The LEON5 is a synthesizable VHDL model of a 32-bit processor compliant with the SPARC V8 architecture. The model is highly configurable and suitable for system-on-chip (SOC) designs.
LEON5 provides backward compatibility for most software implementations that have targeted LEON3 and LEON4 processors. The LEON5 primarily targets high-end FPGA:s and deep-submicron ASIC technologies. For legacy and less performant technologies, the LEON3 processor is the recommended choice that continues to be maintained.
The processor pipeline design of the LEON5 is significantly enhanced compared to earlier LEON3 and LEON4 processors, and initial evaluations show that LEON5 can provide up to 85% faster execution for single-threaded integer benchmarks compared to LEON4. The main new feature of the LEON5 pipeline is the dual-issue functionality, allowing up to two instructions per cycle to be executed in parallel in the processor. To support the increased issue rate of the pipeline, the LEON5 has advanced branch prediction capabilities. The cache controller of the LEON5 supports a store buffer FIFO with one cycle per store sustained throughput, wide AHB slave support to enable fast stores and fast cache refill, as well as several other enhancements.
The LEON5 is interfaced using the AMBA 2.0 AHB bus (subsystem with Level-2 cache and AXI4 backend is also available) and supports the IP core plug&play method provided in the Cobham Gaisler IP library (GRLIB). The processor can be efficiently implemented on FPGA and ASIC technologies and uses standard synchronous memory cells for caches and register file. The processor supports the MUL and DIV instructions, an IEEE-754 floating-point unit (FPU) and Memory Management Unit (MMU). The cache system consists of separate I/D multi-set Level-1 (L1) caches with up to 4 ways per cache, and an optional Level-2 (L2) cache for increased performance in data intensive applications.
The LEON5 processor has the following features:
As with previous generation LEON processors, the LEON5 processor model is being continuously extended. Planned extensions for 2020 include more advanced version of LEON5 with virtualization features and higher performance bus interconnect
The LEON5 processor can be synthesized with common synthesis tools such as Xilinx Vivado, Synplify, and Synopsys DC. The processor model is highly portable between different implementation technologies.
Being SPARC V8 conformant, compilers and kernels for SPARC V8 can be used with LEON5 (kernels will need a LEON BSP). To simplify software development, Cobham Gaisler provides several toolchains and operating systems.
Debugging is generally done using the GDB debugger, and a graphical front-end such as DDD or Eclipse. The GRMON monitor interfaces to the LEON5 on-chip debug support unit (DSU), implementing a large range of debug functions. The LEON5 processor will also be supported by Cobham Gaisler's TSIM3 simulator.
LEON5 provides backward compatibility for software designed for LEON3 and LEON4 systems with the following exceptions:
When HW virtualization is implemented and enabled, these incompatibilities can be hidden by the hypervisor.
The LEON5 processor core is available as part of a subsystem that also contains system peripherals. The subsystem today only allows one primary configuration (LEON5-standard) that provides the superscalar LEON5 processor core. To support resource constrained targets, the subsystem will in a future release also support reduced variant (LEON5-small configuration). The configurations enforced by the subsystem are the ones recommended by Cobham Gaisler since they are covered by regression tests. Software toolchains provided by Cobham Gaisler are developed and built considering the same configurations. It is also possible to tailor additional configuration settings to create custom processor configurations by editing the VHDL generic (configuration parameter) assignments in the subsystem.
LEON5 is part of Cobham Gaisler's GRLIB IP Library from version 2020.2. Pre-built bitstreams for FPGA development kits are also available. The table below shows milestones for the planned future extensions to the LEON5. Please note that the milestone features and dates are tentative.
|v0||First public bitstream release. Available as LEON-XCKU example design.||2019-Dec|
Possible upgrade from LEON3/LEON4 for commercial customers. First public source release of LEON5 subsystem (GPL/COM):
Possible upgrade from LEON3/4FT for high-end rad-hard FPGA customers
First release of FT basic LEON5 subsystem for rad-hard FPGA.
Possible upgrade from LEON3/4FT for rad-hard ASIC customers
First release of FT basic LEON5 subsystem for ASIC with rad-hard stdcells: Additional FT features, support for tightly coupled memory, and internal memory scrubber.
For new customer ASIC designs. First release of advanced LEON5 subsystem for commercial, FT-FPGA and ASIC with RH stdcells: Including address-striped buses and IOMMU integration. Virtualization support.
First version of advanced LEON5 subsystem for ASIC without RH stdcells: Advanced hardening by design approach using functional redundancy.
LEON5 is part of Cobham Gaisler's free open source GRLIB IP Library. The pipelined GRFPU5 is a commercial-only offering and is not included in the free open source distribution of GRLIB. A simpler non-pipelined FPU is included in all distributions to make hardware floating point always available with the LEON5.
LEON5 is also available under a low-cost commercial license, allowing it to be used in any commercial application. The commercial LEON5 license includes:
Demonstration systems and documentation
LEON5 documentation is available in the GRLIB IP Library User's Manual - LEON5 subsystem.
FPGA programming files are also available, please see the LEON-XCKU example design.
Cobham Gaisler AB maintains a Discourse forum for those interested in the open source company's processor products.