Gabe Moretti, Contributing Editor
Although the IP industry is about 25 years old, it still presents problems typical of immature industries. Yet, the use of IP in systems design is now so popular one is hard press to find even one system design that does not use IP. My first reaction to the use of IP is “back to the future”.
For many years of my professional career I dealt with board level design as well as chip design. Between 1970 and 1990 IP was sold as discrete components by companies such as Texas Instruments, National, and Fairchild among many others. Their databooks described precisely how to integrate the part in a design. Although a defined standard for the contents did not exist, a de-facto standard was followed by all providers. Engineers, using the databooks information would choose the correct part for their needs and the integration was reasonably straight forward. All signals could be analyzed in the lab since pins and traces were available on the board.
As semiconductors fabrication progressed, the board became the chip, and the components are now IP modules. One would think that integration would also remain reasonably straight forward. But this is not the case. Concerns about safeguarding intellectual property rights took over and IP developers were reluctant to provide much information about the functioning of the module, afraid that its functionality would be duplicated and thus they would loose sales.
As the number of transistors on a chip increases, the complexity of porting a design from one process to the next also increases.
Figure 1. Projected number of transistors on a chip
Developers found that by providing a hard macro, that is a module already placed and routed and ready for fabrication by the chosen foundry, was the best way to protect their intellectual rights. But such strategy is costly because foundries cannot just validate every macro for free. The IP provider must be in the position to guarantee volume use by the foundry’s customers. Thus many IP modules must be synthesized. This means they must be verified.
Karthik Srinivasan Corporate Application Engineer Manager Analog Mixed Signal at Apache Design Solutions, an Ansys company, wrote that “SoC designs today integrate significant number of IPs to accelerate their design times and to reduce the risks to their design closure. But the gap in the expectations of where and how the sign-off happens between the IP and SoC designers create design issues that affect the final product’s performance and release. IP designers often validate their IPs in isolation with expectations of near ideal operating conditions. SoCs are verified and signed off with mostly abstracted or in many cases ‘black-box’ views of IPs. But as more and more high speed and noise sensitive IPs get placed next to each other or next to the core digital logic failure conditions that were not considered emerge. This worsens when these IPs share one or more power and ground supply domains. For example, when a bank of high speed DDR IPs are placed next to a bank of memories, the switching of the DDR can generate sufficient noise on the shared ground network that can adversely affect the operation of the memory.
As designs migrate to smaller technology nodes, especially those using FinFET based technologies this gap in the design closure process is going to worsen the power noise and reliability closure process.”
DDR memory blocks are becoming a greater and greater portion of a chip as the portion of functionality implemented in firmware increases. Bob Smith, Senior VP of Marketing and Business Development at Uniquify makes the case for a system view of memories.
” DDR IP is used in a wide variety of ASIC and SoC devices found in many different applications and market segments. If the device has an embedded processor, then it is highly likely that the processor requires access to external DDR memory. This access requires a DDR subsystem (DDR controller, PHY and IO) to manage the data traffic flowing to and from the embedded processor and external DDR memory.
Whether it is procured from an external source or developed by an internal IP group, almost all chip design projects rely on DDR IP to implement the on-chip DDR subsystem. The integration techniques used to implement the DDR IP in the chip design can have far reaching effects on DDR performance, chip area, power consumption and even reliability.
Figure 2. A non-optimized DDR implementation
The above fiogure illustrates a typical on-chip DDR implementation. Note that while the DDR I/Os span the perimeter of the chip, the DDR PHYs are configured as blocks and are placed in such a way that they are centered with the I/Os. As shown in the diagram, this not only wastes valuable chip area, but also creates other problems. ”
” A much more efficient way to implement the DDR subsystem IP is to deliver a DDR PHY that is exactly matched to the DDR I/O layout. By matching the PHY exactly to the I/Os, a tremendous amount of area is saved and power is reduced. Even better, the performance of the DDR can be improved since the PHY-I/O layout minimizes skew.”
Figure 3. Optimized DDR block
As process technology progresses and moves from 32 nm to 22nm and then 14 nm and so on, the role of the foundry in the place and route of an entire chip increases. In direct proportion the freedom of designers to determine the final topology of a chip decreases. Thus we are rapidly reaching the point where only hardened hard modules will be viable. The number of viable providers in the IP industry is shrinking rapidly and many significant companies have been acquired in the last three or four years by EDA companies that becoming major providers of IP products.
Synopsys started selling IP around 1990 and has now a wide variety of IP in its portfolio, mostly developed internally. Cadence, on the other hand, has built its extensive inventory of IP products mostly through acquisition.
Michael Munsey, Director of ENOVIA Semiconductor Strategy at Dassault Systemes points out that there are a number of issues to deal with regarding IP.
1. IP Sourcing: Companies are going to need a way to source IP. They will need access to a cataloging system that allows for searching of both internally developed or under development IP as well as externally available third party IP.
