Shades of Sanity

Heureka!
SPI is a godsend. Everything's forgiven!

1) 8 + 1 colors at 18.868 ms, about 52 frames/sec.

The new code is approximately 2.5 x faster, which may not sound a lot - but that's what separates a boring or flickering display from a nice, crisp multicolor display. The main time thief is the "if ( *f++ >= lx)" part - the code runs at about 128 frames/sec with a fixed value instead of "b", so I figure it will be possible to further improve the code. For reference, old Williams games used 4+1 shades, newer Stern games use 16 shades.  Considering the hardware used, I'm quite satisfied with the current performance.

Feel free to look upon and possible improve the code:

void writeDisplay()
{
/*
Write all shades in one go. (i.e around 2.3 ms per color)
*/


register byte x,y,lx,b;
    register byte *f;


cli(); //Disable interrupts 

for (lx=1; lx < DISPLAY_MAX_BRIGHTNESS+1;lx++) //repeat for each color/shade
{   
   f = &frame[0][0];


//row 1  -------------
bitClear(PORTF, 2);          //set 4th bit of PORTF to LOW          
for (x=0; x < 16; x++)   //send full 128 bit row using SPI
{
if ( *f++ >= lx) b  = B10000000; else b=0;
if ( *f++ >= lx) b |= B01000000;
if ( *f++ >= lx) b |= B00100000;
if ( *f++ >= lx) b |= B00010000;
if ( *f++ >= lx) b |= B00001000;
if ( *f++ >= lx) b |= B00000100;
if ( *f++ >= lx) b |= B00000010;
if ( *f++ >= lx) b |= B00000001;

SPI.transfer(b);
}   
   bitSet(PORTF, 2);            //set 4th bit of PORTF to HIGH //Column latch
      bitSet(PORTF, 4);          //set 5th bit of PORTF to HIGH (mark first row)  
bitClear(PORTF, 5);          //set 6th bit of PORTF to LOW     
        bitClear(PORTF, 3);          //set 4th bit of PORTF to LOW
        bitSet(PORTF, 3);            //set 4th bit of PORTF to HIGH      
bitSet(PORTF, 5);            //set 6th bit of PORTF to HIGH


//row 2-31      ------------
for (y=0; y < DISPLAY_MAX_ROWS-2; y++)
{

   bitClear(PORTF, 2);          //set 4th bit of PORTF to LOW          
for (x=0; x < 16; x++)   //send full 128 bit row using SPI
{
if ( *f++ >= lx) b  = B10000000; else b=0;
if ( *f++ >= lx) b |= B01000000;
if ( *f++ >= lx) b |= B00100000;
if ( *f++ >= lx) b |= B00010000;
if ( *f++ >= lx) b |= B00001000;
if ( *f++ >= lx) b |= B00000100;
if ( *f++ >= lx) b |= B00000010;
if ( *f++ >= lx) b |= B00000001;

SPI.transfer(b);
}   
  bitSet(PORTF, 2);            //set 4th bit of PORTF to HIGH //Column latch
    bitClear(PORTF, 4);          //set 5th bit of PORTF to LOW (the rest of the rows are not leading)
  bitClear(PORTF, 5);          //set 6th bit of PORTF to LOW    
       bitClear(PORTF, 3);          //set 4th bit of PORTF to LOW
      bitSet(PORTF, 3);            //set 4th bit of PORTF to HIGH
bitSet(PORTF, 5);            //set 6th bit of PORTF to HIGH
}
 
 
//row 32 ---------------
   bitClear(PORTF, 2);          //set 4th bit of PORTF to LOW          
for (x=0; x < 15; x++)   //send full 128 bit row using SPI
{
if ( *f++ >= lx) b  = B10000000; else b=0;
if ( *f++ >= lx) b |= B01000000;
if ( *f++ >= lx) b |= B00100000;
if ( *f++ >= lx) b |= B00010000;
if ( *f++ >= lx) b |= B00001000;
if ( *f++ >= lx) b |= B00000100;
if ( *f++ >= lx) b |= B00000010;
if ( *f++ >= lx) b |= B00000001;
SPI.transfer(b);
}   
if ( *f++ >= lx) b  = B10000000; else b=0;
if ( *f++ >= lx) b |= B01000000;
if ( *f++ >= lx) b |= B00100000;
if ( *f++ >= lx) b |= B00010000;
if ( *f++ >= lx) b |= B00001000;
if ( *f++ >= lx) b |= B00000100;
if ( *f++ >= lx) b |= B00000010;
if ( *f  >= lx) b |= B00000001;
SPI.transfer(b);
  bitSet(PORTF, 2);            //set 4th bit of PORTF to HIGH //Column latch
      bitClear(PORTF, 4);          //set 5th bit of PORTF to LOW (the rest of the rows are not leading)
bitClear(PORTF, 5);          //set 6th bit of PORTF to LOW
        bitClear(PORTF, 3);          //set 4th bit of PORTF to LOW
        bitSet(PORTF, 3);            //set 4th bit of PORTF to HIGH
bitSet(PORTF, 5);            //set 6th bit of PORTF to HIGH
} //End of color/shade

sei(); //enable interrupts.


bitClear(PORTF, 5);          //set 6th bit of PORTF to LOW
}