src/lib/uart8250.c

/*
 * This file is part of the coreboot project.
 *
 * Copyright (C) 2003 Eric Biederman
 * Copyright (C) 2006-2010 coresystems GmbH
 *
 * 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 <arch/io.h>
#include <console/uart.h>
#include <uart8250.h>
#include <trace.h>

/* Should support 8250, 16450, 16550, 16550A type UARTs */

/* Nominal values only, good for the range of choices Kconfig offers for
 * set of standard baudrates.
 */
#define BAUDRATE_REFCLK		(115200)
#define BAUDRATE_OVERSAMPLE	(1)

/* Expected character delay at 1200bps is 9ms for a working UART
 * and no flow-control. Assume UART as stuck if shift register
 * or FIFO takes more than 50ms per character to appear empty.
 *
 * Estimated that inb() from UART takes 1 microsecond.
 */
#define SINGLE_CHAR_TIMEOUT	(50 * 1000)
#define FIFO_TIMEOUT		(16 * SINGLE_CHAR_TIMEOUT)

static inline int uart8250_can_tx_byte(unsigned base_port)
{
	return inb(base_port + UART_LSR) & UART_LSR_THRE;
}

static inline void uart8250_wait_to_tx_byte(unsigned base_port)
{
	unsigned long int i = SINGLE_CHAR_TIMEOUT;
	while (i-- && !uart8250_can_tx_byte(base_port));
}

static inline void uart8250_wait_until_sent(unsigned base_port)
{
	unsigned long int i = FIFO_TIMEOUT;
	while (i-- && !(inb(base_port + UART_LSR) & UART_LSR_TEMT));
}

void uart8250_tx_byte(unsigned base_port, unsigned char data)
{
	uart8250_wait_to_tx_byte(base_port);
	outb(data, base_port + UART_TBR);
}

void uart8250_tx_flush(unsigned base_port)
{
	uart8250_wait_until_sent(base_port);
}

int uart8250_can_rx_byte(unsigned base_port)
{
	return inb(base_port + UART_LSR) & UART_LSR_DR;
}

unsigned char uart8250_rx_byte(unsigned base_port)
{
	unsigned long int i = SINGLE_CHAR_TIMEOUT;
	while (i-- && !uart8250_can_rx_byte(base_port));

	if (i)
		return inb(base_port + UART_RBR);
	else
		return 0x0;
}

void uart8250_init(unsigned base_port, unsigned divisor)
{
	DISABLE_TRACE;
	/* Disable interrupts */
	outb(0x0, base_port + UART_IER);
	/* Enable FIFOs */
	outb(UART_FCR_FIFO_EN, base_port + UART_FCR);

	/* assert DTR and RTS so the other end is happy */
	outb(UART_MCR_DTR | UART_MCR_RTS, base_port + UART_MCR);

	/* DLAB on */
	outb(UART_LCR_DLAB | CONFIG_TTYS0_LCS, base_port + UART_LCR);

	/* Set Baud Rate Divisor. 12 ==> 9600 Baud */
	outb(divisor & 0xFF,   base_port + UART_DLL);
	outb((divisor >> 8) & 0xFF,    base_port + UART_DLM);

	/* Set to 3 for 8N1 */
	outb(CONFIG_TTYS0_LCS, base_port + UART_LCR);
	ENABLE_TRACE;
}

void uart_init(void)
{
	unsigned int div;
	div = uart_baudrate_divisor(default_baudrate(), BAUDRATE_REFCLK,
		BAUDRATE_OVERSAMPLE);
	uart8250_init(CONFIG_TTYS0_BASE, div);
}