2. IP Governance: For internally developed IP, there needs to be systems and methodologies for handling the promotion of work in progress to company certified IP. For both internal and externally acquired IP, there needs to be a process to validate that IP, and then a system to rate the IP internally based on previous use, documentation available, and other design artifacts.
3. IP Issue Defect and Tracking: Since IP will be in use in multiple projects, a formal system is required to handle issue and defect tracking across multiple projects against all IP. If one group finds and issue with a piece of IP, all other project groups that are using that IP need to be alerted of any issues found and the plan on resolving the issue. Ideally this should be integrated into design tools that are used to assemble IP as well. If a product has already gone out the door with the defective IP, these issues need to managed and corrective actions need to ensue based on any defects found.
4. IP Security: There are different levels of protection needed for different types of IP and robust methods must be put in place to ensure the security of IP. First, company critical IP must be secure, and systems need to be put in place to make sure that the IP does not leave the company premises. If collaborating with partners, any acquired IP must also be handled so that it is only used in the designs that are being collaboratively designed. There need to be restrictions on using partner IP in design blocks which in turn can become IP in other designs. There needs to be a way to track the ‘pedigree’ of IP.
5. Variant driven platform based design: Ultimately, for companies to keep up with the shortening market windows and application driven platform design, companies will need to adopt a system where there are base platforms with pre-qualified IP that can be configured on the fly and used a s a starting point for new designs. These systems would automatically populate a design workspace with the required IP from a company approved catalog as the basis of a new design moving forward.
Integrating the Pieces
Farzad Zarrinfar, Managing Director of the Novelics Business Unit at Mentor Graphics,
provided a synthesis of the problems facing designers.
“For IP Integration, multiple IP like ‘Hard IP’, ‘Synthesizable Soft Peripheral IP’, and ‘Synthesizable Soft processor IP’ with different set of deliverables, use EDA tools for efficient ASIC/SOC designs. Selecting the optimal IP size (such as smallest embedded memory IP) is a critical design decision. While free IP is readily available, it does not always provide the best solution when compared to fee-based IP that provides much better characteristics for the specific applications.
IP integration to achieve smaller die size, lower leakage, lower dynamic power, or faster speed can provide designers with a more optimized solution that can potentially save millions of dollars over the life of the product, and better differentiate their chips in a highly competitive ASIC/SoC marketplace.”
Bill Neifert, Chief Technology Officer at Carbon Design Systems observes. “Certainly, some designers at the bleeding edge differentiate every aspect of the subsystem and their own IP, but we’re increasingly seeing others adopt whole subsystem designs and then making configuration tweaks. Think black box design and ARM’s big.LITTLE offerings are prime examples of this trend.
Of course, in order to make these configuration changes, designers need to know the exact impact of the changes that they’re making. We see users doing this a lot on our IP Exchange web portal. They will download a CPAK (Carbon Performance Analysis Kit), a pre-built system or subsystem complete with software at the bare metal or O/S level. This gets them up and running quickly but not with their exact configuration. They’ll then iterate various configuration options in order to meet their exact design goals. It’s not unusual for a design team to compile 20 different configurations for the same IP block on our portal and then compare the impact of each of these different models on system performance.
Naturally, all of this impacts the firmware team quite a bit. The software developers don’t need to know exactly what the underlying hardware is doing but the firmware team needs the exact IP configuration. The sooner these decisions can be made, the sooner they can start being productive. Integrating this level of software on to the hardware typically exposes a new round of IP optimizations that can be made as well. Therefore, it’s not unusual for IP configuration changes to happen in waves as additional pieces of IP and software are added to the system.”
Drew Wingard, CTO at Sonics points out that standards matter. “Because there are many sources for IP, the industry had to create and adhere to standards for integration. From a silicon vendors’ perspective, IP sources include third-party commercial components, internally designed blocks and cores, and customer-designed components. To meet the challenge of integrating IP components from many different places, SoC designers needed communication protocol standards. Communication protocol standards efforts began with the Virtual Socket Interface Alliance (VSIA), continued with the Open Core Protocol International Partnership (OCP-IP), and today reside with Accellera. Of course, our customers need to leverage de-facto standards such as ARM’s AMBA as well. We owe our ability to integrate IP to the fundamental communication protocol standards work that these organizations performed.”
The Challenge of Verification
Sunrise’s Prithi Ramakrishnan is concerned about system verification. “At a very high level, the main issue with IP is that the simulated environment is different from the final design environment. Analog and RF IP is dependent on process/node, foundry, layout, extraction, model fidelity, and placement. So you are either tied to just dropping it in ‘as is’ and treating it like a black box (nobody knows how it works and whether it meets the required specifications) or completely changing it (with the caveat that you can no longer expect the same results). Digital IP needs to be resynthesized followed by placement and routing, and it takes several iterations to make the IP you got work the way you want it to work. In addition, this process is extremely tool-dependent.
