Announcement

Many tried, all got kicked in the back by ARM. If you can create something useful, get ready for a contact from one of their lawyers,

Andras Tantos

why write it from scratch? the nnARM source codes can be found with google with no problems. the synthesis result is unfortunatly quite big fits barely into XC2S600E

would be nice to have smaller core though ;)

antti PS the ARMlayers tried to take nnARM off from public internet, but its still downloadable, so the layers are not doing very good job.

Doesn't really matter, good enough in this case, lets any potential commercial user get the message loud & clear. If its a 600 target, thats one very expensive Arm compared to real thing. For an opensource cpu to be useable, it must be competitive in size, speed, power with commercial cpus.

johnjaksonATusaDOTcom

I wrote my own clone earlier this year (just haven't got around to releasing it yet). I spent quite a bit of time studying the patent issues, and believe that you should be able to implement the basic V4 instruction set (This doens't include Thumb). The only real hurdle is then likey to be patent 5,386,563 which deals with the exception processing mechanism. However, I believe this patent to be invalid, as there is a significant amount of prior art (Search for "ARM's dubious patents" in comp.arch).

Cheers, JonB

I'm not sure if it has been worked on since the last time I saw it, but I don't believe the nnARM could really be used as is. Didn't it just come with a behavioural memory interface? I also seem to remember the pipeline being pretty shallow, meaning it isn't exactly going to go very fast.

Cheers, Jon

And if you want to be better than the competition, don't base your design on ARM. It has (IMHO) a huge flaw in the architecture (shifting), that means if you want decent performance, you end up having to add tons of extra logic.

Jon

Does anyone know when the arm license is going to expire?

I think the exception processing patent was filed around 90-92, so its got quite a bit in it left..

JonB

If you only need binary compatibility with user-mode ARM software, you can implement a different exception handling mechanism and avoid the patented technique entirely.