* [U-Boot-Users] [PATCH] ColdFire: Fix UART baudrate formula
@ 2008-05-29 17:29 Tsi-Chung.Liew
2008-05-29 17:37 ` Jerry Van Baren
0 siblings, 1 reply; 5+ messages in thread
From: Tsi-Chung.Liew @ 2008-05-29 17:29 UTC (permalink / raw)
To: u-boot
From: TsiChung Liew <Tsi-Chung.Liew@freescale.com>
Replace counter = bus_clk / (baudrate * 32) with
counter = ((bus_clk / 32) + (baudrate /2 )) / baudrate
formula
Signed-off-by: TsiChung Liew <Tsi-Chung.Liew@freescale.com>
---
drivers/serial/mcfuart.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/serial/mcfuart.c b/drivers/serial/mcfuart.c
index 88f3eb1..75e85b7 100644
--- a/drivers/serial/mcfuart.c
+++ b/drivers/serial/mcfuart.c
@@ -63,8 +63,8 @@ int serial_init(void)
uart->umr = UART_UMR_SB_STOP_BITS_1;
/* Setting up BaudRate */
- counter = (u32) (gd->bus_clk / (gd->baudrate));
- counter >>= 5;
+ counter = (u32) (gd->bus_clk / 32) + (gd->baudrate / 2));
+ counter = counter / gd->baudrate;
/* write to CTUR: divide counter upper byte */
uart->ubg1 = (u8) ((counter & 0xff00) >> 8);
--
1.5.4.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [U-Boot-Users] [PATCH] ColdFire: Fix UART baudrate formula
2008-05-29 17:29 Tsi-Chung.Liew
@ 2008-05-29 17:37 ` Jerry Van Baren
0 siblings, 0 replies; 5+ messages in thread
From: Jerry Van Baren @ 2008-05-29 17:37 UTC (permalink / raw)
To: u-boot
Tsi-Chung.Liew wrote:
> From: TsiChung Liew <Tsi-Chung.Liew@freescale.com>
>
> Replace counter = bus_clk / (baudrate * 32) with
> counter = ((bus_clk / 32) + (baudrate /2 )) / baudrate
> formula
I assume it works. :-)
Your comment is a duplicate of the code. A better comment would tell
the reader *why* you made the change. Suggestion...
The formula "counter = (u32) (gd->bus_clk / (gd->baudrate)) / 32" can
generate the wrong divisor due to integer division truncation. Round
the calculated divisor value by adding 1/2 the baudrate before dividing
by the baudrate.
Acked-by: Gerald Van Baren <vanbaren@cideas.com>
> Signed-off-by: TsiChung Liew <Tsi-Chung.Liew@freescale.com>
> ---
> drivers/serial/mcfuart.c | 4 ++--
> 1 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/serial/mcfuart.c b/drivers/serial/mcfuart.c
> index 88f3eb1..75e85b7 100644
> --- a/drivers/serial/mcfuart.c
> +++ b/drivers/serial/mcfuart.c
> @@ -63,8 +63,8 @@ int serial_init(void)
> uart->umr = UART_UMR_SB_STOP_BITS_1;
>
> /* Setting up BaudRate */
> - counter = (u32) (gd->bus_clk / (gd->baudrate));
> - counter >>= 5;
> + counter = (u32) (gd->bus_clk / 32) + (gd->baudrate / 2));
> + counter = counter / gd->baudrate;
>
> /* write to CTUR: divide counter upper byte */
> uart->ubg1 = (u8) ((counter & 0xff00) >> 8);
^ permalink raw reply [flat|nested] 5+ messages in thread
* [U-Boot-Users] [PATCH] ColdFire: Fix UART baudrate formula
@ 2008-05-29 20:26 Tsi-Chung.Liew
2008-05-29 20:59 ` Kenneth Johansson
0 siblings, 1 reply; 5+ messages in thread
From: Tsi-Chung.Liew @ 2008-05-29 20:26 UTC (permalink / raw)
To: u-boot
From: TsiChung Liew <Tsi-Chung.Liew@freescale.com>
The formula "counter = (u32) (gd->bus_clk / gd->baudrate) / 32"
can generate the wrong divisor due to integer division truncation.
Round the calculated divisor value by adding 1/2 the baudrate
before dividing by the baudrate.
