On Tue, Sep 17, 2013 at 9:09 PM, Andrew McLaren <and...@aratika.co.nz> wrote:
> The logic maintains a reference timebase using the timer B module (this
> simply ticks away in the background and maintains a reference counter). To
> obtain a time reference at any time, the logic stops the timer block, reads
> the TBR, and restarts the timer block. Nothing really fancy there.
Why are you stopping the timer? I understand that the timer updates
asynchronously, so the value may not be stable, but you can get around
that by taking multiple readings until you see two that are the same:
unsigned read_timer(void)
{
unsigned base, sample;
sample = TB0R;
do {
base = sample;
sample = TB0R;
} while (base != sample);
return sample;
}
Given the device erratum, this approach would probably make more
sense. It works as long as the clock is somewhat slower than your CPU
clock (like 16x slower).
-William
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