Interface Synthesis Requirements - 2022.1 English

Vitis High-Level Synthesis User Guide (UG1399)

Document ID
Release Date
2022.1 English

To use the C/RTL co-simulation feature to verify the RTL design, at least one of the following conditions must be true:

  • Top-level function must be synthesized using an ap_ctrl_chain or ap_ctrl_hs block-level protocol
  • Design must be purely combinational
  • Top-level function must have an initiation interval of 1
  • Interfaces must be all arrays that are streaming and implemented with axis or ap_hs interface modes
    Note: The hls::stream variables are automatically implemented as ap_fifo interfaces.

If at least one of these conditions is not met, C/RTL co-simulation halts with the following message:

@E [SIM-345] Cosim only supports the following 'ap_ctrl_none' designs: (1) 
combinational designs; (2) pipelined design with task interval of 1; (3) designs with 
array streaming or hls_stream ports.
@E [SIM-4] *** C/RTL co-simulation finished: FAIL ***
Important: If the design is specified to use the block-level IO protocol ap_ctrl_none and the design contains any hls::stream variables which employ non-blocking behavior, C/RTL co-simulation is not guaranteed to complete.

If any top-level function argument is specified as an AXI4-Lite interface, the function return must also be specified as an AXI4-Lite interface.