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What is an ASIP?


April 16, 2021

ASIP stands for “application-specific instruction-set processor” and simply means a processor which has been designed to be optimal for a particular application or domain.

General-purpose vs. domain-specific or application-specific processors

Most processor cores to date have been general-purpose, which means that they have been designed to handle a wide range of applications with good average performance. This may mean that if you have some special computationally intensive algorithm, such as audio processing, you may need a high-performance core (for example with a SIMD unit, or zero overhead loops) or a high clock frequency to achieve your needs. This may result in exceeding your silicon or power budget.

An alternative is to create an ASIP which has a specialized architecture, optimized to efficiently achieve the required performance for the audio processing. The ASIP would not usually be designed to optimally handle more generic operations such as those needed for an operating system. Instead, if an OS is needed, you would probably run it on a separate general-purpose core which would not be constrained by the need to run audio processing algorithms. Thus, the ASIP design is optimized for performance with just enough flexibility to meet its use case.

ASIPs have been the subject of research in universities around the world and have been applied to a number of domains such as audio signal processing, image sensors, and baseband signal processing. Codasip founder and President Karel Masařík with CTO Zdeněk Přikryl researched design automation for ASIPs at the TU Brno. To read more on their research, check the papers listed at the end of this article.

ASIPs to address semiconductor scaling issues

ASIPs or domain-specific processors are likely to be used more widely in the future due to semiconductor scaling issues. For decades, developers of SoCs have relied on Moore’s law and Dennard Scaling to get more and more performance and circuit density through successively finer silicon geometries.

While this scaling applied, it was generally reasonable to use general-purpose processor cores and to rely on new generations of silicon technology to deliver the performance required with an acceptable power consumption. However, this scaling has been known to have broken down, with smaller increments in performance improvement and leakage current worsening power consumption. Because of this, the semiconductor industry must change, and a new approach to processing is needed.

To date, this industry challenge has been tackled by incorporating different types of general-purpose cores on a single SoC. For example, mobile phone SoCs have combined application processors, GPUs, DSPs, and MCUs, but none of these classes of processor have application-specific instruction sets.

With new products demanding new algorithms for artificial intelligence, advanced graphics and advanced security, more specialized hardware accelerators are needed and are being developed. Such accelerators are designed to handle computationally demanding algorithms efficiently. Each accelerator will need an optimized instruction set and microarchitecture – in other words, an ASIP.

Domain-specific accelerators. Source Codasip.

ASIP and software development

Domain-specific processors (Application-specific processors, ASIP… you will notice we use these terms interchangeably) combine hardware specialization with flexibility through software programmability.

One challenge of creating custom hardware is ensuring the needs of software developers are met too. Techniques such as intrinsic instructions allow direct access to the instruction set from C, but reduce the flexibility of the code. They may still be a viable answer when complex functions are encapsulated in a single instruction.

But better still would be a top-down approach. Instead, a compiler created for your domain-specific accelerator, automatically targets the custom instructions you create. This, along with an instruction set simulator and profiler, accelerates the rate at which you can try different design iterations to converge on an optimal solution.

Codasip Studio provides a complete solution for this process with the ability to generate ISA and compiler from a simple instruction level model.

Design automation and verification of application-specific processors

With the need to develop many and varied accelerators, it is not efficient to develop the instruction sets and microarchitecture manually. Application software can be analyzed by profiling and the instruction set tuned to those needs. A processor design automation toolset like Codasip Studio can be then used to generate a software toolchain and an instruction set simulator.

Specifically, Codasip Studio automates the generation of a C/C++ compiler that is fully aware of the instruction set and can infer specific instructions automatically. It is important to have the C/C++ compiler in the loop, to see the impact of the application-specific instructions. The same applies for instruction set simulators, debuggers, profilers, and other tools in SDK that are automatically generated. Codasip Studio can be also used to generate hardware design including RTL, testbenches, and a UVM environment.

Did you know?

Codasip was originally founded to create co-design tools for ASIPs, hence the name “Co-dASIP”. Codasip Studio has subsequently been used for creating more general-purpose cores such as RISC-V embedded and application cores too.

Processor design does not end with generating the RTL code – the dominant part of the design cycle is verification and it needs to be rigorous. As Philippe Luc explained to Semiconductor Engineering, RTL verification is multi-layered and complex.

Codasip Studio can automate key parts of the verification process in order to help the full flow of ASIP design being quicker. Among other things, Codasip Studio provides automated coverage points for the optimised instructions. The provided UVM environment makes it easy to run programs (including the new instructions) on both model and RTL with result comparison. A constrained random program generator is provided to help closing coverage and ensure quicker verification for our customers.

To learn more about the power of Codasip Studio combined with RISC-V, read our white paper on “Creating Domain-Specific Processors with custom RISC-V ISA instructions”.

Codasip research papers on design automation for ASIP

  • MASAŘÍK Karel, UML in design of ASIP, IFAC Proceedings Volumes 39(17):209-214, September 2006.
  • ZACHARIÁŠOVÁ Marcela, PŘIKRYL Zdeněk, HRUŠKA Tomáš and KOTÁSEK Zdeněk. Automated Functional Verification of Application Specific Instruction-set Processors. IFIP Advances in Information and Communication Technology, vol. 4, no. 403, pp. 128-138. ISSN 1868-4238.
  • PŘIKRYL Zdeněk. Fast Simulation of Pipeline in ASIP simulators. In: 15th International Workshop on Microprocessor Test and Verification. Austin: IEEE Computer Society, 2014, pp. 1-6. ISBN 978-0-7695-4000-9.
  • HUSÁR Adam, PŘIKRYL Zdeněk, DOLÍHAL Luděk, MASAŘÍK Karel and HRUŠKA Tomáš. ASIP Design with Automatic C/C++ Compiler Generation. Haifa, 2013.
Roddy Urquhart

Roddy Urquhart

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What does RISC-V stand for?


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RISC-V stands for ‘reduced instruction set computer (RISC) five’. The number five refers to the number of generations of RISC architecture that were developed at the University of California, Berkeley since 1981. It is pronounced “risk-five” and you might sometimes see it written “RISC five“ or “R5“).

The RISC concept (like the parallel MIPS development in Stanford University) was motivated by the fact that most processor instructions were not used by most computer programs. Thus, unnecessary decoding logic was being used in processor designs, consuming unnecessary power and silicon area. The alternative was to simplify the instruction set and to invest more in register resources.

The RISC I project implemented a mere 31, 32-bit instructions but 78 registers. It introduced the notion of register windowing which was a technique that was later adopted by the SPARC architecture. This was closely followed by the RISC II project which had an even larger register file (138 registers). RISC II also introduced 16-bit instructions which improved code density. The terms RISC III and RISC IV have been used to refer to the SOAR and SPUR projects in 1984 and 1988, respectively.

The RISC-V project was partly motivated by the fact that proprietary, closed ISAs were restricted by patents and license agreements. Krste Asanović of the University of California, Berkeley was convinced that there were great advantages in having a free, open ISA that could be applied to both academic and industrial projects. David Patterson, who had worked on earlier RISC projects, was also involved. In 2010, a 3-month project led to the development of a new instruction set, leading to the publication of the first RISC-V ISA specification in 2011.

In order to manage contributions from other parties, the RISC-V Foundation – now RISC-V International – was formed in 2015 as an open collaborative community, and the original developers of the ISA transferred their rights around RISC-V to this organization. Since then, RISC-V International has managed further development of the RISC-V ISA.

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