Electrical computers and digital processing systems: memory – Storage accessing and control – Hierarchical memories
Reexamination Certificate
1998-12-22
2001-05-01
Yoo, Do (Department: 2185)
Electrical computers and digital processing systems: memory
Storage accessing and control
Hierarchical memories
C711S149000, C711S156000, C703S013000, C714S741000, C716S030000
Reexamination Certificate
active
06226716
ABSTRACT:
TECHNICAL FIELD
This invention relates to the field of logic simulation of electronic circuits. More particularly, this invention relates to test drivers for use in validating an electronic circuit design.
BACKGROUND OF THE INVENTION
Gordon Moore, the cofounder of Intel Corporation, made an observation and prediction that semiconductor performance would double every 18 months, with the price of the new product remaining constant with the old. This observation is now referred to as Moore's Law, and has remained relatively accurate since the early 1970s. Moore's Law illustrates the rapid advancement that has and is taking place in the electronics industry. Because of this rapid advancement, the market window for many electronic products is relatively short, with faster and more powerful devices being continuously introduced. Accordingly, there is great pressure to reduce the development time for many products. To significantly reduce the development time for most electronic devices, the design time must be reduced, as the design process typically consumes a majority of the development cycle.
FIG. 1
shows a typical prior art design process for an ASIC (Application Specific Integrated Circuit) device. ASIC devices are commonly used to implement large and/or high performance circuit designs. In a first step, a hardware architect typically determines the requirements for the circuit design and formulates an underlying framework of the function and projected performance characteristics of the circuit design. The architect documents these ideas in a functional specification, as shown at step
12
.
The design is then partitioned into a number of blocks and given to one or more logic designers for implementation. The logic designers create a detailed logic design using the functional specification as a guide. Rather than creating schematics, many logic designers express their design in a behavioral language such as VHDL (VHSIC Hardware Description Language), as shown at step
14
. Many logic simulation tools can directly accept behavioral language descriptions as input. This not only improves efficiency in developing complex circuit designs, but also allows various sections of the circuit design to be functionally verified before the entire design is complete.
Next, and as shown at step
16
, the design is typically logically simulated to verify the functionality thereof. To logically simulate the design, the circuit designer typically provides one or more test input files. The test input files may include a number of test conditions expressed as test vectors or the like. Each of the test vectors may include a value for selected inputs of the circuit design along with an expected circuit response. The logic simulator reads the test input files, simulates the behavior of the circuit design using the test input, and provides a simulated circuit response. The simulated circuit response is then compared to the expected circuit response to determine if the circuit design provides the expected behavior.
After logic simulation is complete, the design is typically passed to one or more physical designers, as shown at step
18
. The physical designers place the various cells that represent the basic logic building blocks of the circuit design, and interconnect the cells using a routing tool. Timing information may be extracted and analyzed by both the physical and logical designers. Some timing problems can be fixed by the physical designer by adjusting the drive strengths of various components or placing cells in a different arrangement relative to each other. As shown at step
22
, other timing problems can only be resolved by modifying the logic itself. If a problem is resolved by modifying the logic, the modified design must typically be re-verified by re-executing logic simulation step
16
and then the physical design step
18
.
After all the logical and physical changes are made, and the design meets the stated requirements, the design is released for fabrication, as shown at step
24
. Fabrication can take several months for a typical ASIC device. Once completed, the device is returned and tested, as shown at step
26
. If the device does not meet the stated requirements, a design modification may be required as shown at step
22
, forcing another design iteration of the logic simulation step
16
, the physical design step
18
, and the fabrication step
24
. Once the device meets all of the stated requirements, the device is released, as shown at step
30
.
In most design processes, it is important to reduce the number of design iterations that are required to produce a fully functional device. One way of reducing the number of design iterations is to increase the fault coverage of the test cases used during the logic simulation process. Increasing the fault coverage, however, tends to increase the time needed to generate and simulate the increased number of test cases. Thus, there is often a trade-off between an increased fault coverage and design cycle time.
FIG. 2
illustrates a prior art logic simulation process. At step
42
, the architect and test designer discuss the logic implementation and define a series of test cases that address the various functional sections and possible interactions of the design. In many designs, such as a directory based MSU (Main Storage Unit) with multiple parallel ports and crossbar switches (see below), there are many possible functional operations and interactions that could and should be tested to achieve a high fault coverage. Some test cases can be defined relatively easily. Other test cases, such as those that test the parallel and often conflicting operations of the hardware, can be much more difficult to define and implement.
Once the test cases are defined, the test designer often codes the test cases into a format that can be used to produce an input for the logic simulator. This format may include, for example, a force command, followed by a run command, followed by a force command, etc. Test cases written in this format must typically be interpreted by the logic simulator, and more particularly, by a simulation control program of the logic simulator. The simulation kernel must usually be interrupted before the simulation control program can process a subsequent line in the coded test case. Because the simulation kernel must typically be regularly interrupted, the speed of the logic simulation can be significantly reduced.
To increase the speed of the logic simulation, a test driver may be used. A test driver is typically expressed using a behavioral language description and simulated along with the circuit design. Because the test driver can be actually simulated along with the circuit design, the test driver can stimulate the inputs of the circuit design without having to be interpreted by the simulation control program, and thus without having to interrupt the simulation kernel.
Prior to simulation, the test driver can be loaded with test data for controlling the inputs of the circuit design and verifying the results of a subsequent logic simulation. The test data can be stored in a memory structure expressed within the behavioral description of the test driver. For example, the test data may be loaded into a RAM structure within the test driver, and during logic simulation, the address to the RAM structure may be incremented to provide each of the test vectors to the inputs of the circuit design.
To generate the test data, a designer often codes the desired test cases into a standard programming language like “C”, as shown at step
44
. When executed, the “C” programs generate the test data, which as indicated above, is later loaded into a memory structure within the test driver, as shown at step
46
. The “C” programs may also generate corresponding initialization files that can be loaded into the device under test (e.g. MSU RAMs). To perform the tests, clocks are issued (simulation starts), as shown at
48
.
During or at the end of the logic simulation, the results are checked to see if the test passed or failed, as shown
Bauman Mitchell A.
Ganske David L.
Crompton Seager and Tufte, LLC
Johnson Charles A.
Kim Hong
Starr Mark T.
Unisys Corporation
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