Key findings: 5X to 32X faster low-power verification using Palladium XP emulation
It’s hot in July in Korea, and not just the temperature; the ideas, too. The ideas that flowed at CDNLive Korea were exciting, and that includes a very interesting talk by Jiyeon Park from the System LSI division of Samsung Electronics. His talk, titled “Enabling Low-Power Verification using Cadence Palladium XP,” struck a chord with the audience and the highlights bear sharing in this forum. This blog captures some of the highlights from the public talk in Seoul this summer.
If you are familiar with the breadth of the product lines at Samsung Electronics, you will appreciate the diversity of the end-market requirements that they must fulfill. These markets and products include:
What all of these markets have in common is that energy efficiency is now an integral and leading part of the value equation. For design teams, a good knowledge of power helps the evaluation and use of a host of critical decisions. From design architecture, IP make-versus-buy decisions, and manufacturing process selection, to the use of low-power design techniques, all are critically influenced by power.
Using simulation for low-power verification
Once the decision to overlay power reduction design techniques, such as power shutdown, has been made, new dimensions have been added to the already complex SoC verification task. The RTL verification environment is first augmented with a power intent file; in this case, IEEE 1801 was the format. The inclusion of this power intent information enables the examination of power domain shutdown, isolation operations, proper retention, and level shifting.
Figure 1: Incisive SimVision power verification elements example
Low-power verification using emulation
Simulation for low-power verification works well, so why emulation? One word—complexity! It is easy to forget that “design complexity” (usually measured in gates or transistors) is not that same as “verification complexity” (which is really hard to measure). Consider a design with four power domains, three of which are switchable and one that is switchable but also has high- and low-voltage states. That yields nine basic states, and 24 modes of operation to test. Although some of those modes may not be consequential, when paired with hundreds or even thousands of functional tests, you can begin to understand the impact of overlaying low power on the verification problem. Thus, it becomes very desirable to enlist the raw computational power of emulation.
Power off/on scenario on Palladium XP platform
A typical functional test would be augmented to include the power control signals. For power shutoff verification, for instance, the cycles for asserting isolation begin the sequence, followed by state retention, and then finally a power shutdown of the domain must be asserted to verify operation. The figure below calls out a number of checks that ought to be performed.
Figure 2: Power shutoff sequence and associated checks to make
IEEE 1801 support in Palladium XP platform
The IEEE 1801 support found in the Palladium PX platform includes some noteworthy capabilities, as well as some implications to the user. First is a patented memory randomization provided by the Palladium XP platform. This capability includes randomization of memory during shutdown and power up, control over read value during the power-off state, non-volatile memory state retention, and freezing of data on retention. The user should be aware there is about a 10%-20% capacity overhead associated with IEEE 1801-driven low-power verification.
Figure 3: Palladium low-power verification enables schedule improvement
Palladium low-power verification flow
The great thing about the emulation work flow for IEEE 1801 power verification is that the only change is to include that IEEE 1801 power intent file during the compilation stage!
Considerations for emulation environment bring-up
A Universal Verification Methodology (UVM) approach was taken by the Samsung team. This provides a unique structure to the testbench environment that is very conducive to a metric-driven methodology. Using a testbench acceleration interface, teams can run the testbench on a software simulator and the design on the emulator. In addition, the formalism allows for the case of incomplete designs that do not hinder the verification of the parts that are completed.
The most exciting part of the paper was the results that were obtained. For a minor overhead cost in compile time and capacity, the team was able to improve runtimes of their tests by 5X to 32X. Being able run tests in a fraction of the time, or many more tests in the same time, has always been a benefit for emulation users. Now low-power verification is a proven part of the value provided to Palladium XP platform users.
Figure 4: Samsung low-power verification emulation results
The key conclusions found were:
With this flow in place, the teams has begun power-aware testing that includes firmware and software verification to go along with the hardware testing. This expansion enables more capability in optimization of the power architecture. In addition, they are seeing faster silicon bring-up in the context of an applied low-power strategy.