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HDL Cosimulation

Cosimulate HDL design by connecting Simulink with HDL simulator

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  • Library:

  • HDL Verifier / For Use with Cadence Xcelium

    HDL Verifier / For Use with Mentor Graphics ModelSim

    HDL Verifier / For Use with Xilinx Vivado Simulator

  • HDL Cosimulation block
  • HDL Cosimulation block
  • HDL Cosimulation block

Description

The HDL Cosimulation block cosimulates a hardware component by applying input signals to and reading output signals from an HDL model under simulation in the HDL simulator. Configure and generate this block using the Cosimulation Wizard. When cosimulating with the Vivado® simulator, you must first generate this block using the Cosimulation Wizard. When cosimulating with ModelSim® or Xcelium™, you can optionally bypass the wizard and configure the block directly.

You can configure these options on the block:

  • Mapping of the input and output ports of the block to correspond with signals (including internal signals) of an HDL module. You must specify a sample time for each output port. You can optionally specify a data type for each output port. Vivado cosimulation does not support mapping of internal signals.

  • Type of communication and communication settings used to exchange data between simulators.

  • The timing relationship between units of simulation time in Simulink® and the HDL simulator.

  • Rising-edge or falling-edge clocks to apply to your model. You can specify the period for each clock signal.

  • Tcl commands to run before and after the simulation.

You can use this block to model a source or sink device by configuring the block with input or output ports only.

Compatibility with Simulink Code Generation

  • This block participates in HDL code generation with HDL Coder™. The coder generates an interface to your manually written or legacy HDL code. It does not participate in C code generation with Simulink Coder™.

Ports

The ports shown on the block correspond with signals from your HDL design running in the HDL simulator. The Ports tab displays the HDL signals that correspond to the ports.

When using Xcelium or ModelSim simulators, You can add and remove ports, and configure their data types and sample times, by changing the block parameters. Use the Auto Fill button to fill the table via a port information request to the HDL simulator. This request returns port names and information from your HDL design running in the HDL simulator (this step is not necessary if you used the Cosimulation Wizard to generate the block). See Get Signal Information from HDL Simulator.

All signals that you specify when you configure the HDL Cosimulation block must have read/write access in the HDL simulator. Refer to the HDL simulator product documentation for details.

Input

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The ports on the block correspond with ports on your HDL design. Add or remove ports on the Ports tab.

Data Types: int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean | Fixed-point

Output

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The ports on the block correspond with ports on your HDL design. Add or remove ports on the Ports tab.

Data Types: int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean | Fixed-point

Parameters

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This property is read-only.

This section displays information after you generate this block using the Cosimulation Wizard. It displays the following items:

  • HDL Simulator – Vivado simulator

  • HDL Design Library – Location of HDL library files

  • HDL Language – VHDL or Verilog

  • HDL Time Precision – Time precision of HDL design

  • HDL Waveform File – Name and path of waveform file

When generating a cosimulation block for Vivado simulator, you cannot change the names and directions of ports, clocks, resets, or time precision using the block mask. To change these items, open the Cosimulation Wizard and regenerate the block.

Dependencies

This parameter is visible only when you use Vivado cosimulation.

Ports

Eliminates the one output-sample delay difference between the cosimulation and Simulink that occurs when your model contains purely combinational paths. Clear this check box if the HDL Cosimulation block is in a feedback loop and generates algebraic loop warnings or errors. When you simulate a sequential circuit that has a register on the data path, specifying direct feedthrough does not affect the timing of that data path.

Specify the signal path name using the HDL simulator path name syntax. For example, manchester.samp for Xcelium HDL simulators. The signal can be at any level of the HDL design hierarchy. The HDL Cosimulation block port corresponding to the signal is labeled with this name.

For rules on specifying port and module path names in Simulink, see “Specify HDL Signal/Port and Module Paths for Cosimulation”.

You can copy signal path names directly from the HDL simulator wave window and paste them into the Full HDL Name field. Use the Path.Name view and not Db::Path.Name view. After pasting a signal path name into Full HDL Name, click Apply to complete the paste operation and update the signal list.

Dependencies

If the block was generated from the Cosimulation Wizard, this value should not be changed. For the Vivado HDL Cosimulation block the parameter is read-only.

