Introduction

The LEON5 processor and the GRLIB IP library has support for Xilinx Kintex Ultrascale devices. This support consists of a techmap layer that wraps specific technology elements such as memory macros and pads. GRLIB also contains a template designs for developments boards such as the Xilinx Kintex UltraScale FPGA KCU105 Evaluation Kit and infrastructure that automatically builds project files for Xilinx Vivado and synthesis tools such as Mentor Precision Hi-Rel and Synopsys Synplify Premier. More information about GRLIB and Cobham Gaisler IP cores is available on the SoC library page.

Example designs

Cobham Gaisler provides prebuilt bitstreams of the Xilinx Kintex UltraScale FPGA KCU105 Evaluation Kit LEON5 template design. These bitstreams are intended for evaluation of software running on a LEON5 SoC. To evaluate these designs, the following items are required:

• Xilinx Kintex UltraScale FPGA KCU105 Evaluation Kit
• Workstation with GNU/Linux or Microsoft Windows
• Xilinx software to program FPGA
• Bitstream, available further down on this page
• GRMON3 debug monitor - GRMON3 evaluation version (version 3.2.9 or later is required)

The example design collection is called LEON-XCKU-EX:

• LEON-XCKU User's Manual
• LEON-XCKU Quick Start Guide
• LEON-XCKU Xilinx KCU105 FPGA configuration file
• LEON5 documentation in the GRLIB IP Library User´s Manual

Introduction

The LEON processors and GRLIB IP library has support for the space-grade Xilinx Virtex-5QV FPGA. The Virtex-5QV support leverages the GRLIB Xilinx technology support that consists of a techmap layer that wraps specific technology elements such as memory macros and pads. GRLIB also contain template designs for a wide range of Xilinx development boards, including the Xilinx ML510 development board that is considered to be a good commercial option for prototyping V5QV designs. The GRLIB IP library infrastructure automatically builds project files for Xilinx ISE and synthesis tools such as Mentor Precision and Synopsys Synplify. More information about GRLIB and Cobham Gaisler IP cores is available on the SoC library page.

Example designs

The GRLIB IP library bitfiles package prebuilt includes bitstreams for development boards such as Xilinx ML510. The bitstreams can be used together with GRMON3 debug monitor - including the GRMON3 evaluation version.

Introduction

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:

• SPARC V8 instruction set with V8e extensions and compare-and-swap
• Advanced dual-issue pipeline
• Complex dynamic branch predictor and small branch target buffer
• Addition of Late ALU to decrease pipeline stalls
• 64-bit single-clock load/store operation
• 64-bit 4-port register file
• Hardware multiply and divide units
• Hardware floating-point support

• Non-pipelined area efficient FPU (NanoFPU) or High-performance, fully pipelined IEEE-754 FPU including hardware support for denormalized numbers (GRFPU5)

• Subsystem including processor and Level-2 cache with AXI4 backend also available

• Dhrystone*: 3.23 DMIPS/MHz  (-O3, inlining allowed)
• Coremark* : 4.52 CoreMark/MHz (-O3,-funroll-all-loops -finline-functions -finline-limit=1000)
  * All the results generated using BCC 2.0.7 toolchain

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

Software development

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.

Software compatibility

LEON5 provides backward compatibility for software designed for LEON3 and LEON4 systems with the following exceptions:

• LEON5 does not support the SPARC V8e multiply-and-accumulate (MAC) instructions
• LEON5 does not support the LEON-REX instruction set
• Software that depend on version field values to identify LEON3 and LEON4 processors will see a different version value for LEON5

When HW virtualization is implemented and enabled, these incompatibilities can be hidden by the hypervisor.

Configurations

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.

Availability

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.

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:

• High-performance pipelined GRFPU5 floating-point unit with denormalized number support
• The L2CACHE Level-2 cache controller
• GRIOMMU IO memory management unit
• Additional peripheral IP as described in the GRLIB IP Core User's Manual

Demonstration systems and documentation

GRLIB IP Library

LEON5 documentation is available in the GRLIB IP Library User's Manual - LEON5 subsystem.

FPGA programming files are also available for the following FPGA boards:

• LEON-XCKU example designs
• LEON-PF example designs

Community

Cobham Gaisler AB maintains a Discourse forum for those interested in the open source company's processor products.

Introduction

The GRLIB IP library has support for Microsemi RTG4 devices. This support consists of a techmap layer that wraps RTG4 specific technology elements such as memory macros and pads. GRLIB also contains a template design for the RTG4 Development Kit, bridges that allow to use the Microsemi FDDR memory controller and SerDes IP together with a LEON/GRLIB system, and infrastructure that automatically builds project files for Libero SoC. More information about GRLIB and Cobham Gaisler IP cores is available on the SoC library page.

Example designs

Cobham Gaisler provides prebuilt bitstreams of the Microsemi RTG4 Development Kit LEON3 and LEON4 template design. These bitstreams are intended for evaluation of software running on a LEON3 or LEON4 SoC implemented in RTG4. To evaluate these designs, the following items are required:

• Microsemi RTG4 Development Kit FPGA board
• Workstation with GNU/Linux or Microsoft Windows
• Microsemi software to program FPGA
• Bitstream, available further down on this page
• GRMON2 or GRMON3 debug monitor - The GRMON3 evaluation version supports LEON-RTG4-EX from version 3.0.6

The example design range is called LEON-RTG4-EX and includes the following IP cores:

• LEON3FT and LEON4FT multicore systems with 16 KiB instruction cache and 16 KiB data cache. The processors are also implemented with MMU and FPUs.
• LEON Debug Support Unit
• Bridge for Microsemi FDDR DDR3 SDRAM controller
• SPI Flash memory controller for boot-ROM
• Interrupt controller for 15 interrupts
• Timer module with two 32-bit timers and watchdog
• UART with FIFO
• General purpose I/O port

Further documentation can be found in the user's manual below.

• LEON-RTG4-EX User's Manual (updated 2018-05-08)
• Latest version of LEON-RTG4-EX bitstream package (updated 2018-05-08)