinate | WVALID, WREADY, WDATA, WSTRB, WLAST, WUSER | Credited transport signals, WTAG, WTAGUPDATE, WPOISON |
| Write response | B | Subordinate to Manager | BVALID, BREADY, BID, BRESP, BUSER | Credited transport signals, BCOMP, BPERSIST, BTAGMATCH, BBUSY |
Read channels
| Channel | Prefix | Direction | Common signals | Optional signals |
|---|---|---|---|---|
| Read request | AR | Manager to Subordinate | ARVALID, ARREADY, ARID, ARADDR, ARLEN, ARSIZE, ARBURST, ARLOCK, ARCACHE, ARPROT, ARQOS, ARDOMAIN, ARSNOOP, ARUSER | Credited transport signals, ARREGION, ARPAS, ARMECID, ARNSAID, ARSUBSYSID, ARMPAM, ARCHUNKEN, ARIDUNQ, ARTAGOP, ARACT |
| Read data | R | Subordinate to Manager | RVALID, RREADY, RID, RDATA, RRESP, RLAST, RUSER | Credited transport signals, RTAG, RPOISON, RCHUNKV, RCHUNKNUM, RCHUNKSTRB, RBUSY |
Snoop channels
| Channel | Prefix | Direction | Common signals | Optional signals |
|---|---|---|---|---|
| Snoop request | AC | Subordinate to Manager | ACVALID, ACREADY, ACADDR | Credited transport signals, ACVMIDEXT, ACTRACE |
| Snoop response | CR | Manager to Subordinate | CRVALID, CRREADY | Credited transport signals, CRTRACE |
In this specification, snoop channels are used for DVM messages. Designs that do not support DVM omit these channels.
Interface-level signals
| Group | Signals |
|---|---|
| Clock/reset | ACLK, ARESETn. |
| Wakeup | AWAKEUP, ACWAKEUP. |
| Credit control | ACTIVATEREQ, ACTIVATEACK, ASKSTOP, and DVM-channel variants. |
| Coherency connection | SYSCOREQ, SYSCOACK. |
| Static control | BROADCASTATOMIC, BROADCASTSHAREABLE, BROADCASTCACHEMAINT, BROADCASTCMOPOPA, BROADCASTPERSIST, BROADCASTSTORAGE. |
The short rule:
AW, W, and AR usually move away from the Manager; B and R return toward the Manager; AC moves DVM requests toward a Manager; and CR returns the DVM response.
AXI Protocol