[Milkymist-devel] Single-Thread AEMB

[Shawn Tan]

On Monday 01 June 2009 11:41:32 pm you wrote:
> Hi,
>
> On Monday 01 June 2009 17.00.48 Shawn Tan wrote:
> > Sounds like the problems are mainly software portability issues. If an
> > application is written as a single-threaded app, it will only benefit
> > from the interrupt handling of the AEMB. Customising an app for the AEMB
> > would make it less portable.
> >
> > I'm not quite sure if a single-threaded core may be better because of the
> > wasted cycles encountered by data and control hazards.
>
> The balance is between :
>
> * having good performance with 2 threads and no hazards thanks to a good
> load- sharing between the interrupt service routine and the main program
> (other optimizations should be avoided without a heavy framework like
> OpenMP to keep portability), and
> * having good performance with only 1 thread subject to hazards, and a
> quite short pipeline plus a variety of well-known systematic techniques to
> reduce the occurrence or impact of such hazards (instruction reordering,
> loop unrolling, branch delay slots, etc.) that are already implemented in
> GCC (no extra software work required). A branch predictor could also be
> added to reduce the impact of control hazards (bimodal is quite simple and
> efficient and should fit well in FPGAs).
>
> This is only my gut feeling, but it seems in favor of the single-thread
> version.
>
> > There's only one real way to test this though - to design a
> > single-threaded version and compare them side-by-side. (=
>
> It could also be useful to have a high-level (not RTL) simulator to quickly
> test the impact of various architecture modifications (multiple way caches,
> branch predictor, multiple threads, etc.) without taking the time to go
> into the RTL design and coding.

I think that having a software simulator might be a good idea. It could also 
be helpful with development/debugging work. You guys have any ideas on writing 
one? I've never written a software CPU simulator before.

-- 
with metta,
Shawn Tan.