diff --git a/sys/boot/i386/btx/btx/Makefile b/sys/boot/i386/btx/btx/Makefile
index d3ead1b889fe..1d03cfdf5bd8 100644
--- a/sys/boot/i386/btx/btx/Makefile
+++ b/sys/boot/i386/btx/btx/Makefile
@@ -14,6 +14,15 @@ BOOT_BTX_FLAGS=0x0
 
 AFLAGS+=	--defsym BTX_FLAGS=${BOOT_BTX_FLAGS}
 
+.if defined(BTX_SERIAL)
+BOOT_COMCONSOLE_PORT?= 0x3f8
+BOOT_COMCONSOLE_SPEED?= 9600
+B2SIOFMT?=	0x3
+
+M4FLAGS+=	-DBTX_SERIAL -DSIOPRT=${BOOT_COMCONSOLE_PORT} \
+		-DSIOFMT=${B2SIOFMT} -DSIOSPD=${BOOT_COMCONSOLE_SPEED}
+.endif
+
 ORG=	0x9000
 
 all: btx
diff --git a/sys/boot/i386/btx/btx/btx.S b/sys/boot/i386/btx/btx/btx.S
index b04299bce1ee..afa20fd51934 100644
--- a/sys/boot/i386/btx/btx/btx.S
+++ b/sys/boot/i386/btx/btx/btx.S
@@ -240,6 +240,9 @@ init.8: 	xorl %ecx,%ecx			# Zero
 		movb $0x7,%cl			# Set remaining
 init.9:		push $0x0			#  general
 		loop init.9			#  registers
+ifdef(`BTX_SERIAL',`
+		call sio_init			# setup the serial console
+')
 		popa				#  and initialize
 		popl %es			# Initialize
 		popl %ds			#  user
@@ -967,6 +970,80 @@ putstr: 	lodsb				# Load char
 		testb %al,%al			# End of string?
 		jnz putstr.0			# No
 		ret				# To caller
+ifdef(`BTX_SERIAL',`
+		.set SIO_PRT,SIOPRT		# Base port
+		.set SIO_FMT,SIOFMT		# 8N1
+		.set SIO_DIV,(115200/SIOSPD)	# 115200 / SPD
+
+# void sio_init(void)
+
+sio_init:	movw $SIO_PRT+0x3,%dx		# Data format reg
+		movb $SIO_FMT|0x80,%al		# Set format
+		outb %al,(%dx)			#  and DLAB
+		pushl %edx			# Save
+		subb $0x3,%dl			# Divisor latch reg
+		movw $SIO_DIV,%ax		# Set
+		outw %ax,(%dx)			#  BPS
+		popl %edx			# Restore
+		movb $SIO_FMT,%al		# Clear
+		outb %al,(%dx)			#  DLAB
+		incl %edx			# Modem control reg
+		movb $0x3,%al			# Set RTS,
+		outb %al,(%dx)			#  DTR
+		incl %edx			# Line status reg
+
+# void sio_flush(void)
+
+sio_flush.0:	call sio_getc.1 		# Get character
+sio_flush:	call sio_ischar 		# Check for character
+		jnz sio_flush.0 		# Till none
+		ret				# To caller
+
+# void sio_putc(int c)
+
+sio_putc:	movw $SIO_PRT+0x5,%dx		# Line status reg
+		xor %ecx,%ecx			# Timeout
+		movb $0x40,%ch			#  counter
+sio_putc.1:	inb (%dx),%al			# Transmitter
+		testb $0x20,%al 		#  buffer empty?
+		loopz sio_putc.1		# No
+		jz sio_putc.2			# If timeout
+		movb 0x4(%esp,1),%al		# Get character
+		subb $0x5,%dl			# Transmitter hold reg
+		outb %al,(%dx)			# Write character
+sio_putc.2:	ret $0x4			# To caller
+
+# int sio_getc(void)
+
+sio_getc:	call sio_ischar 		# Character available?
+		jz sio_getc			# No
+sio_getc.1:	subb $0x5,%dl			# Receiver buffer reg
+		inb (%dx),%al			# Read character
+		ret				# To caller
+
+# int sio_ischar(void)
+
+sio_ischar:	movw $SIO_PRT+0x5,%dx		# Line status register
+		xorl %eax,%eax			# Zero
+		inb (%dx),%al			# Received data
+		andb $0x1,%al			#  ready?
+		ret				# To caller
+
+#
+# Output character AL to the serial console.
+#
+putchr: 	pusha				# Save
+		cmpb $10, %al			# is it a newline?
+		jne putchr.1			#  no?, then leave
+		push $13			# output a carriage
