[sdiy] was how_you_got_started...

[rsdio at audiobanshee.com]

On Sep 26, 2015, at 12:44 AM, Thomas Strathmann <thomas at pdp7.org> wrote:
> On 26/09/15 04:31, Scott Gravenhorst wrote:
>> Yes, I found this to be true by doing it.  I've been able to write a
>> nice additive flute model monosynth for dsPIC33F in C, but my best
>> efforts at polysynths are in assembly language.  The main issue for me
>> is the fact that there is no native data type support for 16 bit fixed
>> point arithmetic.  Worse yet is that sometimes designs need more than
>> one definition for 16 bit fixed point.  Usually 1.15 works, but there
>> are times other configurations are necessary.  This is rather difficult
>> and at least ugly in C even using typedef etc.  Just ugly.  And in C I
>> had to write several functions in assembly language anyway that handle
>> the use of DSP instructions because they are not used by the C compiler
>> even if it's logical to do so.  At least in my experience...  can anyone
>> tell me how to make an FIR filter in C30 that uses the MAC
>> instruction... ??
> 
> What about using C++ for such cases. Seems like a good fit for hiding the complexity of custom arithmetic code. Probably not ideal, but surely better than writing raw assembly code all the way.

The origin of the problem is that C does not have fixed-point types. Sure, you might be able to cover that up as much as possible in the source by using C++, but it's not as straightforward as using assembly, because assembly does have support for fixed-point.

I'm surprised there isn't a C derivative that has native support for fixed-point, and which would therefore possibly optimize well on a DSP platform.

Even though I generally prefer to use C for most development because it is faster, especially for high level, broad scope coding, there are times when assembly is actually faster and easier. Assembly usually wins when the scope is focused in a narrow area, or when C simply doesn't have the necessary types to represent what's actually going on in the hardware. Mixing C and assembly usually gives the best overall advantage. If you put the high performance math in assembly subroutines, then you can orchestrate at a high level from C without ever touching individual fixed-point samples.

Brian