AXI BFM(bus function model)

• standard protocol
• write phase (fork events)
• write address phase
• collect transactions when AXI_AWVALID and AXI_AWREADY
• write data phase
• collect transactions when AXI_WVALID and AXI_WREADY
• write response phase
• collect transactions when AXI_BVALID and AXI_BREADY
• the valid transaction should have the same ID at address, data, response 
• 
  
• read phase(fork events)
• read address phase
• collect transactions when AXI_ARVALID and AXI_ARREADY
• read data phase
• collect transactions when AXI_RVALID and AXI_RREADY
• the valid transaction should have the same ID at address, data
• extend protocol
• qos
• user
• region
• lock
• cache
• strb
• https://github.com/funningboy/axi-bfm