Amber ARM-compatible 32-bit RISC Core Processor

Amber ARM-compatible 32-bit RISC Core Processor


Category: Processor

Created: December 23, 2010

Updated: January 27, 2020

Language: Verilog

Other project properties

Development Status: Stable

Additional info: Design done, FPGA proven, Specification done

WishBone compliant: Yes

WishBone version: n/a

License: LGPL


The Amber processor core is an ARM-compatible 32-bit RISC processor. The Amber core
is fully compatible with the ARM® v2a instruction set architecture (ISA) and is
therefore supported by the GNU toolset. The Amber project provides a complete embedded
system incorporating the Amber core and a number of peripherals, including a UART, a
timer and an Ethernet MAC.


There are two versions of the core provided in the Amber project. The Amber 23 has
a 3-stage pipeline, a unified instruction & data cache, a 32-bit Wishbone
interface, and is capable of 0.75 DMIPS per MHz. The Amber 25 has a 5-stage
pipeline, seperate data and instruction caches, a 128-bit Wishbone interface,
and is capable of 1.05 DMIPS per Mhz. Both cores implement exactly the same ISA
and are 100% software compatible. The cores do not contain a memory management
unit (MMU) so they can only run the non-virtual memory variant of Linux. The
cores has been verified by booting a 2.4 Linux kernel.

The cores were developed in Verilog 2001, and are optimized for FPGA synthesis.
For example there is no reset logic, all registers are reset as part of FPGA
initialization. The complete system has been tested extensively on the Xilinx SP605
Spartan-6 FPGA board. The full Amber system with the A23 core uses 32% of the
Spartan-6 XC6SLX45T-3 FPGA Look Up Tables (LUTs), with the core itself
occupying less than 20% of the device using the default configuration, and running at
40MHz. It has also been synthesized to a Virtex-6 device at 80MHz.

The older v2a version of the ARM instruction set is supported because it is still
fully supported by the GNU tool chain and is not covered by patents so can be
implemented without a license from ARM. For a description of the ISA, see
Archimedes Operating System - A Dabhand Guide or
Acorn RISC Machine Family Data Manual

For project documentation, see amber-user-guide.pdf and amber-core.pdf.
After reading the project documentation you can find further help on the Amber A23 Core page on the opencores forum.