[serial] Add general abstraction of a 16550-compatible UART

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/core/uart.c

@@ -0,0 +1,135 @@
+/*
+ * Copyright (C) 2014 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * 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; either version 2 of the
+ * License, or any later version.
+ *
+ * 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 Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ *
+ * You can also choose to distribute this program under the terms of
+ * the Unmodified Binary Distribution Licence (as given in the file
+ * COPYING.UBDL), provided that you have satisfied its requirements.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+/** @file
+ *
+ * 16550-compatible UART
+ *
+ */
+
+#include <unistd.h>
+#include <errno.h>
+#include <ipxe/uart.h>
+
+/** Timeout for transmit holding register to become empty */
+#define UART_THRE_TIMEOUT_MS 100
+
+/** Timeout for transmitter to become empty */
+#define UART_TEMT_TIMEOUT_MS 1000
+
+/**
+ * Transmit data
+ *
+ * @v uart		UART
+ * @v data		Data
+ */
+void uart_transmit ( struct uart *uart, uint8_t data ) {
+	unsigned int i;
+	uint8_t lsr;
+
+	/* Wait for transmitter holding register to become empty */
+	for ( i = 0 ; i < UART_THRE_TIMEOUT_MS ; i++ ) {
+		lsr = uart_read ( uart, UART_LSR );
+		if ( lsr & UART_LSR_THRE )
+			break;
+		mdelay ( 1 );
+	}
+
+	/* Transmit data (even if we timed out) */
+	uart_write ( uart, UART_THR, data );
+}
+
+/**
+ * Flush data
+ *
+ * @v uart		UART
+ */
+void uart_flush ( struct uart *uart ) {
+	unsigned int i;
+	uint8_t lsr;
+
+	/* Wait for transmitter and receiver to become empty */
+	for ( i = 0 ; i < UART_TEMT_TIMEOUT_MS ; i++ ) {
+		uart_read ( uart, UART_RBR );
+		lsr = uart_read ( uart, UART_LSR );
+		if ( ( lsr & UART_LSR_TEMT ) && ! ( lsr & UART_LSR_DR ) )
+			break;
+	}
+}
+
+/**
+ * Initialise UART
+ *
+ * @v uart		UART
+ * @v baud		Baud rate, or zero to leave unchanged
+ * @v lcr		Line control register value, or zero to leave unchanged
+ * @ret rc		Return status code
+ */
+int uart_init ( struct uart *uart, unsigned int baud, uint8_t lcr ) {
+	uint8_t dlm;
+	uint8_t dll;
+
+	/* Check for existence of UART */
+	if ( ! uart->base )
+		return -ENODEV;
+	uart_write ( uart, UART_SCR, 0x18 );
+	if ( uart_read ( uart, UART_SCR ) != 0x18 )
+		return -ENODEV;
+	uart_write ( uart, UART_SCR, 0xae );
+	if ( uart_read ( uart, UART_SCR ) != 0xae )
+		return -ENODEV;
+
+	/* Configure divisor and line control register, if applicable */
+	if ( ! lcr )
+		lcr = uart_read ( uart, UART_LCR );
+	uart->lcr = lcr;
+	uart_write ( uart, UART_LCR, ( lcr | UART_LCR_DLAB ) );
+	if ( baud ) {
+		uart->divisor = ( UART_MAX_BAUD / baud );
+		dlm = ( ( uart->divisor >> 8 ) & 0xff );
+		dll = ( ( uart->divisor >> 0 ) & 0xff );
+		uart_write ( uart, UART_DLM, dlm );
+		uart_write ( uart, UART_DLL, dll );
+	} else {
+		dlm = uart_read ( uart, UART_DLM );
+		dll = uart_read ( uart, UART_DLL );
+		uart->divisor = ( ( dlm << 8 ) | dll );
+	}
+	uart_write ( uart, UART_LCR, ( lcr & ~UART_LCR_DLAB ) );
+
+	/* Disable interrupts */
+	uart_write ( uart, UART_IER, 0 );
+
+	/* Enable FIFOs */
+	uart_write ( uart, UART_FCR, UART_FCR_FE );
+
+	/* Assert DTR and RTS */
+	uart_write ( uart, UART_MCR, ( UART_MCR_DTR | UART_MCR_RTS ) );
+
+	/* Flush any stale data */
+	uart_flush ( uart );
+
+	return 0;
+}