GateManPoly DAC Window analysis:

  reg [11:0] DACreg = 12'b100000000000;    // Data for SPI DAC
  reg [5:0] WINDOW;   // register holds the number of shifts of the window

WINDOW is updated by sysex.

// DAC
  reg  [20:0] NEXT_DAC;  
  wire [11:0] DAC_WIN;             // 12 bit movable window
  wire [20:0] DAC_SHIFTER;         // wider than DAC
  assign DAC_SHIFTER = NEXT_DAC << WINDOW;
  assign DAC_WIN = DAC_SHIFTER[20:9];   


In the DACena state of the state machine:

      DACreg <= {~DAC_WIN[11],DAC_WIN[10:0]};

The structure {~DAC_WIN[11],DAC_WIN[10:0]} replaces the need to 
add 12'h800 to convert signed values to the unsigned DAC requirement.

This scheme is for the 12 bit DAC on the S-3Esk.  It has notably poorly
named registers.

_____________________________________________________________________________

For SVF_Drum starting with ver_j, the DAC window idea has been expanded to 
accomodate a 24 bit signed DAC.  

The name of some objects have been changed:

WINDOW is renamed to WINDOW_SHIFTS


