[PATCH] cpm2: Round the baud-rate clock divider to the nearest integer.
Laurent Pinchart
laurentp at cse-semaphore.com
Sat Nov 22 03:04:56 EST 2008
Hi Scott,
On Thursday 20 November 2008, Scott Wood wrote:
> On Thu, Nov 20, 2008 at 01:32:23PM +0100, Laurent Pinchart wrote:
> > Instead of rounding the divider down, improve the baud-rate generators
> > accuracy by rounding to the nearest integer.
> >
> > Signed-off-by: Laurent Pinchart <laurentp at cse-semaphore.com>
>
> This makes things worse on mpc8272ads -- the result of the division is
> 13.56, but I only get error-free serial output when rounding down. I
> don't think the remote end has timing problems, as I don't see this with
> any other board.
I get exactly the opposite here with an mpc8248 base board. Rounding down
makes 115200bds completely unreliable :-/
Could you measure the serial baudrate with and without the patch using an
oscilloscope ?
> Possibly the crystal is a little off,
That's always possible.
> or maybe it's just better to be a little too fast than a little too slow for
> some reason?
>
> Maybe we should change CPM_CLK to be MAIN_CLK/4 rather than MAIN_CLK/16
> when the BRG clock is below a certain frequency.
Isn't that the job of the boot loader ? Accuracy would be improved, but power
consumption will raise as well :-/
Best regards,
Laurent Pinchart
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