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+#
+# Copyright (c) 1999 Global Technology Associates, Inc.
+# All rights reserved.
+#
+# 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.
+# 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.
+#
+# THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
+#
+# From: btx.s 1.10 1999/02/25 16:27:41 rnordier
+# $FreeBSD$
+#
+
+# Screen defaults and assumptions.
+
+ .set SCR_MAT,0x7 # Mode/attribute
+ .set SCR_COL,0x50 # Columns per row
+ .set SCR_ROW,0x19 # Rows per screen
+
+# BIOS Data Area locations.
+
+ .set BDA_SCR,0x449 # Video mode
+ .set BDA_POS,0x450 # Cursor position
+
+ .globl crt_putchr
+
+# void crt_putchr(int c)
+
+crt_putchr: movb 0x4(%esp,1),%al # Get character
+ pusha # Save
+ xorl %ecx,%ecx # Zero for loops
+ movb $SCR_MAT,%ah # Mode/attribute
+ movl $BDA_POS,%ebx # BDA pointer
+ movw (%ebx),%dx # Cursor position
+ movl $0xb8000,%edi # Regen buffer (color)
+ cmpb %ah,BDA_SCR-BDA_POS(%ebx) # Mono mode?
+ jne crt_putchr.1 # No
+ xorw %di,%di # Regen buffer (mono)
+crt_putchr.1: cmpb $0xa,%al # New line?
+ je crt_putchr.2 # Yes
+ xchgl %eax,%ecx # Save char
+ movb $SCR_COL,%al # Columns per row
+ mulb %dh # * row position
+ addb %dl,%al # + column
+ adcb $0x0,%ah # position
+ shll %eax # * 2
+ xchgl %eax,%ecx # