[sdiy] DSP coding (was: how you got started with your current µC? (was: Re: Most common ICs))

[Richie Burnett]

> A lot depends on the DSP you are using. If you are using a higher end DSP
> that has pipe lines and multiple ALUs then using the C compiler will get 
> you
> the best performance unless you're some sort of uber programmer. There are
> way too many things going on in those processors to keep track of and the
> compilers have been optimized to handle that stuff. But for the smaller 
> DSPs
> like the MicroChip ones assembly language is the way to go if you really
> want the performance.
>
> Jay S.

Just reading Jay and Brian's comments here and I totally agree.  A fellow 
DSP programmer once told me that the key to good DSP performance is ensuring 
that the "processing pipelines are being continuously pumped".  Basically if 
a MAC unit is sat there doing nothing for a significant amount of time, then 
that is wasted resource.  On something like a dsPIC platform there is only a 
single MAC unit, and it's not pipelined, so it's fairly easy to code in 
assembly so that the MAC unit always has data and is kept busy most of the 
time, so you get good performance.  However, as Jay said, higher end DSPs 
have multiple MAC units, or multiple whole DSP cores, deep pipelining, 
additional dedicated filtering and sample-rate converter modules, etc.  It 
is much harder to keep track of all of this stuff in your head as a 
programmer, and to make sure all of the modules are kept pumped with data, 
so it's best to use a dedicated compiler that's been written to sort this 
stuff out.

FWIW, I got into DSP programming about 20 years ago through my day job 
writing embedded software for instrumentation and measurement applications. 
(Most recent work project is summarised in the research paper "Electronic 
Detection Strategies for a MEMS-Based Biosensor".)  Started messing about 
with audio DSP using an Analog Devices EZ-kit lite (ADSP2181) board around 
the same time that Propellerhead software brought out Rebirth!

-Richie,