Arbitration Modes
The AXI Interconnect core includes arbiter engines that grant the request to an AXI master when more than one AXI master issues a request. The AXI Interconnect supports three types of arbitration modes.
Fixed Priority
In this mode, the arbiter always prioritizes the most significant bit (MSB) ports as indicated by the bits shown in bold in the following example. Lower priority ports suffer from starvation.
| Request | 11100000 | 11100000 | 11100000 | 1110010 | 00001011 | 00000000 | 00001111 | 11111111 |
| Grant | 10000000 | 10000000 | 10000000 | 10000000 | 00001000 | 00000000 | 00001000 | 10000000 |
Round Robin 1
The arbitration starts from the MSB port. When more than two transaction requests are issued at the same time, the arbiter grants the request to the port sitting on the right-hand side nearest to the previously served port.
Example:
| Request | 11100000 | 11100000 | 11100000 | 1110010 | 00001011 | 00000000 | 00001111 | 11111111 |
| Grant | 10000000 | 01000000 | 00100000 | 00000010 | 00000001 | 00000000 | 00001000 | 00000100 |
Round Robin 2
The arbitration starts from the MSB port. The arbitration goes through all connected master ports sequentially with a counter. When there is no request from the assigned master, the arbiter grants the port sitting on the right-hand side nearest to the assigned port. There are no counter increments when there are no requests.
Example:
| Request | 11100000 | 11100000 | 11100000 | 1110010 | 00001011 | 00000000 | 00001111 | 11111111 |
| Counter | 7 | 6 | 5 | 4 | 3 | 3 | 2 | 1 |
| Grant | 10000000 | 01000000 | 00100000 | 00000010 | 00001000 | 00000000 | 00000100 | 00000010 |