Exporting simulation data to a txt file using tcl commands in Modelsim

Jul 14, 2025#FPGA0

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The document provides a Tcl command procedure for exporting simulation data from Modelsim to a text file. The procedure, named `write_sim_data`, takes parameters such as the environment path, variable names, radix, clock cycle, and output file name. It opens the specified file, samples data at intervals defined by the clock cycle, retrieves the simulation data, writes it to the file, and then closes the file. An example usage of the procedure is also included, demonstrating how to export specific variables to a text file.

Refer to the CSDN blog below

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Tcl Commands#

proc write_sim_data {env name radix cycle file} {
    set fid [open $file w]
    for {set i 0} {$i <= $::now} {incr i [expr $cycle * 1000]} {
        set str [exa -env $env -radix $radix -time ${i}ps {*}$name]
        puts $fid $str
    }
    close $fid 
}

Line1: Defines a procedure named write_sim_data with the parameter list: {env name radix cycle file}

env: Specifies the path to the object name. For example, top_tb/top_u
name: The list of variables to be exported. For example, {I_reset_n R_data_cnt}
radix: Number base. Options: ascii, binary, decimal, hexadecimal, unsigned, etc.
cycle: Clock cycle, in ns
file: Output file. For example, ./1.txt
Line2: Opens a document and returns the file descriptor
Line3: Samples and outputs data at clock cycle intervals from 0 to the end of simulation time
Line4: Obtains specific data
Line5: Writes data to the file
Line7: Closes the file

Example:

write_sim_data sim:/top_tb/u_top_wrapper/top_i/RS_Enc_0 {RS_Out Trigger} unsigned 1000 data.txt