Gaisler would be easier one to implement in ASIC. The Leon4 is a 4-core variant. In any case, the Leon3 and key I.P. are GPL'd specifically for open-source to build on it. SPARC ISA only require $99 fee to use SPARC-compatible line. OSS people just keep ignoring it. Meanwhile, academics have built on it and the Leon3FT variant is often used in space applications.
So, get either booting on a FPGA, install Linux, and have at it. :)
RISC-V is the best open one to get on right now. The ISA is well-designed plus open. There are simulators, high-speed CPU's, compilers, and so on for it. Surprisingly, many big companies are also backing it on top of the academics doing it. There's at least a dozen RISC-V implementations in progress.
Note: OpenRISC is not RISC-V. It was a competing ISA that's fallen to the wayside as RISC-V's popularity soared. It did get used in Milkymist IIRC. Best to ignore it except maybe out of personal curiosity in favor of RISC-V and SPARC.
http://www.gaisler.com/index.php/products/processors/leon3
http://www.oracle.com/technetwork/systems/opensparc/index.ht...
Gaisler would be easier one to implement in ASIC. The Leon4 is a 4-core variant. In any case, the Leon3 and key I.P. are GPL'd specifically for open-source to build on it. SPARC ISA only require $99 fee to use SPARC-compatible line. OSS people just keep ignoring it. Meanwhile, academics have built on it and the Leon3FT variant is often used in space applications.
So, get either booting on a FPGA, install Linux, and have at it. :)