Timur Tabi <ti...@freescale.com> wrote on 10/09/2009 18:13:03:
>
> Joakim Tjernlund wrote:
>
> > This calculation does not seem to match AN2919.
>
> When I wrote the code, AN2919 was much smaller than what you have today.
>
> > Suppose one used only Table 7(almost what we have if you exclude dfsr!= 1)
> > Table 7 is valid for 1 <= dfsr <=5 so how about replacing the current dfsr
> > with:
> > #ifdef __PPC__
> > u8 dfsr;
> > dfsr = (5*(i2c_clk/1000))/(100000);
> > if (dfsr > 5)
> > dfsr = 5;
> > if (!dfsr)
> > dfsr = 1;
> > debug("i2c_clk:%d, dfsr:%d\n", i2c_clk, dfsr);
> > writeb(dfsr, &dev->dfsrr); /* set default filter */
> > #endif
>
> The value of FDR is dependent on the value of DFSR, so if I calculate DFSR, I
> have to also calculate FDR. This means the table goes away. I'm okay with
> that (since my table is no longer a viable approach, it seems), but it's more
> work than I'm willing to do at the moment. Especically since this is going to
> need a lot of testing before I'm willing to push it.
I could not resist so I did a quick start:
#include <stdlib.h>
#include <stdio.h>
#define I2C_CLK 133332000
int main(int argc, char *argv[])
{
unsigned long A,B,C;
unsigned long divisor, req_div;
unsigned long curr_div = ~0;
unsigned long speed;
if (argc != 2) {
printf("%s <speed in HZ>\n", argv[0]);
exit(1);
}
speed = atol(argv[1]);
req_div = I2C_CLK/speed;
C = (5*(I2C_CLK/1000))/(100000);
if (!C)
C = 1;
for(A=10;A <= 30; A+=2) {
for (B=16; B<=2048;B*=2) {
divisor = B * (A + (3*C/B)*2);
if (divisor > req_div && divisor < curr_div) {
printf("div:%d, A:%d, B:%d\n", divisor, A, B);
curr_div = divisor;
}
}
if (A == 20)
A+=2;
if (A == 24)
A+=4;
}
printf("\nreq_div:%d, curr_div:%d, DFSR:%d\n", req_div, curr_div, C);
}
This should be useful I hope. The special treatment for A == 20 and A == 24
is a bit strange though, do they really jump like that?
Jocke
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