How to optimize bit bang interface?

Hi there,

I am trying to configure an Altera FPGA using the so called "passive serial interface". Basicly it follows the scheme "clk low, data out, clock high".

For testing I wrote the loop

                 ts = get_timer (0);
                 while (1) {
                         if (get_timer (ts) > 10 * CFG_HZ)
                                 break;
                         /* Deassert the clock */
                         (*fn->clk) (FALSE, TRUE, cookie);
                         /* Assert the clock */
                         (*fn->clk) (TRUE, TRUE, cookie);
                 };

fn->clk() is the function that the common FPGA code uses:

int inline fpga_clk_fn(int assert_clk, int flush, int cookie)

{
         if (assert_clk)
                 *AT91C_PIOB_SODR = FPGA_DCLK;
         else
                 *AT91C_PIOB_CODR = FPGA_DCLK;
         return assert_clk;
}

I noticed that this is awfully slow. I get arounf 50kHz using an AT91RM9200 running at 51MHz (core @ 171MHz).

Could someone give me a hint how to optimize stuff like this for speed?

Thanks a million,

Steven Scholz

imc Measurement & Control               imc Me?systeme GmbH
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