To add a bidirectional port, add the port to the list twice, as both input and output.

Input — HDL signals that Simulink drives. Simulink deposits values on the specified HDL simulator signal at the specified sample rate.

Note

When you define a block input port, make sure that only one source is set up to drive input to that signal. For example, avoid defining an input port that has multiple instances. If multiple sources drive input to a single signal, your simulation model produces unexpected results.

Output — HDL signals that Simulink reads. For output signals, you must specify an explicit sample time. You can also specify the data type, but the width must match the width of the signal in HDL. For details on specifying a data type, see the Data Type and Fraction Length parameters.

Simulink signals do not have a tristate semantic because there is no 'Z' value. To interface with bidirectional signals, connect to the input and enable signals of both the output driver and the output signal of the input driver. This approach leaves the actual tristate buffer in HDL, where resolution functions can handle interfacing with other tristate buffers.

Dependencies

If the block was generated from the Cosimulation Wizard, this value should not be changed. For the Vivado HDL Cosimulation block the parameter is read-only.

This property is read-only.

Displays the type of the HDL port signal, as configured by the Cosimulation Wizard.

Dependencies

This parameter is visible only if the block was generated for use with Vivado cosimulation.

This property is read-only.

Displays the dimensions of the HDL port signal, as configured by the Cosimulation Wizard.

Dependencies

This parameter is visible only if the block was generated for use with Vivado cosimulation.

Time interval between consecutive samples applied to an output port.

Simulink reads a value from the associated HDL simulator signal at the sample rate specified here.

In general, Simulink handles port sample periods as follows:

  • If you connect an input port to a signal that has an explicit sample period, based on forward propagation, Simulink applies that rate to the port.

  • If you connect an input port to a signal that does not have an explicit sample period, Simulink assigns a sample period that is equal to the least common multiple (LCM) of all identified input port sample periods in the model.

  • You must specify an explicit sample time for each output port.

The HDL time corresponding to the Simulink sample time hits depends on the Timescales setting. See Simulation Timescales.

Dependencies

To enable this parameter, set I/O Mode to Output.

Select Inherit to automatically determine the data type. The block checks that the inherited word length matches the word length queried from the HDL simulator. If they do not match, Simulink generates an error message. For example, if you connect a Signal Specification block to an output, Inherit forces the data type specified by the Signal Specification block onto the output port.

If Simulink cannot determine the data type of the signal connected to the output port, it queries the HDL simulator for the data type of the port. As an example, if the HDL simulator returns the VHDL® data type STD_LOGIC_VECTOR for a signal of size N bits, the data type ufixN is forced on the output port. The implicit fraction length is 0.

You can also assign an explicit data type, with optional Fraction Length. By explicitly assigning a data type, you can force fixed-point data types on output ports of the HDL Cosimulation block. For example, for an 8-bit output port, setting the Sign to Signed and setting the Fraction Length to 5 forces the data type to sfix8_En5. You cannot force width. The width is always inherited from the HDL simulator.

The Data Type and Fraction Length properties apply only to the following types of HDL signals:

  • VHDL signals of any logic type, such as STD_LOGIC or STD_LOGIC_VECTOR

  • Verilog® signals of wire or reg type

Dependencies

To enable this parameter, set I/O Mode to Output.

During cosimulation with the Vivado simulator, this parameter is displayed as Simulink Data Type.

Sign designation for explicit output port data type.

Dependencies

To enable this parameter, set I/O Mode to Output, and set Data Type to Fixedpoint.

Size, in bits, of the fractional part of a fixed-point output signal. For example, for an 8-bit output port, setting the Sign to Signed and setting the Fraction Length to 5 forces the data type to sfix8_En5. You cannot force width; the width is always inherited from the HDL simulator.

Dependencies

To enable this parameter, set I/O Mode to Output, and Data Type property to Fixedpoint.

The Data Type and Fraction Length properties apply only to the following types of HDL signals:

  • VHDL signals of any logic type, such as STD_LOGIC or STD_LOGIC_VECTOR

  • Verilog signals of wire or reg type

Clocks

Note

During cosimulation with the Vivado simulator, this tab is named Clocks, Resets, Enables.