Finally, there are system level issues like interoperability, interface and controls (how does the IP talk to the rest of the SoC). A very important, often overlooked factor is the communication between the IP providers and the SoC implementation houses – there are documents outlining integration guidelines, but without an automated process that takes in all that information, a lot could be lost in translation.”
The issue of how well a third party IP has been verified will always hunt designers unless the industry finds a way to make IP as trustworthy as the TI 7400 and equivalent parts of the early days. Bernard Murphy, CTO at Atrenta observed: “One area that doesn’t get a lot of air-time is how a SoC verification team goes about debugging a problem around an IP. You have the old challenge – is this our bug or the IP developer’s bug? If the developer is down the hall, you can probably resolve the problem quickly. If they are now working for your biggest competitor, good luck with that. If this is a commercial IP, you work with an apps guy to circle around possibilities: maybe you are using it wrong, maybe you misunderstood the manual or the protocol, may be they didn’t test that particular configuration for that particular use-case… Then they bring in their expert and go back through the cycle until you converge on an answer. Problem is, all this burns a lot of time and you’re on a schedule. Is there a way to compress this debug cycle?”
He offers the following suggestion. “One important class of things to check for is the above didn’t test that configuration for that use-case. This is where synthesized assertions come in. These are derived automatically by the IP developer in the course of verifying the IP. They don’t look like traditional assertions (long, complex sequences of dependencies). They tend to be simpler, often non-obvious, and describe relationships not just at the boundary of the IP but also internal to the IP. Most importantly, they encode not just functionality but also the bounds of the use-cases in which the IP was tested. Think of it as a ‘signature’ for the function plus the verification of that function.”
Thomas L. Anderson, VP of Marketing at Breker Verification Systems pleads: integrate, but verify. He argues that “The truth is that most SoC teams trust integration too much and verify too little. Many SoC products hit the market only after two or three iterations through the foundry. This costs a lot of money and risks losing market windows to competitors. Most SoC teams follow a five-step verification process:
- Ensure that each block, whether locally designed or licensed as IP, is well verified
- Use formal methods to verify that each block has been integrated into the SoC properly
- Assemble a minimal chip-level simulation testbench and run a few sanity verification tests
- Hand-write some simple C tests and run on the embedded processors in simulation or emulation
- Run the production software on the processors in simulation, emulation, or prototyping
The problem with this process is that the tests in steps 3 and 4 are too simple since they are hand-written. They typically verify only one block at a time, ignoring interaction between blocks. They also perform only one operation at a time, so they don’t stress cache coherency or any inherent concurrency within the design. Humans aren’t good at thinking and coding in parallel. Thorough SoC pre-silicon verification can occur only with multi-threaded, multi-processor test cases that string blocks together into realistic scenarios representing end-user applications of the chip.”
An Example of Complexity
Charlie Cheng, CEO of Kilopass gave me an example of complexity in choosing the correct IP for a design by using sparse matrix math.
With semiconductor IP comprising 90 percent of today’s semiconductor devices and memory IP accounting for over 50 percent of these complex SoCs, it’s no wonder that IP is the fastest growing sector of the overall semiconductor industry. As a result, managing third-party IP is a growing responsibility within today’s semiconductor companies. How to make the right choice from a growing quantity of IP is the major challenge facing engineering teams, purchasing departments, and executive management. The process of these groups buying IP can be viewed as a sparse matrix mathematical exercise but without the actual math formulas and data manipulation.
|1.8V||Vendor A OTP|
The table shows two dimensions of a multi-dimensional matrix representing the variables confronting the purchasing company teams. In this two-dimensional matrix, imagine three additional tables for 1.8v operations with the four foundries at 28HPL, 28HPM, and 28HP. Now, replicate this in a fourth dimension for the variable of 2.5v. Add a fifth and sixth dimension to the matrix for Vendor B’s OTP. If this were a mathematical evaluation, a figure of merit would be assigned to each cell in each plane of the multidimensional matrix.
For example, Vendor A’s OTP at 1.8v has JEDEC three-lot at 28HP at TSMC, UMC and GLOBALFOUNDRIES, similarly for 28HPM and 28HP but has only working silicon at 28LP. Vendor B’s OTP may not have received three lot qualification at any of the vendors on any of the processes, but may have first silicon or one or two lot qualification on one or more of the vendors. In the mathematical exercise, a figure of merit would be assigned to the being fully qualified, one or two lot qualified, first silicon or not taped out. Using matrix algebra, the formal mathematical exercise would return a result but an intuitive evaluation of the process would suggest vendor A with more three-lot qualifications at multiple foundries would have an edge over vendor B which did not.
The above exercise would be typical of the evaluation occurring in the engineering team. A similar exercise would be occurring in the purchasing department with terms and conditions presented in the licensing agreement and royalty schedule each vendor submits. Corporate and legal would perform a similar exercise.
If the mathematical exercise was actually performed and all the cells in the matrix had assigned values, then a definitive solution is easily achieved. However, if the cells throughout the matrix are sparsely populated, then the solution ends up with a probable outcome.