Submitted by: Bill Paul (wpaul@ctr.columbia.edu)

Obtained from:
bios boot block changed to allow booting from both the attached graphics
display and from a serial port. (A specially compiled serial boot block
is no longer necessary.) The boot block should detect the presence or
absence of a keyboard: if there is no keyboard, COM1 is turned into the
console. This simulates the behavior of the Sun boot PROMs. Unplug your
keyboard, attach a terminal to COM1 and you should be ready to go. :)

6 files changed, 472 insertions, 54 deletions

diff --git a/sys/i386/boot/biosboot/Makefile b/sys/i386/boot/biosboot/Makefile
index d147e75..ed1ab3a 100644
--- a/sys/i386/boot/biosboot/Makefile
+++ b/sys/i386/boot/biosboot/Makefile
@@ -1,15 +1,16 @@
-#	$Id: Makefile,v 1.22 1994/11/05 21:06:16 ache Exp $
+#	$Id: Makefile,v 1.23 1994/12/18 19:14:08 bde Exp $
 #
 
 PROG=	boot
 # Order is very important on the SRCS line for this prog
-SRCS=	start.S table.c boot2.S boot.c asm.S bios.S io.c disk.c sys.c
+SRCS=	start.S table.c boot2.S boot.c asm.S bios.S serial.S
+SRCS+=  probe_keyboard.c io.c disk.c sys.c
 
