From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jerry Van Baren Date: Mon, 14 Jul 2008 22:44:03 -0400 Subject: [U-Boot-Users] [PATCH v2] Round the serial port clock divisor value returned by calc_divisor() In-Reply-To: <20080714210418.D979E242FD@gemini.denx.de> Message-ID: <20080715024403.GA5250@cideas.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de This formula is better at avoiding integer overflow. Signed-off-by: Gerald Van Baren --- 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. drivers/serial/serial.c | 16 +++++----------- 1 files changed, 5 insertions(+), 11 deletions(-) diff --git a/drivers/serial/serial.c b/drivers/serial/serial.c index 4ccaee2..7f43540 100644 --- a/drivers/serial/serial.c +++ b/drivers/serial/serial.c @@ -124,7 +124,6 @@ static NS16550_t serial_ports[4] = { static int calc_divisor (NS16550_t port) { - uint32_t clk_divisor; #ifdef CONFIG_OMAP1510 /* If can't cleanly clock 115200 set div to 1 */ @@ -147,17 +146,12 @@ static int calc_divisor (NS16550_t port) #define MODE_X_DIV 16 #endif - /* 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. */ - clk_divisor = (((4 * CFG_NS16550_CLK) / - (MODE_X_DIV * gd->baudrate)) + 2) / 4; - - debug("NS16550 clock divisor = %d\n", clk_divisor); - - return clk_divisor; + return (CFG_NS16550_CLK + (gd->baudrate * (MODE_X_DIV / 2))) / + (MODE_X_DIV * gd->baudrate); } #if !defined(CONFIG_SERIAL_MULTI) -- 1.5.6