[sdiy] Raspberry Pi 2 Synthesizer Project

[Scott Gravenhorst]

Regarding NEON...

I'm using gcc version 5.3.0 (and I'm compiling on the Rpi2 itself).

The configuration is set --with-float=hard.

I did some experiments and noticed that when gcc is used with -S (and no 
-o) it will generate a .s file with assembly instructions.  One can see 
NEON instructions in the output file (such as vadd.f32).  Apparently, 
this installation of gcc (on my Rpi2) is configured to default to using 
hardware floating point since without any special or additional switches 
it will generate NEON instructions.  I also tried to use the NEON 
intrinsics which worked, but was somewhat slower than letting the 
compiler vectorize and implement the algorithm.  I tested using a simple 
single pole low pass IIR filter.  I managed to turn off NEON and the 
output code was about 5 times slower.

--ScottG