Generating VCD with Select Signals - 2025.2 English - UG1076

When you provide the --dump-vcd option, the aiesimulator generates all signals in the VCD file (except CLK,STREAM_SWITCH). This generation can slow down simulation. Alternatively, using options to generate select signals associated with specific modules can improve simulation speed.

To debug a design, it is recommended that you run aiesimulator with --dump-vcd to generate all the signals. After the issue is narrowed down, run the aiesimulator with options to generate a subset of VCD signals. To do this, pass aiesimulator with specific options through an options text file. The options provided in the text file determine the selected signals.

To enable VCD generation for specific modules, select the module type in a text file, and pass the file an input to the aiesimulator command line. The contents of the file merge into the generated aie_simulator/aiesim_options.txt. The usage of this file in the HW emulation flow remains the same. Options passed to the aiesimulator command line have higher precedence over the same options provided in the options file.

 aiesimulator --options-file=<user_aiesim_options.txt> --dump-vcd=<file_name>

See the list of selections below. By default, all modules except CLK and STREAM_SWITCH are set to true. Set the option to false to turn off modules.

Row/Column Selection

AIE_DUMP_VCD_ROW=(<row start index>,<row end index>),( <row start index>,<row end_index>)...
AIE_DUMP_VCD_COL=(<column start index>,<column end index>),( <column start index>,<column end_index>)...

Row

Use AIE_DUMP_VCD_ROW to generate VCD data for all the active cores in the selected row. You must specify absolute coordinates that consider the AI Engine interface row as row 0.

Example: To generate VCD data for active cores present between rows 1 to 4, specify it as AIE_DUMP_VCD_ROW=(2,5) in the options.txt file.

Column

Use AIE_DUMP_VCD_COL to generate VCD data for all the active cores present in the selected column.

Example: To generate VCD data for active cores present between columns 23 to 26, specify it as AIE_DUMP_VCD_COL=(23,26) in the options.txt file.

Time interval

Use AIE_DUMP_VCD_INTERVAL to generate VCD data for a given time period. The generated VCD file contains data related to all active cores for the selected time period. Only one time period specification is supported.

Note: End time -1 means end of simulation.

Example: To generate VCD data from 600 ns to 700 ns, use AIE_DUMP_VCD_INTERVAL=(600,701).

Tile Type Selection

AIE_DUMP_VCD_CORE=true/false   
AIE_DUMP_VCD_SHIM=true/false 
AIE_DUMP_VCD_MEM=true/false (valid for AIEngine ML designs only)

Core

Use AIE_DUMP_VCD_CORE to generate VCD data with signals associated with processor modules, programs and data memory.

Shim

Use AIE_DUMP_VCD_SHIM to generate VCD data with signals associated with all AI Engine interface tiles.

Mem

Use AIE_DUMP_VCD_MEM to generate VCD data with signals associated with all mem tiles. This option valid for AI Engine-ML designs only.

Tile Submodule Selection

To output VCD data around tile submodules, select the tile type category described above.

AIE_DUMP_VCD_IO=true/false
AIE_DUMP_VCD_DMA=true/false
AIE_DUMP_VCD_STREAM_SWITCH=true/false
AIE_DUMP_VCD_CLK=true/false

This categorization of module signals directly relates to the category of the information shown on the Analysis View of the Vitis Unified IDE:

I/O

Use AIE_DUMP_VCD_IO to generate VCD data with signals associated with AI Engine kernel input/output, locks, and stalls. To generate this VCD data you must specify this option with any one of the tile type options: AIE_DUMP_VCD_CORE, AIE_DUMP_VCD_SHIM, or AIE_DUMP_VCD_MEM.

DMA

Use AIE_DUMP_VCD_DMA to generate VCD data with signals associated with DMA transfers, and locks. To generate this VCD, specify this option with any one of the tile type options: AIE_DUMP_VCD_CORE, or AIE_DUMP_VCD_MEM.

Stream Switch

Use AIE_DUMP_VCD_STREAM_SWITCH to generate VCD data with signals associated with all the streams on the stream switch boundary. To generate this VCD data, specify this option with any one of the tile type options: AIE_DUMP_VCD_CORE, AIE_DUMP_VCD_SHIM, or AIE_DUMP_VCD_MEM.

Clock

Use AIE_DUMP_VCD_CLK to generate VCD data for the clock signal.