 BINDIR=		/usr/mdec
 BINMODE=	444
-CFLAGS=		-O -DDO_BAD144 -DBOOTWAIT=${BOOTWAIT}
+CFLAGS=		-O2 -DDO_BAD144 -DBOOTWAIT=${BOOTWAIT} -DCOMCONSOLE=0x3F8
 CFLAGS+=	-DBOOTSEG=${BOOTSEG} -DBOOTSTACK=${BOOTSTACK}
-CFLAGS+=	-I${.CURDIR} -I${.CURDIR}/../..
+CFLAGS+=	-I${.CURDIR} -I${.CURDIR}/../.. -DRB_SERIAL=0x1000
 CLEANFILES+=	boot.nohdr boot.strip boot1 boot2
 DPADD=		${LIBC}
 LDFLAGS+=	-N -T 0 -nostdlib
diff --git a/sys/i386/boot/biosboot/README.serial b/sys/i386/boot/biosboot/README.serial
new file mode 100644
index 0000000..c4c34dc
--- /dev/null
+++ b/sys/i386/boot/biosboot/README.serial
@@ -0,0 +1,132 @@
+	$Id$
+                         SERIAL CONSOLE USAGE NOTES
+                      Bill Paul (wpaul@ctr.columbia.edu)
+
+The FreeBSD boot block can now be used to boot FreeBSD on a system with
+only a dumb terminal on a serial port (COM1) as a console. This feature
+is provided for the benefit of people who wish to install FreeBSD on
+dedicated file/compute/terminal server machines that have no keyboard
+(or monitor) attached, just as is possible with Sun workstations and
+servers. People who don't need this extra functionality shouldn't notice
+the changes at all (unless I've screwed something up horribly).
+
+Note that 'options COMCONSOLE' can still be used to force the kernel to
+boot in 'serial console' mode regardless of what boot options you use.
+
+To boot FreeBSD in serial console mode, you must to the following:
+
+- Unplug your keyboard. Most PC systems probe for the keyboard during the
+  Power-On Self-Test (POST) and will generate an error if the keyboard
+  isn't detected. Additionally, many machines will pause the boot process
+  and wait for you to reattach the keyboard and press a key before
+  proceeding any further. If your computer complains about the lack of a
+  keyboard but boots anyway, then you don't have to do anything special.
+  (One machine with a PHOENIX BIOS that I have here merely says 'Keyboard
+  failed' then continues to boot normally.) If your machine complains
+  loudly about the lack of a keyboard and won't continue to boot until you
+  plug it back in, you'll have to go into your CMOS configuration menu and
+  change the 'Keyboard' setting to 'Not installed' in order to bypass the
+  keyboard probe.
+
+  NOTE: Setting the keyboard to 'Not installed' in the CMOS configuration
+  does *NOT* mean that you won't be able to use your keyboard. All this 
+  does is tell the BIOS not to probe for a keyboard at power-on so that
+  it won't bitch and moan if the keyboard isn't plugged in. You can leave the
+  keyboard plugged in even with this flag set to 'Not installed' and the
+  keyboard will still work. I repeat: changing the CMOS 'keyboard' setting
+  to 'Not installed' only disables the BIOS's keyboard probe; it does 
+  *NOT* actually disable the keyboard.
+
+- Plug a dumb terminal into COM1. If you don't have a dumb terminal, you
+  can use an old PC/XT with a modem program, or the serial port on
+  another UNIX box. If you don't have a COM1, get one. At this time,
+  there is no way to select a port other than COM1 without recompiling
+  both the kernel and the boot blocks. If you're already using COM1 for
+  another device, you'll have to temporarily remove that device and
+  install a new boot block and kernel once you get FreeBSD up and running.
+  (It is assumed that COM1 will be available on a file/compute/terminal
+  server anyway; if you really need COM1 for something else (and you can't
+  switch it to COM2), then you probably shouldn't even be bothering with
+  all this.)
+
+  The serial port settings are hardcoded to 9600 baud, 8 bits, no parity,
+  1 stop bit.
+
+  NOTE: in addition to a serial cable, you will need a null modem adapter
+  in order to connect the terminal to the PC's serial port. If you don't
+  have one, go to Radio Shack and buy one: they're cheap.
+
+- Boot the machine. The boot block will probe for a keyboard on your
+  system. If it fails to find one, you'll see a prompt appear on the
+  terminal that looks like this:
+
+  No keyboard found.
+
+  >> FreeBSD BOOT @ 0x10000: 640/7168 k of memory
+  Use hd(1,a)/kernel to boot sd0 when wd0 is also installed.
+  Usage: [[[fd(0,a)]/kernel][-s][-r][-a][-c][-d][-b][-v][-h]]
+  Use ? for file list or simply press Return for defaults
+  Boot:
+
+  This is identical to the prompt that normally appears on the VGA console,
+  except for the 'No keyboard found' message that indicates a keyboard
+  couldn't be detected. (If a keyboard is detected, the boot prompt will
+  appear on the VGA display as usual.)
+
+  From here you can boot the system (or let it autoboot by itself) just
+  like you can from the VGA console and the kernel will automatically
+  use COM1 as the console device. No recompilation or 'options COMCONSOLE'
+  is required. This is done by passing a special flag to the kernel in
+  the 'boothowto' word. (The curious can refer to <sys/reboot.h> and the
+  sio driver sources for details.)
+
+- You will notice that there's a new boot flag: -h. You can use this to
+  force the kernel to switch console devices. For instance, if you boot
+  from the VGA console, you can use -h to force the kernel to use the
+  serial port as its console device. Alternatively, if you boot from
+  the serial port, using -h will force the kernel to use the VGA display
+  as the console instead. (Can you say 'toggle' boys and girls? I knew
+  you could. Now try saying 'XOR.')
+
+CAVEATS:
+
+- The idea here is to allow people to set up dedicated servers that require
+  no graphics hardware or attached keyboards. Unfortunately, while (most?)
+  every system will let you boot without a keyboard, there are quite a few
+  that will not let you boot without a graphics adapter. Machines with
+  AMI BIOSes can be configured to boot with no graphics adapter installed
+  simply by changing the 'graphics adapter' setting in the CMOS configuration
+  to 'Not installed.' However, many machines do not support this option
+  and will refuse to boot if you have no display hardware installed. With
+  these machines, you'll have to leave some kind of graphics card installed,
+  (even if it's just a junky mono board) although you won't have to plug a
+  monitor into it. You might also try installing an AMI BIOS. :)
+
+- Using a port other than COM1 as the console requires some recompiling.
+  Again, it's usually assumed that COM1 will be available for use as a
+  console device on a dedicated file/compute/terminal server, so hopefully
+  you'll never have to do this. But if you feel you must change the console
+  to a different port, here's how:
+
+	o Get the kerndist kernel source package.
+	o Edit /sys/i386/boot/biosboot/Makefile and set COMCONSOLE to the
+	  address of the port you want to use (0x3F8, 0x2E8, 0x3E8 or
+	  0x2E8). Only COM1 through COM4 can be used; multiport serial
+	  cards will not work. No interrupt setting is needed.
+	o Create a custom kernel configuration file and add the following
+	  lines:
+
+	  options "CONADDR=0x3F8"
+	  options "CONUNIT=0"
+
+	  Set CONADDR to the same address that you selected for COMCONSOLE
+	  in the bootbios Makefile. Set CONUNIT to the unit number of the
+	  serial port that this address corresponds to (0 = sio0, 1 = sio1,
+	  etc). This implies that the serial port you want to use must be
+	  configured into the kernel in the normal way first. I'm not
+	  going to list all the possible combinations here; just use your
+	  head and you should be okay.
+	o Recompile both the boot blocks and the kernel.
+	o Install the boot blocks with the disklabel command and boot
+	  from the new kernel.
+
diff --git a/sys/i386/boot/biosboot/boot.c b/sys/i386/boot/biosboot/boot.c
index 290ec31..a9a31ee 100644
--- a/sys/i386/boot/biosboot/boot.c
+++ b/sys/i386/boot/biosboot/boot.c
@@ -24,7 +24,7 @@
  * the rights to redistribute these changes.
  *
  *	from: Mach, [92/04/03  16:51:14  rvb]
- *	$Id: boot.c,v 1.28 1994/12/18 19:14:13 bde Exp $
+ *	$Id: boot.c,v 1.29 1994/12/18 20:30:10 joerg Exp $
  */
 
