[U-Boot-Users] [PATCH v2] Round the serial port clock divisor valuereturned by calc_divisor()

[Hugo Villeneuve]

u-boot-users-bounces at lists.sourceforge.net wrote:
> This formula is better at avoiding integer overflow.
> 
> Signed-off-by: Gerald Van Baren <vanbaren at cideas.com>
> ---
> 
> This is my latest entry in the baud rate rounding dual.  Since it
> doesn't multiply the master BRG clock but instead adds the baud rate
> scaled by 1/2 the clock multiplier, it should not overflow (for a
> master clock right at the edge of overflowing itself, it still will
> overflow, but that is pretty unlikely).
> 
> This compiles OK on the mpc7448hpc2.  I have only tested it on a
> calculator.  I have NOT tested it on real hardware.

I have tested it on my board and it works.

I also tested it on my board by using the clock value of the mpc7448hpc2 board, and printing the computed value which was correct.

>  drivers/serial/serial.c |   16 +++++-----------
>  1 files changed, 5 insertions(+), 11 deletions(-)
> ...
> -	/* Compute divisor value. Normally, we should simply return:
> -	 *   CFG_NS16550_CLK) / MODE_X_DIV / gd->baudrate
> -	 * but we need to round that value by adding 0.5 (2/4).
> -	 * Rounding is especially important at high baud rates.
> +	/*
> +	 * Compute divisor value, rounding it properly.  Rounding is
> +	 * especially important at high baud rates.
>  	 */

Please keep the comments explaining the base formula: it is not easy to reverse-engineer an optimized formula to figure out what is the base formula.

I will resubmit a patch with your fix and my comments.

Hugo V.