Create optional rising-edge and falling-edge clocks that apply stimuli to your cosimulation model. The scrolling list displays HDL clocks that drive values to the HDL signals that you are modeling, using the deposit method. The clock signals must be single-bit signals. Vector signals are not supported. For instructions on adding and editing clock signals, see Creating Optional Clocks with the Clocks Pane of the HDL Cosimulation Block.

Specify the time required for the HDL simulation to run before starting the cosimulation. Specify a nonnegative integer, and select time units from the menu.

  • fs – Femtoseconds

  • ps – Picoseconds

  • ns – Nanoseconds

  • us – Microseconds

  • ms – Milliseconds

  • s – Seconds

Dependencies

To enable this parameter, generate this block for Vivado cosimulation.

Specify each clock as a signal path name, using the HDL simulator path name syntax. For example: /manchester/clk or manchester.clk.

For information about and requirements for path specifications in Simulink, see Specify HDL Signal/Port and Module Paths for Simulink Test Bench Cosimulation.

You can copy signal path names directly from the HDL simulator wave window and paste them into the Full HDL Name field. Use the Path.Name view and not Db::Path.Name view. After pasting a signal path name into Full HDL Name, click Apply to complete the paste operation and update the signal list.

Dependencies

If the block was generated from the Cosimulation Wizard, this value should not be changed. For the Vivado HDL Cosimulation block the parameter is read-only.

Select one of the following options.

  • Rising – Specify a rising-edge clock.

  • Falling – Specify a falling-edge clock.

The periods and durations are Simulink times. To relate Simulink times to HDL times, go to the Timescales tab and click Determine Timescale Now.

Dependencies

This parameter is visible only for ModelSim or Xcelium cosimulation.

For Vivado cosimulation, select one of the following options.

  • Active Rising Edge Clock – Create a periodic signal with 50% duty cycle where the rising edge is offset from when Simulink drives the inputs.

  • Active Falling Edge Clock – Create a periodic signal with 50% duty cycle where the falling edge is offset from when Simulink drives the inputs.

  • Step 0 to 1 – Create a step function that starts by driving a 0 for the specified duration, then transitions to 1.

  • Step 1 to 0 – Create a step function that starts by driving a 1 for the specified duration, then transitions to 0.

The periods and durations are Simulink times. To relate Simulink times to HDL times, go to the Timescales tab and click Show Times and Suggest Timescale.

Dependencies

This parameter is visible only for Vivado cosimulation.

To specify an explicit clock period, enter a sample time equal to or greater than two resolution units (ticks).

If the clock period is not an even integer, Simulink cannot create a 50% duty cycle. Instead, the HDL Verifier™ software creates the falling edge at clockperiod/2 (rounded down to the nearest integer).

For ModelSim or Xcelium periods and durations are specified as Simulink time, and for Vivado they are specified as HDL time.

Timescales

Choose a timing relationship between Simulink and the HDL simulator, either manually or automatically. These parameters specify a correspondence between one second of Simulink time and some quantity of HDL simulator time. This quantity of HDL simulator time can be expressed in one of the following ways:

  • Relative timing relationship (Simulink seconds correspond to an HDL simulator precision, or "tick".

  • Absolute timing relationship (Simulink seconds correspond to an absolute unit of HDL simulator time)

For more information on calculating relative and absolute timing modes, see Defining the Simulink and HDL Simulator Timing Relationship.

For detailed information on the relationship between Simulink and the HDL simulator during cosimulation, and on the operation of relative and absolute timing modes, see Simulation Timescales.

To see the relationship between the Simulink times and HDL times of all of the ports, clocks, resets, and enables click Show Times and Suggest Timescale. This action also automatically determines a usable timescale if needed.

If you select this option, HDL Verifier calculates the timescale when you start the Simulink simulation. If this option is not selected, click Determine Timescale Now to calculate the timescale immediately without starting a simulation. For Vivado cosimulation, this button shows as Show Times and Suggest Timescale. Alternatively, you can manually select a timescale. For guidance through the automatic timescale calculation, see Specify Timing Relationship Automatically.

This parameter consists of a Time value and a TimeUnit value.

