Multiple AXI-Lite interfaces/VitisNetP4 instances in one user box

[DavidoTek]

Hi everyone,

we're currently working on a plugin for the 250MHz user box that includes two VitisNetP4 instances and a custom PIFO (Push-In First-Out) queue in between. Our P4 implementation is based on https://github.com/OCT-FPGA/P4Framework.

When there is a single VitisNetP4 instance, it is directly connected to the AXI-Lite interface of the user box and it can be addressed at address 0x100000 from the host.
How can multiple AXI-Lite slaves be connected to the AXI-Lite interface? We thought about the following approaches:

1. Add an AXI-Lite switch/demultiplexer to the user box (e.g., https://github.com/pulp-platform/axi/blob/master/src/axi_lite_demux.sv) or add an additional AXI crossbar IP
2. Somehow modify the AXI crossbar in the glue logic of the user box to handle additional AXI-Lite slaves. We noticed that there is at least one AXI-Lite interface per physical function/interface and increasing NUM_INTF increases the number of AXI-Lite interfaces, but I think it makes the most sense to keep NUM_INTF at 1 if only one is used.

What approaches can you recommend, do you have any further ideas? Can someone provide us with an example that shows similar behavior?

Thanks!

---

Update: We decided to focus on modifying the AXI crossbar in the user box's glue logic because it does not involve any additional components.

The following changes yielded the expected result:

1. Add an additional AXI-Lite interface to the p2p_250mhz module (p2p_250mhz.sv)
2. Adjust the AXI-Lite interfaces in box_250mhz_address_map_inst.vh and user_plugin_250mhz_inst.vh accordingly
3. Also add the new interface in box_250mhz_address_map.v. C_NUM_SLAVES needs to be increased by 1, new ..._INDEX and ..._ADDR parameters need to be added and new connections/assignments are required. Example:
   • C_NUM_SLAVES = 3
   • C_P2P_ONE_INDEX = 0 , C_P2P_TWO_INDEX = 1
   • C_P2P_ONE_BASE_ADDR = 32'h0 , C_P2P_TWO_BASE_ADDR = 32h10000`
   • assign axil_p2p_one_awaddr = axil_awaddr[C_P2P_ONE_INDEX*32 +: 32] - C_P2P_ONE_BASE_ADDR
   • assign m_axil_p2p_one_awvalid = axil_awvalid[C_P2P_ONE_INDEX]
   • assign axil_p2p_two_awaddr = axil_awaddr[C_P2P_TWO_INDEX*32 +: 32] - C_P2P_TWO_BASE_ADDR
   • assign m_axil_p2p_two_awvalid = axil_awvalid[C_P2P_TWO_INDEX]
   • ...
4. The new interface is configured in box_250mhz_axi_crossbar.tcl: Increase CONFIG.NUM_MI by 1 and add CONFIG.Mmm_Aaa_BASE_ADDR and CONFIG.Mmm_Aaa_ADDR_WIDTH for the new interface (see PG059: AXI Interconnect v2 , page 107)
   • CONFIG.NUM_MI {3}
   • CONFIG.M00_A00_ADDR_WIDTH {16}
   • CONFIG.M00_A00_BASE_ADDR {0x0000000000000000}
   • CONFIG.M01_A00_ADDR_WIDTH {16}
   • CONFIG.M01_A00_BASE_ADDR {0x0000000000010000}

Each of the VitisNetP4 instances needs to be connected to one of the two AXI-Lite connections. The host driver "c-driver" code needs to be adjusted accordingly: UserCtxPtrOne->VitisNetP4Address = 0x100000 and UserCtxPtrTwo->VitisNetP4Address = 0x110000