Re: [avr-gcc-list] AVR assembly for fast bit bang

[Nils Springob]

Hi,

I think there are two problems with the code:
- using 16 bit data
- shifting by a variable number of bits
An optimization would be to write a funktion which only shifts up to 8 
bit, and to shift the data every time by one bit.

Regards,
Nils

original code:

> void write_data (Word towrite, Byte nbits)
> {
>  Byte n;
>
>  for(n = 0; n < nbits; n++)
>  {
>
>    CLK_HIGH;
>    if( towrite & (0x0001 << n))
>    {
>      SDIO_HIGH;
>    }
>    else
>    {
>      SDIO_LOW;
>    }
>    CLK_LOW;
>
>  }
> }
>  
my version:

void write_data_byte (Byte towrite, Byte nbits)
{
 while(nbits--)
 {
   CLK_HIGH;
   if (towrite&0x01)
   {
     SDIO_HIGH;
   }
   else
   {
     SDIO_LOW;
   }
   CLK_LOW;
   towrite = towrite>>1; // shift by constant value
 }
}

void write_data (Word towrite, Byte nbits)
{
 if (nbits>8)
 {
   write_data_byte((Byte)towrite, 8);
   write_data_byte((Byte)(towrite>>8), nbits-8);
 }
 else
 {
   write_data_byte((Byte)towrite, nbits);
 }
}