When I need to read a timer asynchronously do three consecutive reads and
do a bitwize majority function on them.
On Wed, Sep 18, 2013 at 11:08 PM, William Swanson <swanson...@gmail.com>wrote:
> 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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