 
@@ -59,52 +59,47 @@ WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 
 struct exec head;
 struct bootinfo_t bootinfo;
-char *name;
-char *names[] = {
-	"/kernel"
-};
-#define NUMNAMES	(sizeof(names)/sizeof(char *))
+char *name = { "/kernel" };
 
-#ifdef COMCONSOLE
 extern void init_serial(void);
-#endif
+extern int probe_keyboard(void);
+int loadflags = 0;
 
 extern int end;
 boot(drive)
 int drive;
 {
-	int loadflags, currname = 0, ret;
+	int ret;
 	char *t;
-#ifdef COMCONSOLE
-	init_serial();
-#endif
 
-		
+	if (probe_keyboard()) {
+		init_serial();
+		loadflags |= RB_SERIAL;
+		printf ("\nNo keyboard found.\n");
+	}
+
 	/* Pick up the story from the Bios on geometry of disks */
 
 	for(ret = 0; ret < N_BIOS_GEOM; ret ++)
 		bootinfo.bios_geom[ret] = get_diskinfo(ret + 0x80);
 
-	printf("\n>> FreeBSD BOOT @ 0x%x: %d/%d k of memory\n",
-		ouraddr, memsize(0), memsize(1));
-	printf("Use hd(1,a)/kernel to boot sd0 when wd0 is also installed.\n");
-	printf("Usage: [[[%s(0,a)]%s][-s][-r][-a][-c][-d][-b][-v]]\n",
-			devs[(drive & 0x80) ? 0 : 2], names[0]);
-	printf("Use ? for file list or simply press Return for defaults\n");
+	/* This is nasty, but why use 4 printf()s when 1 will do. */
+
+	printf("\n>> FreeBSD BOOT @ 0x%x: %d/%d k of memory\nUse hd(1,a)/kernel to boot sd0 when wd0 is also installed.\nUsage: [[[%s(%d,a)]%s][-s][-r][-a][-c][-d][-b][-v][-h]]\nUse ? for file list or simply press Return for defaults\n", ouraddr, memsize(0), memsize(1), devs[(drive & 0x80) ? 0 : 2],
+	(unit = (drive & 0x7f)), name);
+
 	gateA20();
+
 loadstart:
 	/***************************************************************\
 	* As a default set it to the first partition of the first	*
 	* floppy or hard drive						*
 	\***************************************************************/
-	part = unit = 0;
+
+	part = 0;
 	maj = (drive&0x80 ? 0 : 2);		/* a good first bet */
-	name = names[currname++];
 
