Wolfgang Denk wrote:
In message <[EMAIL PROTECTED]> you wrote:
Round the serial port clock divisor value returned by
calc_divisor().
Signed-off-by: Hugo Villeneuve <[EMAIL PROTECTED]>
Signed-off-by: John Roberts <[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 | 6 +++++-
1 files changed, 5 insertions(+), 1 deletions(-)
diff --git a/drivers/serial/serial.c b/drivers/serial/serial.c
index 76425d8..1192f07 100644
--- a/drivers/serial/serial.c
+++ b/drivers/serial/serial.c
@@ -144,8 +144,12 @@ 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. Normally, we should simply return:
+ * CFG_NS16550_CLK) / MODE_X_DIV / gd->baudrate
+ * 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;
}
Your patch causes problems with some boards:
Configuring for SBC8540 board...
serial.c: In function 'calc_divisor':
serial.c:153: warning: integer overflow in expression
serial.c:153: warning: integer overflow in expression
Configuring for sbc8548 board...
serial.c: In function 'calc_divisor':
serial.c:153: warning: integer overflow in expression
serial.c:153: warning: integer overflow in expression
Do you have a quick fix, or shall I back out the patch?
Best regards,
Wolfgang Denk
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>
My apologies for providing the patch as an attachment. I need to add
the external editor plugin so I can use tbird for proper inline patches.
Best regards,
gvb
>From 97b1ea8273eec4e45df71e074e0790d39fd6536d Mon Sep 17 00:00:00 2001
From: Gerald Van Baren <[EMAIL PROTECTED]>
Date: Thu, 10 Jul 2008 19:44:28 -0400
Subject: [PATCH] Round the serial port clock divisor value returned by calc_divisor()
This algorithm is better at avoiding integer overflow.
Signed-off-by: Gerald Van Baren <[EMAIL PROTECTED]>
---
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
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