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/include/uart.h | 17 +++++++++++++++++ src/include/uart8250.h | 4 ---- 2 files changed, 17 insertions(+), 4 deletions(-) (limited to 'src/include') diff --git a/src/include/uart.h b/src/include/uart.h index b520e09bdb..997fe185ce 100644 --- a/src/include/uart.h +++ b/src/include/uart.h @@ -20,6 +20,23 @@ #ifndef UART_H #define UART_H +/* Return the clock frequency UART uses as reference clock for + * baudrate generator. */ +unsigned int uart_platform_refclk(void); + +/* Return the baudrate determined from option_table, or when that is + * not used, CONFIG_TTYS0_BAUD. + */ +unsigned int default_baudrate(void); + +/* Returns the divisor value for a given baudrate. + * The formula to satisfy is: + * refclk / divisor = baudrate * oversample + */ +unsigned int uart_baudrate_divisor(unsigned int baudrate, + unsigned int refclk, unsigned int oversample); + + unsigned char uart_rx_byte(void); void uart_tx_byte(unsigned char data); void uart_tx_flush(void); diff --git a/src/include/uart8250.h b/src/include/uart8250.h index a48c948138..112cd44945 100644 --- a/src/include/uart8250.h +++ b/src/include/uart8250.h @@ -105,10 +105,6 @@ #define UART_SCR 0x07 #define UART_SPR 0x07 -#if ((115200 % CONFIG_TTYS0_BAUD) != 0) -#error Bad ttyS0 baud rate -#endif - #if CONFIG_CONSOLE_SERIAL8250 unsigned char uart8250_rx_byte(unsigned base_port); int uart8250_can_rx_byte(unsigned base_port); -- cgit v1.2.3