To configure relative timing mode for a cosimulation:

  1. Verify that Tick, the default setting for TimeUnit, is selected. If it is not, then select it from the list on the right.

  2. Enter a scale factor in the Time text box on the left. The default scale factor is 1.

To configure absolute timing mode for a cosimulation:

  1. Set TimeUnit to a unit of absolute time: fs (femtoseconds), ps (picoseconds), ns (nanoseconds), us (microseconds), ms (milliseconds), or s (seconds).

  2. Enter a scale factor in the Time text box on the left. The default scale factor is 1.

Connection

This tab is not visible during cosimulation with the Vivado simulator.

Type of connection between Simulink and the HDL simulator.

  • Full Simulation: Confirm interface and run HDL simulation.

  • Confirm Interface Only: Connect to the HDL simulator and check for signal names, dimensions, and data types, but do not run HDL simulation. During Simulink simulation, there is no contact with the HDL simulator.

  • No Connection: Do not communicate with the HDL simulator. The HDL simulator does not need to be started.

When both applications run on the same computer, you can choose shared memory or TCP sockets for the communication channel between the applications. If you do not select this option, only TCP/IP socket mode is available, and the Connection method list becomes unavailable.

  • Socket: Simulink and the HDL simulator communicate via a designated TCP/IP socket. TCP/IP socket mode is more versatile. You can use it for single-system and network configurations. This option offers the greatest scalability. For more on TCP/IP socket communication, see TCP/IP Socket Ports.

  • Shared memory: Simulink and the HDL simulator communicate via shared memory. Shared memory communication provides optimal performance and is the default mode of communication.

Dependencies

This parameter shows when you select HDL Simulator is running on this computer.

This parameter applies if you run Simulink and the HDL simulator on different computers.

Indicate a valid TCP socket port number or service for your computer system, if you are not using shared memory. For information on choosing TCP socket ports, see TCP/IP Socket Ports.

When you select this option, the HDL Cosimulation block icon displays the current communication parameter settings. If you select shared memory, the icon displays SharedMem. If you select TCP socket communication, the icon displays Socket and displays the host name and port number in the format hostname:port.

This information can help you distinguish between multiple HDL Cosimulation blocks, where each block is communicating to a different instance of the HDL simulator.

Simulation

This tab is not visible during cosimulation with the Vivado simulator.

Specifies the amount of time to run the HDL simulator before beginning simulation in Simulink. Specifying this time properly aligns the signal of the Simulink block and the HDL signal so that they can be compared and verified directly without additional delays.

This setting consists of a PreRunTime value and a PreRunTimeUnit value.

  • PreRunTime: Any valid time value. The default is 0.

  • PreRunTimeUnit: Specifies the units of time for PreRunTime.

    • Tick

    • s

    • ms

    • us

    • ns

    • ps

    • fs

The cosimulation tool executes these commands in the HDL simulator, before simulating the HDL component of your Simulink model. If you enter multiple commands on one line, append each command with a semicolon (;), the standard Tcl concatenation operator.

For example, use this parameter to generate a one-line echo command to confirm that a simulation is running, or a complex script that performs an extensive simulation initialization and startup sequence. You cannot use these commands to change simulation state.

You can specify any valid Tcl command. The Tcl command you specify cannot include commands that load an HDL simulator project or modify simulator state. For example, the character vector cannot include commands such as start, stop, or restart (for ModelSim) or run, stop, or reset (for Xcelium).

The cosimulation tool executes these commands in the HDL simulator, after simulating the HDL component of your Simulink model.

You can specify any valid Tcl command. The Tcl command you specify cannot include commands that load an HDL simulator project or modify simulator state. For example, the string cannot include commands such as start, stop, or restart (for ModelSim) or run, stop, or reset (for Xcelium).

Note

After each ModelSim simulation, the simulator takes time to update the coverage result. To prevent the potential conflict between this process and the next cosimulation session, add a short pause between each successive simulation.

Model Examples

Verify Viterbi Decoder Using HDL Cosimulation

Verify Viterbi Decoder Using HDL Cosimulation

Generate and verify HDL code to implement a fixed-point Viterbi decoder.

Open Script

Extended Capabilities

Version History

Introduced in R2008a

See Also

Topics