Set up a writable working folder outside your MATLAB® installation
folder to store files that will be generated as you complete your
tutorial work. The tutorial instructions assume that you create the
folder hdlfilter_tutorials
on drive C.
This section assumes that you are familiar with the MATLAB user interface and the Filter Designer. The following instructions guide you through the procedure of designing and creating a basic FIR filter using Filter Designer:
Start the MATLAB software.
Set your current folder to the folder you created in Create a Folder for Your Tutorial Files.
Start Filter Designer by entering the filterDesigner
command in the
MATLAB Command Window. The Filter Design & Analysis Tool
dialog box appears.
In the Filter Design & Analysis Tool dialog box, check that the following filter options are set:
Option | Value |
---|---|
Response Type | Lowpass |
Design Method | FIR Equiripple |
Filter Order | Minimum order |
Options | Density Factor: 20 |
Frequency Specifications | Units: Fs: Fpass: Fstop: |
Magnitude Specifications | Units: Apass: Astop: |
These settings are for the default filter design that the Filter Designer creates for you. If you do not have to change the filter, and Design Filter is grayed out, you are done and can skip to Quantize the Filter.
If you modified options listed in step 4, click Design Filter. The Filter Designer creates a filter for the specified design and displays the following message in the Filter Designer status bar when the task is complete.
Designing Filter... Done
For more information on designing filters with the Filter Designer, see the DSP System Toolbox™ documentation.
You must quantize filters for HDL code generation. To quantize your filter,
Open the basic FIR filter design you created in Design a FIR Filter in Filter Designer.
Click the Set Quantization Parameters button
in the left-side toolbar. The Filter
Designer displays a Filter arithmetic menu in the
bottom half of its dialog box.
Select Fixed-point
from
the Filter arithmetic list. Then select Specify
all
from the Filter
precision list. The Filter Designer displays the first
of three tabbed panels of quantization parameters across the bottom
half of its dialog box.
Use the quantization options to test the effects of various settings on the performance and accuracy of the quantized filter.
Set the quantization parameters as follows:
Tab | Parameter | Setting |
---|---|---|
Coefficients | Numerator word length | 16 |
Best-precision fraction lengths | Selected | |
Use unsigned representation | Cleared | |
Scale the numerator coefficients to fully utilize the entire dynamic range | Cleared | |
Input/Output | Input word length | 16 |
Input fraction length | 15 | |
Output word length | 16 | |
Filter Internals | Rounding mode | Floor |
Overflow mode | Saturate | |
Accum. word length | 40 |
Click Apply.
For more information on quantizing filters with the Filter Designer, see the DSP System Toolbox documentation.
After you quantize your filter, you are ready to configure coder options and generate VHDL code for the filter. This section guides you through starting the Filter Design HDL Coder™ UI, setting options, and generating the VHDL code and test bench for the basic FIR filter you designed and quantized in Design a FIR Filter in Filter Designer and Quantize the Filter.
Start the Filter Design HDL Coder UI by selecting Targets > Generate HDL in the Filter Designer dialog box. The Filter Designer displays the Generate HDL dialog box.
Find the Filter Design HDL Coder online help.
In the MATLAB window, click the Help button in the toolbar or click Help > Product Help.
In the Contents pane of the Help browser, select the Filter Design HDL Coder entry.
Minimize the Help browser.
In the Generate HDL dialog box, click the Help button. A small context-sensitive help window opens. The window displays information about the dialog box.
Close the Help window.
Place your cursor over the Folder label or text box in the Target pane of the Generate HDL dialog box, and right-click. A What's This? button appears.
Click What's This? The context-sensitive help window displays information describing the Folder option. Configure the contents and style of the generated HDL code, using the context-sensitive help to get more information as you work. A help topic is available for each option.
In the Name text box of the Target pane,
replace the default name with basicfir
. This option
names the VHDL entity and the file that contains the VHDL code for
the filter.
Select the Global settings tab of the UI. Then select the
General tab of the Additional
settings section of the UI. Type Tutorial - Basic
FIR Filter
in the Comment in header text
box. The coder adds the comment to the end of the header comment block in
each generated file.
Select the Ports tab of the Additional settings section of the UI.
Change the names of the input and output ports. In
the Input port text box, replace filter_in
with data_in
.
In the Output port text box, replace filter_out
with data_out
.
Clear the check box for the Add input register option. The Ports pane now looks like the following.
Click the Test Bench tab in the
Generate HDL dialog box. In the File name text
box, replace the default name with basicfir_tb
.
This option names the generated test bench file.
Click Generate to start the code generation process.
The coder displays messages in the MATLAB Command Window as it generates the filter and test bench VHDL files:
### Starting VHDL code generation process for filter: basicfir ### Generating: C:\hdlfilter_tutorials\hdlsrc\basicfir.vhd ### Starting generation of basicfir VHDL entity ### Starting generation of basicfir VHDL architecture ### HDL latency is 2 samples ### Successful completion of VHDL code generation process for filter: basicfir ### Starting generation of VHDL Test Bench ### Generating input stimulus ### Done generating input stimulus; length 3429 samples. ### Generating Test bench: C:\hdlfilter_tutorials\hdlsrc\basicfir_tb.vhd ### Please wait ... ### Done generating VHDL Test Bench
As the messages indicate, the coder creates the folder hdlsrc
under
your current working folder and places the files basicfir.vhd
and basicfir_tb.vhd
in
that folder.
Observe that the messages include hyperlinks to the generated code and test bench files. By clicking these hyperlinks, you can open the code files directly into the MATLAB Editor.
