[Dspforum] Programmers reference is perhaps useless :(

[Wenstrand, Doug S.]

The programmers reference for the DSPLIB doesn't really place many
restrictions on the input to DSPF_sp_biquad, so it would seem relatively
easy to use.  Unfortunately, the restrictions appear to have changed
somewhere along the way, and the reference was not updated?

In any case, the assembly source itself for the DSPLIB -- available in
your dsplib install directory as dsp67x.src
Shows the following :

ASSUMPTIONS
*
*       nx is a multiple of 3
*
*       Source and destination arrays do not overlap.   



Wow.

In any case, if you are to use biquad, this is an important restriction,
you think?


I can confirm that this is in fact correct -- if you step through the
call to biquad, the loop counter decrements by 3 each time (since the
loop is unrolled "thrice").  When you get to the end of your array, it
will go to -2, and then keep going (since -2 is not 0).  That means that
it will run through memory trashing all your other stuff.

In any case BEWARE! 



---------------------------------------
D. S. Wenstrand
Johns Hopkins University
Applied Physics Laboratory
(240) 228-4282


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