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Implementing a Spectrum Display Component in MATLAB®

MODSIMSPECDISP shows how MATLAB® can be used to implement a VHDL component that is used to display the spectrum of a signal from a VHDL project in ModelSim®. This example compiles a VHDL source containing a frequency hopping sine wave feeding a lowpass filter and defines a spectrum display component in MATLAB. The MATLAB component buffers its inputs into frames of 128 samples and displays the spectra of the unfiltered and filtered signals as the simulation is running. This example requires a temporary working directory to generate a working ModelSim VHDL project. After creating the VHDL project, this example starts ModelSim (this requires access to ModelSim from the command line). This example uses shared memory to complete the link and therefore requires ModelSim to be on the same computer as MATLAB. Once the project is compiled, the simulation can be run from within ModelSim.

Specify Files to be Used

The file sine_waves.vhdsine_waves.vhd contains the source signal designed in VHDL.

The file lowpass_filter.vhdlowpass_filter.vhd contains the lowpass filter designed in MATLAB and generated with Filter Design HDL Coder™.

The file spec_display.vhdspec_display.vhd contains the MATLAB component that we are modeling. It contains an entity with an empty architecture. The matlabcp command checks the VHDL inputs of the instance created from this entity.

The file specdisp_top.vhdspecdisp_top.vhd contains the top-level wiring between the source, lowpass filter, and the MATLAB component.

you can also define variables "UsrTclCmds" and "RunMode" with tcl commands and Modelsim's runmode. Examples:

UsrTclCmds = {'run 100000'}; RunMode = 'Batch' or 'CLI' or 'GUI';

srcfile1 = fullfile(matlabroot,'toolbox','edalink','extensions','modelsim','modelsimdemos',...
    'vhdl','specdisp','sine_waves.vhd');
srcfile2 = fullfile(matlabroot,'toolbox','edalink','extensions','modelsim','modelsimdemos',...
    'vhdl','specdisp','lowpass_filter.vhd');
srcfile3 = fullfile(matlabroot,'toolbox','edalink','extensions','modelsim','modelsimdemos',...
    'vhdl','specdisp','spec_display.vhd');
srcfile4 = fullfile(matlabroot,'toolbox','edalink','extensions','modelsim','modelsimdemos',...
    'vhdl','specdisp','specdisp_top.vhd');

ModelSim uses UNIX® style directory format which uses forward slashes ("/") instead of backslashes ("\").

unixsrcfile1 = ['"' strrep(srcfile1,'\','/') '"'];
unixsrcfile2 = ['"' strrep(srcfile2,'\','/') '"'];
unixsrcfile3 = ['"' strrep(srcfile3,'\','/') '"'];
unixsrcfile4 = ['"' strrep(srcfile4,'\','/') '"'];

Create Project Directory

We create a temporary working directory in which the project will be generated.

if ispc
    projdir = tempdir;
else
    projdir = tempname;
end
warnstatus = warning('off','MATLAB:MKDIR:DirectoryExists');
mkdir(projdir);
warning(warnstatus);
unixprojdir =  strrep(projdir,'\','/');

Start the MATLAB Server

We first start the MATLAB server, hdldaemon, such that it uses shared memory communication. We first check if the server is already running using shared memory. If hdldaemon is not running, it is started. Or, if it is running using TCP/IP socket communication, it is shut down and restarted using shared memory communication.

dstatus = hdldaemon('status');
if isempty(dstatus)
    % hdldaemon is not running
    % start it - default is shared memory communication
    dstatus = hdldaemon;
elseif strcmp(dstatus.comm,'shared memory')
    % hdldaemon is already running with shared memory
elseif strcmp(dstatus.comm,'sockets')
    % hdldaemon is running with socket communication
    % shut it down and restart it
    disp('Shutting down HDLDaemon to restart it with shared memory');
    hdldaemon('kill');
    dstatus = hdldaemon;
else
    error('unexpected return value from hdldaemon(''status'')');
end
HDLDaemon is NOT running
HDLDaemon shared memory server is running with 0 connections

Specify Tcl Commands

Next we specify the Tcl commands to execute in ModelSim before the simulation is run.

tclcmd = {};

The cd command changes to the temporary working directory.

tclcmd = [tclcmd, ['cd ',unixprojdir]];

The vlib command creates the design library work.

tclcmd = [tclcmd, 'vlib work'];

The vcom command compiles the VHDL file. The -performdefaultbinding option enables default bindings in the event that they have been disabled in the modelsim.ini file.

tclcmd = [tclcmd, ['vcom -performdefaultbinding ' unixsrcfile1],...
                  ['vcom -performdefaultbinding ' unixsrcfile2],...
                  ['vcom -performdefaultbinding ' unixsrcfile3],...
                  ['vcom -performdefaultbinding ' unixsrcfile4]];

The vsimmatlab command, a variant of the ModelSim vsim command, loads an instance of the VHDL entity for cosimulation with MATLAB. This command is a HDL Verifier™ extension to the ModelSim command set.

tclcmd = [tclcmd, 'vsimmatlab work.specdisp_top'];

The matlabcp command initiates a MATLAB component for the loaded instance of entity spec_display. This command is a HDL Verifier extension to the ModelSim command set. The -mfunc option specifies specdisplay.mspecdisplay.m will be used to implement this component.

tclcmd = [tclcmd, 'matlabcp u_spec_display -mfunc specdisplay'];

The force command applies stimulus to the clock and reset signals.

tclcmd = [tclcmd, 'force sim:/specdisp_top/clk_enable 1 0',...
                  'force sim:/specdisp_top/reset 1 0, 0 20 ns',...
                  'force sim:/specdisp_top/clk 1 0 ns, 0 40 ns -r 80ns'];


% Add "if any" user tcl commands at the end.
if exist('UsrTclCmds','var')
    tclcmd(end+1)=UsrTclCmds;
end

Start ModelSim®

Now we start ModelSim via the vsim command. The 'tclstart' property causes the specified Tcl commands to be run at startup. To run the simulation, use the run command in ModelSim, specifying the appropriate simulation time. For example type run 100000 in ModelSim. We see the figure updating as the simulation proceeds. Be sure to quit ModelSim and shut down the MATLAB server by using hdldaemon kill once you are done with this example as each time the example is run, a new ModelSim is started. we can also specify RunMode='Batch' or 'CLI' or 'GUI' before running this example. If unspecified the default run mode is 'GUI'.

if exist('RunMode','var')
    vsim('tclstart',tclcmd,'runmode',RunMode);
else
    vsim('tclstart',tclcmd);
end
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