The generated VHDL code has the following characteristics:
VHDL entity named basicfir
.
Registers that use asynchronous resets when the reset signal is active high (1).
Ports have the following names:
VHDL Port | Name |
---|---|
Input | data_in |
Output | data_out |
Clock input | clk |
Clock enable input | clk_enable |
Reset input | reset |
An extra register for handling filter output.
Clock input, clock enable input, and reset ports are
of type STD_LOGIC
and data input and output ports
are of type STD_LOGIC_VECTOR
.
Coefficients are named coeff
,
where n
n
is the coefficient number, starting
with 1.
Type-safe representation
is used when zeros are concatenated: '0' & '0'
...
Registers are generated with the statement ELSIF
clk'event AND clk='1' THEN
rather than with the rising_edge
function.
The postfix '_process'
is appended
to process names.
The generated test bench:
Is a portable VHDL file.
Forces clock, clock enable, and reset input signals.
Forces the clock enable input signal to active high.
Drives the clock input signal high (1) for 5 nanoseconds and low (0) for 5 nanoseconds.
Forces the reset signal for two cycles plus a hold time of 2 nanoseconds.
Applies a hold time of 2 nanoseconds to data input signals.
For a FIR filter, applies impulse, step, ramp, chirp, and white noise stimulus types.
When you have finished generating code, click Close to close the Generate HDL dialog box.
Get familiar with the generated VHDL code by opening and browsing
through the file basicfir.vhd
in an ASCII or HDL
simulator editor.
Open the generated VHDL filter file basicfir.vhd
.
Search for basicfir
. This line identifies the VHDL module, using the value
you specified for the Name option in the
Target pane. See step 5 in Configure and Generate VHDL Code.
Search for Tutorial
. This section is where the coder places the text you
entered for the Comment in header option. See step 10
in Configure and Generate VHDL Code.
Search for HDL Code
. This section lists coder options you modified in Configure and Generate VHDL Code.
Search for Filter Settings
. This section describes the filter design and
quantization settings as you specified in Design a FIR Filter in Filter Designer and Quantize the Filter.
Search for ENTITY
. This line names the VHDL entity, using the value you
specified for the Name option in the
Target pane. See step 5 in Configure and Generate VHDL Code.
Search for PORT
. This PORT
declaration defines the
clock, clock enable, reset, and data input and output ports. The ports for
clock, clock enable, and reset signals are named with default character
vectors. The ports for data input and output are named as you specified on
the Input port and Output port
options on the Ports tab of the Generate HDL dialog
box. See step 12 in Configure and Generate VHDL Code.
Search for Constants
. This section
defines the coefficients. They are named using the default naming
scheme, coeff
, where n
n
is
the coefficient number, starting with 1.
Search for Signals
. This section
of code defines the signals for the filter.
Search for process
. The PROCESS
block
name Delay_Pipeline_process
includes the default PROCESS
block
postfix '_process'
.
Search for IF reset
. This code
asserts the reset signal. The default, active high (1), was specified.
Also note that the PROCESS
block applies the default
asynchronous reset style when generating VHDL code for registers.
Search for ELSIF
. This code checks
for rising edges when the filter operates on registers. The default ELSIF
clk'event
statement is used instead of the optional rising_edge
function.
Search for Output_Register
. This section of code writes the filter data to
an output register. Code for this register is generated by default. In step
13 in Configure and Generate VHDL Code,
you cleared the Add input register option, but left the
Add output register selected. Also note that the
PROCESS
block name
Output_Register_process
includes the default
PROCESS
block postfix
'_process'
.
Search for data_out
. This section
of code drives the output data of the filter.
This section explains how to verify the generated VHDL code for the basic FIR filter with the generated VHDL test bench. This tutorial uses the Mentor Graphics® ModelSim® software as the tool for compiling and simulating the VHDL code. You can also use other VHDL simulation tool packages.
To verify the filter code, complete the following steps:
Start your Mentor Graphics ModelSim simulator.
Set the current folder to the folder that contains your generated VHDL files. For example:
If desired, create a design library to store the compiled VHDL entities, packages,
architectures, and configurations. In the
Mentor Graphics
ModelSim simulator, you can create a design library with the
vlib
command.
Compile the generated filter and test bench VHDL files. In the
Mentor Graphics
ModelSim simulator, you compile VHDL code with the
vcom
command. The following commands compile the
filter and filter test bench VHDL code.
vcom basicfir.vhd vcom basicfir_tb.vhd
The following screen display shows this command sequence and informational messages displayed during compilation.
Load the test bench for simulation. The procedure for loading the test bench varies depending
on the simulator you are using. In the
Mentor Graphics
ModelSim simulator, you load the test bench for simulation with the
vsim
command. For example:
vsim work.basicfir_tb
The following figure shows the results of loading work.basicfir_tb
with the
vsim
command.
Open a display window for monitoring the simulation as the test bench runs. In the Mentor Graphics ModelSim simulator, use the following command to open a wave window and view the results of the simulation as HDL waveforms.
The following wave window displays.
To start running the simulation, issue the start simulation command for your simulator. For
example, in the
Mentor Graphics
ModelSim simulator, you can start a simulation with the
run
command.
The following display shows the run -all
command being used to start a simulation.
As your test bench simulation runs, watch for error messages. If error messages appear, interpret them as they pertain to your filter design and the HDL code generation options you selected. Determine whether the results are expected based on the customizations you specified when generating the filter VHDL code.
The following wave window shows the simulation results as HDL waveforms.