What are the best practices for testing and debugging FPGA and ASIC designs?

Some time simulation required lot of time to simulate whole design, so plan testbench not for whole design just for block by block level, so generally make BFM(bus function model) to simulate faster. Try to simulate in two simulator before releasing design to boost confidence in design and also if any corner issue got trap.

Quick tips 1. Simulation: Use tools to catch errors early. 2. Modular Design: Break down for easier testing. 3. Through Testbenches: Cover various scenarios. 4. Debugging Tools: Inspect signals efficiently. 5. Incremental Testing: Test modules gradually. 6. Hardware Validation: Verify with real inputs. 7. Firmware Debugging: Use on-chip debuggers. 8. Documentation: Maintain detailed records. 9. Version Control: Track design changes.

Modular architecture allows engineers to develop testbenches using reusable building blocks thereby reducing redundancy and saving time. The Universal Verification Methodology (UVM) built using System Verilog class based architecture helps to create modular and reusable TB's and has its own set of guidelines and consistent coding practices for building efficient TB's, running simulations and analyzing results. UVM has a layered architecture, models transactions at a lower level, uses constrained-random stimuli, and also collects functional coverage data. This methodology has been widely used by ASIC designers and verification experts to check the correctness and ensure a bug free design.

Assertions are usually written by designers/verification engineers and these allow tremendous flexibility to verify functional behavior. In addition to these assertions, there are automatic assertions generated by formal verifier tools like Cadence IFV, Jasper which automatically generates assertions by analyzing the RTL. Some of the checks include dead code checks, FSM checks, arithmetic/range overflow checks, simulation synthesis mismatch checks etc. These assertions can be utilized to eliminate common functional design errors and make sure the code is clean before verification starts. They help to improve design quality, and shorten the effort required for verification.

Formal verification can be applied right away once the RTL is ready without waiting for the traditional verification environment bring up. It helps to find bugs weeks earlier and reduces RTL changes needed at the end and also helps to save time during later stages of verification.

Debugging on hardware is only possible for FPGAs. ASICs need to be extensively verified in simulation. Because of the extreme cost of ASIC development, there are many emulation platforms which allow large ASIC designs mapped to custom hardware and simulated at higher speeds than possible with software based simulation. FPGA emulation is one of these methods where an ASIC design or a subset thereof can be mapped to it for higher speed testing.

- Try to simulate or interface the actual hardware and software functionality of the interconnected system. The closer we can get to the real system , the better test results can be achieved. This will avoid any surprises in real world .

The testing environment should be fully automated. All design changes should be kept in a version control system ala git and any new checkings have to be subject to all existing tests periodically (daily weekly). As more test are produced, these tests should also be added to the regression suite. All the results of periodic tests should be available in an easily accessible dashboard along with the coverage provided by all the tests. This will give everyone involved in the design of the system a good idea who the design & verification is going and whether tape-out is possible on a timely basis.

One thing is practice and other is mathod. Good practices include 1. Good Test bench design which includes all test cases, boundary conditions, toggle of all bits of control element, maximum or theoretically full coverage of design, data test patterns for thorough testing of memory location and lines 2. Prepare good test plan same as simulation verification, Good record-keeping of results so that as test progresses debugging can be easily done Good Mathods include 1. Use of automation technologies as signal tap which acquire ASIC or FPGA pin status through JTAG circuitery and provide results on GUI 2. Automation of test sequences through combination of software and hardwares

One thing which is very important in digital logic verification is how different ASIC and FPGA flows are. In an FPGA, the base hardware is fully verified, all the mixed-signal blocks like transceivers, PCIe and built-in ADC etc work perfectly as long as they configured correctly. So one has to test only the user produced logic. Not to say that this is trivial but compared to an ASIC it’s a much simpler task. Also the turnaround time for an FPGA and cost of reimplementation is much lower, in order of days and very little monetary cost. An ASIC on the other hand takes 4-5 months to respin and multi-million dollars in cost. Not to mention that all non-digital blocks need to be verified too. Full verification is much more important for ASICs.

In my experience I have found that knowing the operation of the actual system helps in creating a good design and a comprehensive test bench. Don't just focus on verification and simulate but also add test cases as per the actual system behavior. So it's important to actually understand the system operation as an FPGA/ASIC designer.

Just for testing we use DFT approach scan cell, ATPG , BIST so that any manufacturing level defect can also be trap. During ASIC Design we insert scan flops so that it will help us in testing.