[hpsdr] Blackfin 32*32 bits multiply

[Christophe DONZELOT (HB9TLN)]

There is some details in the Blackfin Hardware reference.
The 32bits mpy is microcoded
The dual MAC operation only allow doubling MAC throughput , you can 
input two 32 bits scalar into both MACs to double throughput.
One of both MAC have a shifter just after accumulator, and the MAC 
output can be a standard  32 bits register.
The  32 bits  MAC will be slower than 300 MMAC/s @ 600 MHz (4 16x16 MAC 
+ shift & 32 bits addition).

I was to quick in my reading of Analog specs .
It was an error hi !
To resume : you can only couple MACs to double throughput with 16bits 
MAC operations.

Chris
HB9TLN