[peterderivaz]

It was my first job out of University to design this instruction set which may explain some of the quirkiness...

Initially the instructions did all set the status flags but it caused a tight feedback loop in the processor. The choice was between a higher clock frequency for all instructions or better 64-bit arithmetic.

None of the initial video applications needed 64-bit support so it lost out, although I did get to put in the divide instruction just so my Doom port could run faster :)

[hermanhermitage]

Love the design of the instruction set. It was a lot of fun reverse engineering it and mulling over the design space. Thanks.

[david-given]

That's awesome! Also, Doom uses divisions?

Are you allowed to tell us what the C compiler used internally was based on? I know there are some very easy to port proprietary compilers which commonly don't see the outside world, and I'm wondering whether it was one of those, or whether some poor sucker had to port gcc.

[peterderivaz]

We paid a company called Metaware to make a compiler. I believe this compiler is still in use.

As it happens, while we were waiting for this compiler to be made for us, I ported GCC to the architecture for my own use. I don't remember it being all that painful, just a few pages of machine description and everything seemed to work fine.

This only supported the scalar instruction set. However, when we needed an MP3 decoder I found that it really needed 32bit precision to meet the audio accuracy, so I also made a different port of gcc that targeted the vector processor. I changed the float data type so any mention of float actually represented 16 lanes of a 16.16 fixed point data type implemented on the vector processor. From what I recall, mp3 decode required 2MHz of the processor for stereo 44.1kHz.

[pcwalton]

> Also, Doom uses divisions?

Well, it's 3D, so you pretty much need perspective divide at the very least…