-	loadflags = 0;
-	if (currname == NUMNAMES)
-		currname = 0;
-	printf("Boot: ");
+	printf ("Boot: ");
 	getbootdev(&loadflags);
 	ret = openrd();
 	if (ret != 0) {
@@ -147,6 +142,12 @@ loadprog(howto)
 			, 'a'+part
 			, name
 			, addr);
+/*
+ * With the current scheme of things, addr can never be less than ouraddr,
+ * so this next bit of code is largely irrelevant. Taking it out saves lots
+ * of space.
+ */
+#ifdef REDUNDANT 
 	if(addr < ouraddr)
 	{
 		if((addr + head.a_text + head.a_data) > ouraddr)
@@ -160,6 +161,7 @@ loadprog(howto)
 			return;
 		}
 	}
+#endif
 	printf("text=0x%x ", head.a_text);
 	/********************************************************/
 	/* LOAD THE TEXT SEGMENT				*/
@@ -185,6 +187,11 @@ loadprog(howto)
 	/* (but clear it)					*/
 	/********************************************************/
 	printf("bss=0x%x ", head.a_bss);
+
+/*
+ * This doesn't do us any good anymore either.
+ */
+#ifdef REDUNDANT
 	if( (addr < ouraddr) && ((addr + head.a_bss) > ouraddr))
 	{
 		pbzero(addr,ouraddr - (int)addr);
@@ -194,7 +201,9 @@ loadprog(howto)
 		pbzero(addr,head.a_bss);
 	}
 	addr += head.a_bss;
-
+#else
+	pbzero(addr,head.a_bss);
+#endif
 #ifdef LOADSYMS /* not yet, haven't worked this out yet */
 	if (addr > 0x100000)
 	{
@@ -286,6 +295,8 @@ getbootdev(howto)
 						*howto |= RB_HALT; continue;
 					      case 'v':
 						*howto |= RB_VERBOSE; continue;
+					      case 'h':
+						*howto ^= RB_SERIAL; continue;
 					}
 			else {
 				name = ptr;
diff --git a/sys/i386/boot/biosboot/io.c b/sys/i386/boot/biosboot/io.c
index 25dc322..7932385 100644
--- a/sys/i386/boot/biosboot/io.c
+++ b/sys/i386/boot/biosboot/io.c
@@ -1,4 +1,3 @@
-
 /*
  * Mach Operating System
  * Copyright (c) 1992, 1991 Carnegie Mellon University
@@ -25,10 +24,11 @@
  * the rights to redistribute these changes.
  *
  *	from: Mach, Revision 2.2  92/04/04  11:35:57  rpd
- *	$Id: io.c,v 1.9 1994/09/20 22:24:59 adam Exp $
+ *	$Id: io.c,v 1.10 1994/11/07 11:26:29 davidg Exp $
  */
 
 #include <machine/cpufunc.h>
+#include <sys/reboot.h>
 
 #define K_RDWR 		0x60		/* keyboard data & cmds (read/write) */
 #define K_STATUS 	0x64		/* keyboard status */
@@ -44,6 +44,8 @@
 					   enable data line
 					   enable clock line */
 
+extern int loadflags;
+
 /*
  * Gate A20 for high memory
  */
@@ -73,7 +75,6 @@ printf(format,data)
 	int *dataptr = &data;
 	char c;
 
-	reset_twiddle();
 	while (c = *format++)
 		if (c != '%')
 			putchar(c);
@@ -119,9 +120,12 @@ printf(format,data)
 
 putchar(c)
 {
-	if (c == '\n')
-		putc('\r');
-	putc(c);
+	if (c == '\n') {
+		if (loadflags & RB_SERIAL) serial_putc('\r');
+			else putc('\r');
+	}
+	if (loadflags & RB_SERIAL) serial_putc(c);
+		else putc(c);
 }
 
 getchar(in_buf)
@@ -130,7 +134,7 @@ getchar(in_buf)
 	int c;
 
 loop:
-	if ((c=getc()) == '\r')
+	if ((c = ((loadflags & RB_SERIAL) ? serial_getc(c) : getc(c))) == '\r')
 		c = '\n';
 	if (c == '\b') {
 		if (in_buf != 0) {
@@ -173,7 +177,7 @@ char *buf;
 #if BOOTWAIT
 	for (i = BOOTWAIT; i>0; delay1ms(),i--)
 #endif
-		if (ischar())
+		if ((loadflags & RB_SERIAL) ? serial_ischar() : ischar())
 			for (;;)
 				switch(*ptr = getchar(ptr - buf) & 0xff) {
 				      case '\n':
@@ -186,6 +190,7 @@ char *buf;
 				      default:
 					ptr++;
 				}
+
 	return 0;
 }
 
@@ -208,24 +213,13 @@ int len;
 		*to++ = *from++;
 }
 
-static int tw_on;
-static int tw_pos;
-static char tw_chars[] = "|/-\\";
+/* To quote Ken: "You are not expected to understand this." :) */
 
