Hugo Villeneuve wrote:
> Round the serial port clock divisor value returned by
> calc_divisor().
>
> Signed-off-by: Hugo Villeneuve <[EMAIL PROTECTED]>
>
> ---
>
> Rounding is important, especially when using high baud rates
> values like 115200bps. When using the non-rounded value, some
> boards will work and some won't.
>
> drivers/serial/serial.c | 7 ++++++-
> 1 files changed, 6 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/serial/serial.c b/drivers/serial/serial.c
> index 76425d8..7e315ad 100644
> --- a/drivers/serial/serial.c
> +++ b/drivers/serial/serial.c
> @@ -124,6 +124,8 @@ static NS16550_t serial_ports[4] = {
>
> static int calc_divisor (NS16550_t port)
> {
> + u32 divisor_x10;
> +
> #ifdef CONFIG_OMAP1510
> /* If can't cleanly clock 115200 set div to 1 */
> if ((CFG_NS16550_CLK == 12000000) && (gd->baudrate == 115200)) {
> @@ -144,8 +146,11 @@ static int calc_divisor (NS16550_t port)
> #else
> #define MODE_X_DIV 16
> #endif
> - return (CFG_NS16550_CLK / MODE_X_DIV / gd->baudrate);
>
> + /* Compute divisor value with rounding by adding 0.5 */
> + divisor_x10 = (10 * CFG_NS16550_CLK) / MODE_X_DIV / gd->baudrate;
> +
> + return (divisor_x10 + 5) / 10;
> }
>
> #if !defined(CONFIG_SERIAL_MULTI)
Hi Hugo,
Will a real rounding work? Work better? If I got my mental math and
parenthesis right and the resulting math doesn't overflow your
registers, the following will add 1/2 the baud rate scaled by the
MODE_X_DIV and then perform the divide which will do full rounding.
return (((CFG_NS16550_CLK + ((gd->baudrate / 2)* MODE_X_DIV))
/ MODE_X_DIV) / gd->baudrate);
Alternately, I prefer to scale up by 16 and then divide by 8 since
processors can do that very efficiently ( << 4 followed by >> 3).
Best regards,
gvb
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