Re: C compiler pointer management on DSPs

David Brown <david.brown@hesbynett.no>
Sun, 29 Sep 2019 10:53:35 +0200

          From comp.compilers

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From: David Brown <david.brown@hesbynett.no>
Newsgroups: comp.compilers
Date: Sun, 29 Sep 2019 10:53:35 +0200
Organization: A noiseless patient Spider
References: 19-09-003 19-09-004 19-09-006 19-09-007 19-09-009 19-09-015 19-09-017
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Keywords: DSP, architecture, C
Posted-Date: 30 Sep 2019 18:06:34 EDT
Content-Language: en-GB

On 28/09/2019 20:19, Derek M. Jones wrote:
> George,
>
>> Just curious - what DSPs have 48-bit characters?
>
> Motorola DSP56000 Family Optimizing C Compiler uses 24 bits
> TMS320C3x/C4x Optimizing C Compiler uses 32 bits
>
> I remember reading a compiler manual and thinking, wow, that's
> unusual.


24-bit DSP's have been popular for audio applications. (There is also
the TPU, a specialised RISC processor used for timer applications in
engine control microcontrollers, that is 24-bit.)


Some processors have larger access sizes to simplify the hardware. The
first DEC Alpha, and some ARM designs, had no instructions for reading
or writing 8-bit or 16-bit data. In effect, these had 32-bit (maybe on
the Alpha it was 64-bit) "byte" sizes. But smaller access sizes could
be easily simulated in software.


I can't think of any application where 48-bit would such a natural fit
that you'd have it as your basic access unit. Some video DSP's have
used 48-bit units, but that is for a vector of 3 16-bit colour units.



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