ARM appears to be tolerating a number of freely available processor core clones, as long as they are based on older versions of the ARM architecture.
And so the clones keep coming. The Storm processor core is also
available from OpenCores under a license for hardware modeled on the
Lesser General Public License (LGPL) for software. Like Amber, Storm,
implements the ARMv2 instruction set architecture although the actual
hardware features of the processor core – 32-bit addresses, cache,
coprocessor bus, multiplier accumulator correspond to the ARMv3 hardware
architecture. The only thing it omits from ARMv3 is support for the
Thumb instruction set.
But others are playing with adding Thumb-2
instruction decoding to the Amber ARM processor and 16-bit only
implementations of an ARM instruction set.
Some of these enthusiasts would de well
to look at the nnARM project which is also on the OpenCores website. The project page
states: "This project is disabled or hasn't been approved yet."
The nnARM has been like that since 2001 when a clone of the ARM7 32-bit RISC
processor core, previously available free for download, was taken down
pending discussions between the core's designer – graduate student
Shengyu Shen – and a Chinese representative of ARM Holdings plc
(Cambridge, England). Prior to that event three students at Malardalen
University (Vasteras, Sweden) reported on the development of a
lightweight ARM-style processor core named BlackARM as an academic
exercise but declined to make the core available on-line.
best known is ARM's legal tussle with commercial startup PicoTurbo Inc.
(Milpitas, Calif.). ARM filed suit against PicoTurbo in March 2000
before eventually prevailing in December 2001.
But if you know of any other ARM clones – either extant today or as works in progress – please let me know.
Related links and articles:
Student's ARM7 clone disappears from the Web
Student's weigh next step with ARM7 clone
ARM gains access to picoTurbo's RISC customers in suit settlement