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

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

[Jerry Van Baren]

This formula is better at avoiding integer overflow.

Signed-off-by: Gerald Van Baren <vanbaren@cideas.com>
---

(try 2)

The formula I proposed previously in this thread compiles OK.  I cannot
verify it is correct on real hardware, however.
<http://thread.gmane.org/gmane.comp.boot-loaders.u-boot/43499/focus=43506>

Best regards,
gvb 

 drivers/serial/serial.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/drivers/serial/serial.c b/drivers/serial/serial.c
index 182ca2d..48579ae 100644
--- a/drivers/serial/serial.c
+++ b/drivers/serial/serial.c
@@ -150,7 +150,9 @@ static int calc_divisor (NS16550_t port)
 	 * but we need to round that value by adding 0.5 or 8/16.
 	 * Rounding is especially important at high baud rates.
 	 */
-	return (((16 * CFG_NS16550_CLK) / MODE_X_DIV / gd->baudrate) + 8) / 16;
+	return (CFG_NS16550_CLK + (gd->baudrate / 2)) /
+		(MODE_X_DIV * gd->baudrate);
+
 }
 
 #if !defined(CONFIG_SERIAL_MULTI)
-- 
1.5.6

[U-Boot-Users] [PATCH] 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.

This patch doesn?t round the value correctly.

Wolfgang, I will resubmit a new patch shortly today to fix the problem.

Hugo V.

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

[Jerry Van Baren]

Hugo Villeneuve wrote:
> u-boot-users-bounces at lists.sourceforge.net wrote:
>> This formula is better at avoiding integer overflow.
> 
> This patch doesn?t round the value correctly.
> 
> Wolfgang, I will resubmit a new patch shortly today to fix the problem.
> 
> Hugo V.

Arrgh, you are right.  I know you solved it already, but for the record 
I oversimplified:
   (gd->baudrate / 2)
should have been:
   (gd->baudrate * (MODE_X_DIV / 2))

WRONG:
+	return (CFG_NS16550_CLK + (gd->baudrate / 2)) /
+		(MODE_X_DIV * gd->baudrate);

should have been
+	return (CFG_NS16550_CLK + (gd->baudrate * (MODE_X_DIV / 2))) /
+		(MODE_X_DIV * gd->baudrate);

Sorry,
gvb