From 3ee1668ab4fbf75b256ac8eef4273b1ea445c998 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Ky=C3=B6sti=20M=C3=A4lkki?= Date: Mon, 17 Feb 2014 19:37:52 +0200 Subject: uart8250: Fix and unify baudrate divisor calculation MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Divisor is a function of requested baudrate, platform-specific reference clock and amount of oversampling done on the UART reference. Calculate this parameter with divisor rounded to nearest integer. When building without option_table or when there is no entry for baud_rate, CONFIG_TTYS0_BAUD is used for default baudrate. For OxPCIe use of 4 MHz for reference was arbitrary giving correct divisor for 115200 but somewhat inaccurate for lower baudrates. Actual hardware is 62500000 with 16 times oversampling. FIXME: Field for baudrate in lb_tables is still incorrect. Change-Id: I68539738469af780fadd3392263dd9b3d5964d2d Signed-off-by: Kyösti Mälkki Reviewed-on: http://review.coreboot.org/5229 Tested-by: build bot (Jenkins) Reviewed-by: Stefan Reinauer --- src/drivers/uart/Makefile.inc | 6 ++++++ src/drivers/uart/util.c | 48 +++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 54 insertions(+) create mode 100644 src/drivers/uart/Makefile.inc create mode 100644 src/drivers/uart/util.c (limited to 'src/drivers/uart') diff --git a/src/drivers/uart/Makefile.inc b/src/drivers/uart/Makefile.inc new file mode 100644 index 0000000000..c797d4b44d --- /dev/null +++ b/src/drivers/uart/Makefile.inc @@ -0,0 +1,6 @@ +ifeq ($(CONFIG_CONSOLE_SERIAL),y) +romstage-y += util.c +ramstage-y += util.c +bootblock-y += util.c +smm-y += util.c +endif diff --git a/src/drivers/uart/util.c b/src/drivers/uart/util.c new file mode 100644 index 0000000000..c577048fb5 --- /dev/null +++ b/src/drivers/uart/util.c @@ -0,0 +1,48 @@ +/* + * This file is part of the coreboot project. + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; version 2 of the License. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA + */ + +#include +#include +#if CONFIG_USE_OPTION_TABLE +#include +#include "option_table.h" +#endif + +unsigned int default_baudrate(void) +{ +#if !defined(__SMM__) && CONFIG_USE_OPTION_TABLE + static const unsigned baud[8] = + { 115200, 57600, 38400, 19200, 9600, 4800, 2400, 1200 }; + unsigned b_index = 0; +#if defined(__PRE_RAM__) + b_index = read_option(baud_rate, 0xff); +#else + if (get_option(&b_index, "baud_rate") != CB_SUCCESS) + b_index = 0xff; +#endif + if (b_index < 8) + return baud[b_index]; +#endif + return CONFIG_TTYS0_BAUD; +} + +/* Calculate divisor. Do not floor but round to nearest integer. */ +unsigned int uart_baudrate_divisor(unsigned int baudrate, + unsigned int refclk, unsigned int oversample) +{ + return (1 + (2 * refclk) / (baudrate * oversample)) / 2; +} -- cgit v1.2.3