Jerry Van Baren wrote:
Hugo Villeneuve wrote:
Round the serial port clock divisor value returned by calc_divisor().
Signed-off-by: Hugo Villeneuve hugo.villeneuve@lyrtech.com
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 | 7 ++++++- 1 files changed, 6 insertions(+), 1 deletions(-)
diff --git a/drivers/serial/serial.c b/drivers/serial/serial.c index 76425d8..7e315ad 100644 --- a/drivers/serial/serial.c +++ b/drivers/serial/serial.c @@ -124,6 +124,8 @@ static NS16550_t serial_ports[4] = {
static int calc_divisor (NS16550_t port) {
- u32 divisor_x10;
#ifdef CONFIG_OMAP1510 /* If can't cleanly clock 115200 set div to 1 */ if ((CFG_NS16550_CLK == 12000000) && (gd->baudrate == 115200)) { @@ -144,8 +146,11 @@ 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 with rounding by adding 0.5 */
- divisor_x10 = (10 * CFG_NS16550_CLK) / MODE_X_DIV / gd->baudrate; +
- return (divisor_x10 + 5) / 10;
}
#if !defined(CONFIG_SERIAL_MULTI)
Hi Hugo,
Will a real rounding work? Work better? If I got my mental math and parenthesis right and the resulting math doesn't overflow your registers, the following will add 1/2 the baud rate scaled by the MODE_X_DIV and then perform the divide which will do full rounding.
return (((CFG_NS16550_CLK + ((gd->baudrate / 2)* MODE_X_DIV)) / MODE_X_DIV) / gd->baudrate);
I tested it and it works for me. But maybe the code is less obvious that way?
Alternately, I prefer to scale up by 16 and then divide by 8 since processors can do that very efficiently ( << 4 followed by >> 3).
Right.
I prefer the second solution for its simplicity, but the first one also works.
Hugo.
Hugo Villeneuve Hardware developer | Concepteur matériel Lyrtech Phone/Tél. : (1) (418) 877-4644 #2395 Toll-free/Sans frais - Canada & USA : (1) (888) 922-4644 #2395 Fax/Téléc. : (1) (418) 877-7710 www.lyrtech.com Infinite possibilities...TM