[sdiy] SHARC DSP programming
rburnett at richieburnett.co.uk
Sat Sep 24 18:21:15 CEST 2016
Anyone programming Analog Device's SHARC DSP who can answer a quick
Is there an instruction to left/right shift the MAC accumulator result (MRF
I think that surely there must be, as this is essential for normalising
results of accumulated MAC operations, but I can't find it! On the dsPIC
you can specify an accumulator shift as part of the "Round and Store
Accumulator" instruction "sac.r", where the double-word accumulator is
optionally rounded and truncated back to single-precision before being
stored. I can't seem to find a similar instruction for the SHARC, which
seems crazy, but the documentation for the instruction set is a bit of a
mess, rather than having logical groups of instructions together, etc.
The best I can come up with so far is to saturate the MAC result, then move
the multiplier result into a general purpose register, then clip it, then
left shift it to multiply by 2 or 4 or whatever. But this is many more
instructions, and it obviously doesn't shift in the bits from the lower half
of the MAC accumulator that it really should do if you do a real double-word
shift operation. There doesn't seem much point in having an extended
precision accumulator (with overflow bits added onto the left, and underflow
bits to the right,) if you can't shift it left or right to normalise it when
you store the result.
Am I missing something!?!?
More information about the Synth-diy