-reset_twiddle()
-{
-	if (tw_on)
-		putchar('\b');
-	tw_on = 0;
-	tw_pos = 0;
-}
+static unsigned long tw_chars = 0x5C2D2F7C; /* "\-/|" */
 
 twiddle()
 {
-	if (tw_on)
-		putchar('\b');
-	else
-		tw_on = 1;
-	putchar(tw_chars[tw_pos++]);
-	tw_pos %= (sizeof(tw_chars) - 1);
+	putchar((char)tw_chars);
+	tw_chars = (tw_chars >> 8) | ((tw_chars & (unsigned long)0xFF) << 24);
+	putchar('\b');
 }
diff --git a/sys/i386/boot/biosboot/probe_keyboard.c b/sys/i386/boot/biosboot/probe_keyboard.c
new file mode 100644
index 0000000..694db14
--- /dev/null
+++ b/sys/i386/boot/biosboot/probe_keyboard.c
@@ -0,0 +1,82 @@
+/*-
+ * Copyright (c) 1992-1995 Søren Schmidt
+ * Copyright (c) 1990 The Regents of the University of California.
+ * All rights reserved.
+ *
+ * This code is derived from software contributed to Berkeley by
+ * William Jolitz and Don Ahn.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer
+ *    in this position and unchanged.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. All advertising materials mentioning features or use of this software
+ *    must display the following acknowledgement:
+ *	This product includes software developed by the University of
+ *	California, Berkeley and its contributors.
+ * 4. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * This is a modified version of the keyboard reset code used in syscons.
+ * If the keyboard reset fails, we assume that the keyboard has been
+ * unplugged and we use a serial port (COM1) as the console instead.
+ * Returns 1 on failure (no keyboard), 0 on success (keyboard attached).
+ *
+ * This grody hack brought to you by Bill Paul (wpaul@ctr.columbia.edu)
+ *
+ *	$Id$
+ */
+
+#include <machine/console.h>
+#include <machine/cpufunc.h>
+
+#ifdef BOOTWAIT
+extern int delay1ms(void);
+#else
+int delay1ms()
+{
+        int i = 800;
+        while (--i >= 0)
+                (void)inb(0x84);
+}
+#endif
+
+int
+probe_keyboard(void)
+{
+	int i, retries = 5;
+	unsigned char val;
+
+	/* Try to reset keyboard hardware */
+	while (retries--) {
+		outb(KB_DATA, KB_RESET);
+		for (i=0; i<100000; i++) {
+			delay1ms();
+			val = inb(KB_DATA);
+			if (val == KB_ACK || val == KB_ECHO)
+				return(0);	
+			if (val == KB_RESEND)
+				return (1);
+		}
+	}
+
+	return (0);
+}
diff --git a/sys/i386/boot/biosboot/serial.S b/sys/i386/boot/biosboot/serial.S
new file mode 100644
index 0000000..34d0528
--- /dev/null
+++ b/sys/i386/boot/biosboot/serial.S
@@ -0,0 +1,198 @@
+/*
+ * Mach Operating System
+ * Copyright (c) 1992, 1991 Carnegie Mellon University
+ * All Rights Reserved.
+ * 
+ * Permission to use, copy, modify and distribute this software and its
+ * documentation is hereby granted, provided that both the copyright
+ * notice and this permission notice appear in all copies of the
+ * software, derivative works or modified versions, and any portions
+ * thereof, and that both notices appear in supporting documentation.
+ * 
+ * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
+ * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
+ * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
+ * 
+ * Carnegie Mellon requests users of this software to return to
+ * 
+ *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
+ *  School of Computer Science
+ *  Carnegie Mellon University
+ *  Pittsburgh PA 15213-3890
+ * 
+ * any improvements or extensions that they make and grant Carnegie Mellon
+ * the rights to redistribute these changes.
+ *
+ *	from: Mach, Revision 2.2  92/04/04  11:34:26  rpd
+ *	$Id: bios.S,v 1.1 1994/12/18 20:12:08 joerg Exp $
+ */
+
+/*
+  Copyright 1988, 1989, 1990, 1991, 1992 
+   by Intel Corporation, Santa Clara, California.
+
+                All Rights Reserved
+
+Permission to use, copy, modify, and distribute this software and
+its documentation for any purpose and without fee is hereby
+granted, provided that the above copyright notice appears in all
