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Fastest SW SPI code

 
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thomasn101
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Fastest SW SPI code
PostPosted: Tue Feb 24, 2004 2:26 pm     Reply with quote
Hi everyone,

I want to speed up my software SPI code. With the crystal freq at 20Mhz, the transfer rate of the code below is about 270Khz. Is there anything I can do to speed it up?

Regards,
Thomas
Code:

int SW_SPI_TXRX(int dataout)
{
     int Spi_Bit_Count, Datain;

     #Asm
     Bcf       Porte, 0            // Clock Low
     Clrf      Spi_Bit_Count
     
Next_Bit:
     Bcf       Porte, 1            // Clear Data_Out Pin
     Rlf       Dataout, F
     Btfsc     Status, 0
     Bsf       Porte, 1            // Set Data_Out Pin
     
     Bsf       Porte, 0            // Clock High
     Bcf       Porte, 0            // Clock Low
     
     Bcf       Status, 0           // Clear C
     Btfsc     Portd, 3            // Check Data_In Pin
     Bsf       Status, 0           // Set C
     Rlf       Datain, F
     
     Incf      Spi_Bit_Count, F
     Movlw     8
     Subwf     Spi_Bit_Count,W
     Btfss     Status, 2           // Check Status, Z Flag
     Goto      Next_Bit
     
     Movf      Datain, W
     Movwf     _Return_
     #Endasm
}
Neutone



Joined: 08 Sep 2003
Posts: 839
Location: Houston

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PostPosted: Tue Feb 24, 2004 2:31 pm     Reply with quote
Of these two lines one is marginaly faster. This should help shave a few instructions off of your code.

for(x=8;x>0;x--)

for(x=0;x<8;x++)
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