[avr-gcc-list] Speed challenge...

[Rob Ward]

Hi. I have a challenge. The (working) code below outputs 19 bits 
serially from a 4433 uC to another chip using data, clock, and strobe 
lines. The data comes from 3 lookup arrays of 256 bytes each. At 4MHz on 
a 4433 uC , it takes about 87us to send all 19 bits. I wonder if there 
is a faster way of doing the job?

Rob

///////////////////////////////////////////////////////////////////
// send 19 configuration bits
///////////////////////////////////////////////////////////////////
void Send_Word(u08 Step_Pos) {
 u08 mask, data, i;

 mask = 0x80;
 data = PRG_RDB(&Word_Hi[Step_Pos]);

 __cbi(PORTD,6);                       // set strobe low to initiate 
data transfer

 for (i=0; i<=7; i++) {                // send first 8 bits

   __cbi(PORTD,5);                     // set clock line low

   if (mask & data)                    // present data
     __sbi(PORTD,4);
   else
     __cbi(PORTD,4);

   __sbi(PORTD,5);                     // clock the data bit

   mask >>= 1;
 }

 mask = 0x80;
 data = PRG_RDB(&Word_Mid[Step_Pos]);

 for (i=0; i<=7; i++) {                // send first 8 bits

   __cbi(PORTD,5);                     // set clock line low

   if (mask & data)                    // present data
     __sbi(PORTD,4);
   else
     __cbi(PORTD,4);

   __sbi(PORTD,5);                     // clock the data bit

   mask >>= 1;
 }

 mask = 0x80;
 data = PRG_RDB(&Word_Lo[Step_Pos]);

 for (i=0; i<=2; i++) {                // send first 8 bits

   __cbi(PORTD,5);                     // set clock line low

   if (mask & data)                    // present data
     __sbi(PORTD,4);
   else
     __cbi(PORTD,4);

   __sbi(PORTD,5);                     // clock the data bit

   mask >>= 1;
 }

 __sbi(PORTD,6);                       // reset strobe to high to 
terminate data transfer
} // End Send_Word()                    // (don't care what state the 
data line holds upone exiting here)




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