Chapter 1. Introduction
7
technology to prove the fault-tolerance concept.
The second LEON2 VHDL design
was used in the processor device AT697 from Atmel (F) and various system-on-chip de-
vices. These two LEON implementations were developed by ESA. Gaisler Research, now
Aeroflex Gaisler, developed the third LEON3 design and has announced the availability
of the fourth generation LEON, the LEON4 processor[
1.3.5
The OpenRISC Microprocessor
OpenRISC is the original flagship project of the OpenCores community. This project
aims to develop a series of general purpose open source RISC CPU architectures. The
first (and currently only) architectural description is for the OpenRISC 1000, describing
a family of 32 and 64-bit processors with optional floating point and vector processing
support.
A team from OpenCores provided the first implementation, the OpenRISC 1200, written
in the Verilog hardware description language. The hardware design was released under
the GNU Lesser General Public License (LGPL), while the models and firmware were
released under the GNU General Public License (GPL). A reference SoC implementa-
tion based on the OpenRISC 1200 was developed, known as ORPSoC (the OpenRISC
Reference Platform System-on-Chip).
The instruction set is a reasonably simple MIPS-like traditional RISC using a 3-operand
load-store architecture, with 16 or 32 general-purpose registers and a fixed 32-bit instruc-
tion length. The instruction set is mostly identical between the 32 and 64 bit versions
of the specification, the main difference being the register width (32 or 64 bits) and
pagetable layout. The OpenRISC specification includes all features common to mod-
ern desktop/server processors: a supervisor mode and virtual memory system, optional
read, write and execute control for memory pages, and instructions for synchronization
and interrupt handling between multiple processors[
1.4
Floating point arithmetic
In computer science the programs or the circuits that are implemented to deal wih
calculations, always deal with natural numbers. Since the fundamental basis of the