[sdiy] The Owl: ARM fx pedal

Eric Brombaugh ebrombaugh1 at cox.net
Wed Apr 24 20:25:18 CEST 2013


On 04/24/2013 11:15 AM, Martin Klang wrote:
> I'm not an expert, I but I understand a biquad filter requires 5 multiply and accumulate (MAC) operations per sample.
> The Cortex M4 does single-cycle MAC - see here:
> http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0439b/CHDDIGAC.html
>
> Therefore I don't think our information is inaccurate, though it could be more precise. Please correct me if you think I'm wrong!

A "traditional" DSP has multiple operand buses and address generation 
units that allow coefficient and data to be fetched in parallel with the 
MAC operations. The ARM Cortex M4 processor has individual DSP-like 
instructions but you must include other instructions to fetch operands, 
increment addresses, save results, etc. All this means that the ARM DSP 
will take significantly more instruction cycles to compute a filter than 
would a DSP.

Eric





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