+		call sio_putc			#  return first
+		movb $10, %al			# restore %al
+putchr.1:	pushl %eax			# Push the character
+						#  onto the stack
+		call sio_putc			# Output the character
+		popa				# Restore
+		ret				# To caller
+',`
 #
 # Output character AL to the console.
 #
diff --git a/sys/boot/i386/btx/btx/btx.s b/sys/boot/i386/btx/btx/btx.s
index b04299bce1ee..afa20fd51934 100644
--- a/sys/boot/i386/btx/btx/btx.s
+++ b/sys/boot/i386/btx/btx/btx.s
@@ -240,6 +240,9 @@ init.8: 	xorl %ecx,%ecx			# Zero
 		movb $0x7,%cl			# Set remaining
 init.9:		push $0x0			#  general
 		loop init.9			#  registers
+ifdef(`BTX_SERIAL',`
+		call sio_init			# setup the serial console
+')
 		popa				#  and initialize
 		popl %es			# Initialize
 		popl %ds			#  user
@@ -967,6 +970,80 @@ putstr: 	lodsb				# Load char
 		testb %al,%al			# End of string?
 		jnz putstr.0			# No
 		ret				# To caller
+ifdef(`BTX_SERIAL',`
+		.set SIO_PRT,SIOPRT		# Base port
+		.set SIO_FMT,SIOFMT		# 8N1
+		.set SIO_DIV,(115200/SIOSPD)	# 115200 / SPD
+
+# void sio_init(void)
+
+sio_init:	movw $SIO_PRT+0x3,%dx		# Data format reg
+		movb $SIO_FMT|0x80,%al		# Set format
+		outb %al,(%dx)			#  and DLAB
+		pushl %edx			# Save
+		subb $0x3,%dl			# Divisor latch reg
+		movw $SIO_DIV,%ax		# Set
+		outw %ax,(%dx)			#  BPS
+		popl %edx			# Restore
+		movb $SIO_FMT,%al		# Clear
+		outb %al,(%dx)			#  DLAB
+		incl %edx			# Modem control reg
+		movb $0x3,%al			# Set RTS,
+		outb %al,(%dx)			#  DTR
+		incl %edx			# Line status reg
+
+# void sio_flush(void)
+
+sio_flush.0:	call sio_getc.1 		# Get character
+sio_flush:	call sio_ischar 		# Check for character
+		jnz sio_flush.0 		# Till none
+		ret				# To caller
+
+# void sio_putc(int c)
+
+sio_putc:	movw $SIO_PRT+0x5,%dx		# Line status reg
+		xor %ecx,%ecx			# Timeout
+		movb $0x40,%ch			#  counter
+sio_putc.1:	inb (%dx),%al			# Transmitter
+		testb $0x20,%al 		#  buffer empty?
+		loopz sio_putc.1		# No
+		jz sio_putc.2			# If timeout
+		movb 0x4(%esp,1),%al		# Get character
+		subb $0x5,%dl			# Transmitter hold reg
+		outb %al,(%dx)			# Write character
+sio_putc.2:	ret $0x4			# To caller
+
+# int sio_getc(void)
+
+sio_getc:	call sio_ischar 		# Character available?
+		jz sio_getc			# No
+sio_getc.1:	subb $0x5,%dl			# Receiver buffer reg
+		inb (%dx),%al			# Read character
+		ret				# To caller
+
+# int sio_ischar(void)
+
+sio_ischar:	movw $SIO_PRT+0x5,%dx		# Line status register
+		xorl %eax,%eax			# Zero
+		inb (%dx),%al			# Received data
+		andb $0x1,%al			#  ready?
+		ret				# To caller
+
+#
+# Output character AL to the serial console.
+#
+putchr: 	pusha				# Save
+		cmpb $10, %al			# is it a newline?
+		jne putchr.1			#  no?, then leave
+		push $13			# output a carriage
+		call sio_putc			#  return first
+		movb $10, %al			# restore %al
+putchr.1:	pushl %eax			# Push the character
+						#  onto the stack
+		call sio_putc			# Output the character
+		popa				# Restore
+		ret				# To caller
+',`
 #
 # Output character AL to the console.
 #