A Simulink/SMASH co-simulation interface Version October 2003

Transcription

1 A Simulink/SMASH co-simulation interface Version October 2003 TABLE OF CONTENTS 1. Introduction Why this interface? Principle Example: Spring-mass-damper system with a positive zero-crossing counter. A multidomain application Simulation Conclusion References Introduction This paper presents the first version of the Simulink/SMASH interface. It allows to integrate VHDL and Verilog s into Simulink, and lets SMASH join the Simulink environment for co-simulating these s. First, it explains the interests in such an interface and its principle. Secondly, it will focus on a full running example based on a simple springmass-damper system. This system illustrates the interface capabilities for simulating mechatronic systems. 2. Why this interface? Increasing time to market pressures, higher design complexity, and emergence of multidomain systems enlarges the need to simulate heterogeneous systems. These systems are often modelled with different tools and different languages and co-simulation technologies become the only way to provide full system simulation. Simulink is predestined to provide a real-world simulation environment including the following physical domains: mechanic, electric, fluidic, thermodynamic, etc.. It is a MATLAB-toolbox for dynamic simulations and handles systems that are described with continuous or discrete differential equations. Thus these systems can represent all physical domains. Differential equations can be modelled in Simulink in a graphical way using simple s, as shown later in the example. Through its graphical way of system arrangement and the hierarchical use of subsystems, Simulink suits perfectly into a top-down design flow and is valuable for rapid prototyping. SMASH is the only genuine mixed signal, multi-level simulator on the market today, so it perfectly fits your needs for mixing analog and logic circuits. Mixed signal means that SMASH handles both analog or continuous-time signals, and discrete-time signals, i.e. logic (binary) or digital (decimal). SMASH enjoys multi language capability. It is compatible with SPICE, Verilog-HDL, VHDL, ABCD (C-language) and VHDL-AMS. October

2 By linking Simulink and SMASH, it is now possible to fill the gap between systemlevel and HDL design. New simulation possibilities are offered by: enabling you to bring any HDL back into the system co-simulation in order to validate the behavior of each in the MATLAB system. This way, you increase your calibration level by ensuring HDL and system-level models are equivalent. providing multi-domain simulation (electrical, mechanical,...) Later releases of this interface will be extended to the use of analog models designed in SPICE and VHDL-AMS allowing you to benefit from the mixed simulation capabilities of SMASH This makes SMASH offer unequalled opportunities in the area of system design & verification. 3. Co-simulation principle The interface is based on a master/slave interaction between the two simulators. Simulink acts as the master-simulator, which calls SMASH at the beginning of the simulation as its slave (see Figure 1) The co-simulated HDL is instantiated into the Simulink model thanks to a wrapper based on a C MEX S-Function (see [2]) which has a compatible interface to the HDL. During the simulation, the two simulation kernels are synchronised and share data on their I/O as follow: CALL SIMULINK (MASTER) Matlab Matlab Matlab HDL wrapper SMASH (SLAVE) foreign_in HDL foreign_out foreign_in C Mex API S-Function core SMASH API Figure 1 Simulink and SMASH co-simulate a VHDL October

3 5. Example: Spring-mass-damper system with a positive zero-crossing counter. A multi-domain application. In this chapter a short description and a derivation of the spring-mass-damper system is given, and the simulation results will be shown. The spring-mass-damper system is shown in Figure 2. x 0 x D m R Figure 2: The spring-mass-damper system The system is built upon the following formulas: Spring force: Damping force: Acceleration force: F s F d F a = D x = R x& = m & x R D Differential equation: & x x& x = 0 m m With the following appropriate parameters: Spring constant: Damping constant: Mass: D = 0, 4 R = 0, 5 N m kg s m = 4, 0kg The entire Simulink spring-mass-damper system schematic is shown in Figure 3. October

4 Figure 3: Entire Simulink spring-mass-damper system To count the positive zero-crossings of this oscillator, a counter is integrated into the system, which is implemented in VHDL (see Figure 4). 1. entity counter is 2. port(toggle : in real; 3. count : out real); 4. end counter; 5. architecture drive_counter of counter is 6. begin 7. plus_one:process(toggle) 8. variable value : real := 0.0; 9. begin 10. if toggle = 1.0 then 11. value := value + 1.0; 12. else value := value; 13. end if; 14. count <= value; 15. end process plus_one; 16. end architecture drive_counter; Figure 4: VHDL description of a simple counter October

5 Next, the counter is linked to the oscillator in the same Simulink model, in order to run the simulation of the whole system. The integration of the VHDL is done by inserting a specific which will be parameterised (Figure 5: parameter window) so as to be linked to the VHDL counter (Figure 5: chip ). The heterogeneous system simulation is provided by the co-simulation between the two simulators, MATLAB for the mechanical part and SMASH for the logic part. Figure 5: Final Simulink system with positive zero-crossing counter 6. Simulation Finally the simulation results are considered. After giving a stimulation pulse in positive x-direction, the signal of the Simulink relay sends a signal to the S-Function and so the positive zero-crossings of the mass-oscillation are counted. This is shown in Figure 6. In Figure 7 one can see the SMASH simulation results. The same signal trace of the counter_out signal and the signal test.count_map shows the interactivity and data exchange between Simulink and SMASH. October

6 Figures 6+7: Simulink & SMASH cosimulation results October

7 7. Conclusion With this kind of interface between Simulink, MathWorks MATLAB toolbox for modelling, simulating and analysing dynamic systems, and SMASH the multi-level, mixedsignal simulator from Dolphin Integration, a new era of system design begins. It is now possible to integrate HDL s, and soon s of other languages, into any system environment to analyse their behaviour. This is not only valuable for rapid prototyping, but also for fine adjustment of certain system parts. This will especially take effect on MEMS design, where mixed-signal and mixed-domain simulations are a must. 8. References [1] Le Marrec, Valderrama, Hessel, Jerraya, Attia, Cayrol: Hardware, Software and Mechanical Cosimulation for Automotive Applications" International Workshop on Rapid System Prototyping 1998 [2] The MathWorks: Using Simulink, the official guide to Simulink Version 5 [3] The MathWorks: Writing S-Functions, the official guide to Simulink S-Function programming October