Signed-off-by: TsiChung Liew <Tsi-Chung.Liew@freescale.com>
Acked-by: Gerald Van Baren <vanbaren@cideas.com>
---
drivers/serial/mcfuart.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/serial/mcfuart.c b/drivers/serial/mcfuart.c
index 88f3eb1..75e85b7 100644
--- a/drivers/serial/mcfuart.c
+++ b/drivers/serial/mcfuart.c
@@ -63,8 +63,8 @@ int serial_init(void)
uart->umr = UART_UMR_SB_STOP_BITS_1;
/* Setting up BaudRate */
- counter = (u32) (gd->bus_clk / (gd->baudrate));
- counter >>= 5;
+ counter = (u32) (gd->bus_clk / 32) + (gd->baudrate / 2));
+ counter = counter / gd->baudrate;
/* write to CTUR: divide counter upper byte */
uart->ubg1 = (u8) ((counter & 0xff00) >> 8);
--
1.5.4.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [U-Boot-Users] [PATCH] ColdFire: Fix UART baudrate formula
2008-05-29 20:26 [U-Boot-Users] [PATCH] ColdFire: Fix UART baudrate formula Tsi-Chung.Liew
@ 2008-05-29 20:59 ` Kenneth Johansson
0 siblings, 0 replies; 5+ messages in thread
From: Kenneth Johansson @ 2008-05-29 20:59 UTC (permalink / raw)
To: u-boot
On Thu, 2008-05-29 at 15:26 -0500, Tsi-Chung.Liew wrote:
> From: TsiChung Liew <Tsi-Chung.Liew@freescale.com>
>
> The formula "counter = (u32) (gd->bus_clk / gd->baudrate) / 32"
> can generate the wrong divisor due to integer division truncation.
> Round the calculated divisor value by adding 1/2 the baudrate
> before dividing by the baudrate.
>
> Signed-off-by: TsiChung Liew <Tsi-Chung.Liew@freescale.com>
> Acked-by: Gerald Van Baren <vanbaren@cideas.com>
> ---
> drivers/serial/mcfuart.c | 4 ++--
> 1 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/serial/mcfuart.c b/drivers/serial/mcfuart.c
> index 88f3eb1..75e85b7 100644
> --- a/drivers/serial/mcfuart.c
> +++ b/drivers/serial/mcfuart.c
> @@ -63,8 +63,8 @@ int serial_init(void)
> uart->umr = UART_UMR_SB_STOP_BITS_1;
>
> /* Setting up BaudRate */
> - counter = (u32) (gd->bus_clk / (gd->baudrate));
> - counter >>= 5;
> + counter = (u32) (gd->bus_clk / 32) + (gd->baudrate / 2));
And you compiled this ??
> + counter = counter / gd->baudrate;
>
> /* write to CTUR: divide counter upper byte */
> uart->ubg1 = (u8) ((counter & 0xff00) >> 8);
^ permalink raw reply [flat|nested] 5+ messages in thread
* [U-Boot-Users] [PATCH] ColdFire: Fix UART baudrate formula
@ 2008-05-29 22:20 Tsi-Chung.Liew
0 siblings, 0 replies; 5+ messages in thread
From: Tsi-Chung.Liew @ 2008-05-29 22:20 UTC (permalink / raw)
To: u-boot
From: TsiChung Liew <Tsi-Chung.Liew@freescale.com>
The formula "counter = (u32) (gd->bus_clk / gd->baudrate) / 32"
can generate the wrong divisor due to integer division truncation.
Round the calculated divisor value by adding 1/2 the baudrate
before dividing by the baudrate.
Signed-off-by: TsiChung Liew <Tsi-Chung.Liew@freescale.com>
Acked-by: Gerald Van Baren <vanbaren@cideas.com>
---
drivers/serial/mcfuart.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/serial/mcfuart.c b/drivers/serial/mcfuart.c
index 88f3eb1..5eb4f45 100644
--- a/drivers/serial/mcfuart.c
+++ b/drivers/serial/mcfuart.c
@@ -63,8 +63,8 @@ int serial_init(void)
uart->umr = UART_UMR_SB_STOP_BITS_1;
/* Setting up BaudRate */
- counter = (u32) (gd->bus_clk / (gd->baudrate));
- counter >>= 5;
+ counter = (u32) ((gd->bus_clk / 32) + (gd->baudrate / 2));
+ counter = counter / gd->baudrate;
/* write to CTUR: divide counter upper byte */
uart->ubg1 = (u8) ((counter & 0xff00) >> 8);
--
1.5.4.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
end of thread, other threads:[~2008-05-29 22:20 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2008-05-29 20:26 [U-Boot-Users] [PATCH] ColdFire: Fix UART baudrate formula Tsi-Chung.Liew
2008-05-29 20:59 ` Kenneth Johansson
-- strict thread matches above, loose matches on Subject: below --
2008-05-29 22:20 Tsi-Chung.Liew
2008-05-29 17:29 Tsi-Chung.Liew
2008-05-29 17:37 ` Jerry Van Baren
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox