do eurorack pmod calibration properly

[matpalm]

couldn't work out the right way to do calibration so ended up with a hack on both the verilog and training side :/

from notes ( see 2023 10 17 )

sending +5V => 20,000    ( that's from the COUNT_PER_VOLT = 4000 ) 

...

just realised that +/-5V => +/- 20_000
could be mapped to +/-5V => +/- 5_000 with  >>> 2;
and then back with << 2 ?

this works. and 5000 is close to 4096...

so can we need to rescale on the way in?

i.e. we want 5V = 16_384    ( since 16384 >> 2 = 4096 )
so we want to 0.8192

currently 16384 is 4.096V
so we want to divide everything in the data by 

in fact, even simpler....

if we map everything by >>> 2 coming in  ( and by << 2 on way out )
then we have 5V = 5000 = 0x1388 = 1.220703125

the data is based on 8V=1.0, so 5V = 0.625
so we just need to multiply all the data by 1.220703125/(5/8)=1.953125 
during training....

means the max the net will take, or output, is +/- 1.22 but this should be fine and is well with FP4.12