[Tremor] Tremor lowmem on TI 55x DSP

John Ripley jripley at rioaudio.com
Wed Oct 6 02:57:16 PDT 2004

>-----Original Message-----
>From: EXTERN Wacker Klaus (Extern; CM-DI/ESP1)
>Sent: 06 October 2004 08:40
>To: tremor at xiph.org
>Subject: [Tremor] Tremor lowmem on TI 55x DSP
> I try to port Tremor lowmem on TI 55x DSP. 
> I am not familiar with the 54x and actually I just started to work with
the 55x. 
> But here is a short summery 
> 55x                    54x 
> 2 16bit MAC            1 17bit MAC 
> 3 data read busses     2 data read busses 
> 2 data write busses 
> 32 KW (64KB) DRAM      ? 
> 64 KW (128KB) SRAM     ? 
> Better DMA 
> Can only address words(2 bytes, can you believe this)   ? 
> Fast SDRAM interface                                    ? 
> Instruction cache                                       ? 
> The ALUs seemed to be similar
> Because of only three read data busses (stupid ) the two MACs have to
share one
> parameter (or it is a constant which is in register)
> Therefore the two MACs do not produce the double amount of MAC operations 
> Thanks for the help 
> Klaus

Actually I think the double MAC with shared coefficient is a good design
idea and it'll give much the same performance as two whole MAC units. Easy
example: in stereo streams you'll be doing the same operation on two
independent arrays using the same coefficients. Less obvious example: the
real and imaginary parts of a complex multiply in a radix-2 FFT can still be
done simultaneously.

Usually I find I'm just wasting instructions doubling up coefficients in
SIMD multipliers (e.g Intel MMX/SSE). I'm guessing the TI 55x implementation
takes way less silicon and battery.

- John Ripley.

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