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Codasip’s Expanding RISC-V Offering


July 22, 2020

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In the last three months, Codasip’s RISC-V processor offering has expanded considerably. For some years, Codasip has supplied Bk3 and Bk5 RISC-V cores aimed at low- to medium-complexity embedded applications. But recently four additional cores have joined the Codasip RISC-V offering.

Three of the cores, the SweRV Core™ EH1, EH2 and EL2, were designed by Western Digital and were open-sourced through CHIPS Alliance. These 32-bit cores are mainly aimed at high-performance embedded applications and complement the existing 32-bit Bk3 and Bk-5 cores. The EH1 offers outstanding embedded performance due to its superscalar, dual issue architecture. Even more performance is delivered by the EH2 which provides two hardware threads (harts). The EL2 core is more compact and is a single-issue core.

The RTL for all three SweRV Cores is available on GitHub free of license fees. However, RTL alone is not sufficient to use a SweRV Core in an SoC design. Firstly, a complete software toolchain is needed to allow embedded software to be developed. Secondly, a comprehensive EDA design flow needs to exist to undertake simulation, static analysis, and synthesis of the core’s RTL. It is important that the core can be easily integrated with peripherals, memories, and buses in order to implement a sub-system. EDA design flows need to keep up with revisions in both the processor IP and the EDA tools.

In December 2019, Western Digital and Codasip announced that they were cooperating to enable the deployment of open-source SweRV Cores in production silicon. Codasip’s SweRV Core Support Package (SSP) provides all of the components necessary to design, implement, test, and write software for a SweRV Core-based system-on-chip, including but not limited to verification testbenches and intellectual property, reference scripts for leading EDA flows, models for simulation and emulation, and software development tools.

The Support Package is available in a Free version consisting of open-source components and mainly aimed at academic use, and in a Pro version aimed at commercial SoC design using commercial EDA tools. The SweRV Core Support Package for EH1 was released in April and support for EH2 and EL2 was added in June. In addition, Codasip offers services for customizing SweRV Cores.

Although the semiconductor industry regularly talks of comparing processor cores in terms of performance versus complexity or in terms of PPA (performance, power, area), both performance and complexity have different aspects. Many Systems-on-Chip (SoCs) use multiple cores and face different requirements for different functions. For example, a core for a subsystem such as Wi-Fi will have quite different needs to one running a feature-rich OS such as Linux.

The Codasip Bk7 RISC-V core, announced yesterday, is Codasip’s first application processor. Like all previous Bk core designs, it has been designed in the Codasip Studio processor design system. This means that its architecture can be readily modified to create application-specific processors.  It has all the features needed for running embedded Linux and will be the cornerstone for further application processor developments. The Bk7 core is a 64-bit core with a 7-stage pipeline and memory management unit (MMU). Future versions of the Bk7 will support symmetric and heterogenous multi-processing.

In future posts we will be looking into some of the different facets of processor performance and complexity in order to see how the expanded Codasip offering can be applied to varying applications. We will also provide more detailed information on the Bk7 processor core.

 

Roddy Urquhart

Roddy Urquhart

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What is SweRV Core EH2?


June 4, 2020

In mid-May, CHIPS Alliance announced the open sourcing of the SweRV Core™ EH2 and SweRV Core EL2 designed by Western Digital. These cores, as well as the earlier EH1, are now supported by Codasip’s SweRV Core Support Package which provides all of the components necessary to design, implement, test, and write software for a SweRV Core-based system-on-chip. But what is SweRV Core EH2?

The SweRV Core EH1 was the first to be released through CHIPS Alliance and was a core aimed at high-end embedded applications including Western Digital’s flash controllers and SSDs. The core is a dual issue, superscalar, high-performance core with 9 pipeline stages. The EH2 is an exciting further development aimed at delivering even more performance for IoT, artificial intelligence and data-intensive embedded applications.

The EH2 breaks new ground for RISC-V cores by being the world’s first dual threaded, commercial RISC-V core. Its 9-stage pipeline is based on that of the EH1, but it contains additional resources to support dual threading. There are doubled RISC-V general purpose registers, control and status registers, fetch buffers, instruction buffers, and other logic. By adding these incremental resources, the EH2 allows the host software to effectively ‘see two cores’. The simulated performance of the dual threaded EH2 core is an outstanding 6.3 CoreMark/MHz.

The SweRV Core EH2 supports machine mode only, meaning that it is aimed at applications using real-time operating systems or bare metal software. It has four 64-bit AXI4 bus interfaces for instruction fetch, load/stores, debug, and for accessing optional closely coupled memories. There is an optional instruction cache with either parity-based or ECC-based error protection, an optional instruction closely coupled memory (ICCM), and an optional data closely coupled memory (DCCM) which use ECC-based error protection.

The open-source RTL for the SweRV Core EH2 is available from CHIPS Alliance. However, considerably more than just RTL is needed to integrate the core into a system-on-chip (SoC) and to develop the associated firmware. A considerable amount of effort will be needed to create the EDA flows in particular and to maintain them over multiple RTL and EDA software versions.

The SweRV Core Support Package (SCSP) contains everything needed to deploy a Western Digital SweRV™ EH2 core in an integrated circuit, providing support for both EDA tool flows and embedded software development. SCSP saves the considerable effort that would be needed to set up EDA flows for the EH2 core from scratch. The SweRV Core Support Package for EH2 is available in both basic Free and Pro versions.

The Free version consists of open-source deliverables and infrastructure for using open-source EDA tools and an SDK. Users can access an internet forum for support.

The Pro version combines open-source and commercial deliverables. It provides flows, examples and models for using commercial EDA tools. This version includes professional support by e-mail and telephone.

Roddy Urquhart

Roddy Urquhart

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