+copies and that both the copyright notice and this permission notice
+appear in supporting documentation, and that the name of Intel
+not be used in advertising or publicity pertaining to distribution
+of the software without specific, written prior permission.
+
+INTEL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE
+INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS,
+IN NO EVENT SHALL INTEL BE LIABLE FOR ANY SPECIAL, INDIRECT, OR
+CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+LOSS OF USE, DATA OR PROFITS, WHETHER IN ACTION OF CONTRACT,
+NEGLIGENCE, OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
+WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+/*
+ * Serial bootblock interface routines
+ * Copyright (c) 1994, J"org Wunsch
+ *
+ * Permission to use, copy, modify and distribute this software and its
+ * documentation is hereby granted, provided that both the copyright
+ * notice and this permission notice appear in all copies of the
+ * software, derivative works or modified versions, and any portions
+ * thereof, and that both notices appear in supporting documentation.
+ *
+ * THE AUTHOR ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
+ * CONDITION.  THE AUTHOR DISCLAIMS ANY LIABILITY OF ANY KIND FOR
+ * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
+ */ 
+
+	.file	"serial.s"
+
+#include "asm.h"
+	.text
+
+/*
+ * The serial port interface routines implement a simple polled i/o
+ * interface to a standard serial port.  Due to the space restrictions
+ * for the boot blocks, no BIOS support is used (since BIOS requires
+ * expensive real/protected mode switches), instead the rudimentary
+ * BIOS support is duplicated here.
+ *
+ * The base address for the i/o port is passed from the Makefile in
+ * the COMCONSOLE preprocessor macro.  Console parameters are currently
+ * hard-coded to 9600 Bd, 8 bit.  This can be changed in the
+ * init_serial() function.
+ */
+
+/*
+ * void serial_putc(char ch)
+ *	send ch to serial port
+ *
+ */
+
+ENTRY(serial_putc)
+	push	%ebp
+	mov	%esp, %ebp
+	push	%edx
+
+	mov	$COMCONSOLE + 5, %edx	# line status reg
+1:	inb	%dx, %al
+	test	$0x20, %al
+	jz	1b		# TX buffer not empty
+
+	movb	0x8(%ebp), %al
+
+	sub	$5, %edx	# TX output reg
+	outb	%al, %dx	# send this one
+
+	pop	%edx
+	pop	%ebp
+	ret
+
+/*
+ * int serial_getc(void)
+ *	read a character from serial port
+ */
+
+ENTRY(serial_getc)
+	push	%ebp
+	mov	%esp, %ebp
+	push	%edx
+
+	mov	$COMCONSOLE + 5, %edx	# line status reg
+1:
+	inb	%dx, %al
+	testb	$0x01, %al
+	jz	1b		# no RX char available
+
+	xor	%eax, %eax
+	sub	$5, %edx	# RX buffer reg
+	inb	%dx, %al	# fetch (first) character
+
+	cmp	$0x7F, %eax	# make DEL...
+	jne	2f
+	mov	$0x08, %eax	# look like BS
+2:
+	pop	%edx
+	pop	%ebp
+	ret
+
+/*
+ * int serial_ischar(void)
+ *       if there is a character pending, return true; otherwise return 0
+ */
+ENTRY(serial_ischar)
+	push	%ebp
+	mov	%esp, %ebp
+	push	%edx
+
+	xorl	%eax, %eax
+	mov	$COMCONSOLE + 5, %edx	# line status reg
+	inb	%dx, %al
+	andb	$0x01, %al		# RX char available?
+
+	pop	%edx
+	pop	%ebp
+	ret
+
+/*
+ * void init_serial(void)
+ * 	initialize the serial console port to 9600 Bd, 8 bpc
+ */
+ENTRY(init_serial)
+	push	%ebp
+	mov	%esp, %ebp
+	push	%edx
+
+	mov	$COMCONSOLE + 3, %edx	# line control reg
+	movb	$0x80, %al
+	outb	%al, %dx	# enable DLAB
+
+	sub	$3, %edx	# divisor latch, low byte
+	mov	$12, %ax	# divisor 12: 9600 Bd
+	outb	%al, %dx
+	inc	%edx		# divisor latch, high byte
+	movb	%ah, %al
+	outb	%al, %dx
+
+	add	$2, %edx	# line control reg
+	movb	$0x13, %al
+	outb	%al, %dx	# 8 bit, no parity, 1 stop bit
+
+	inc	%edx		# modem control reg
+	mov	$3, %al
+	outb	%al, %dx	# enable DTR/RTS
+
+	/* now finally, flush the input buffer */
+	inc	%edx		# line status reg
+1:
+	inb	%dx, %al
+	testb	$0x01, %al
+	jz	2f		# no more characters buffered
+	sub	$5, %edx	# rx buffer reg
+	inb	%dx, %al	# throw away
+	add	$5, %edx
+	jmp	1b
+2:
+	pop	%edx
+	pop	%ebp
+	ret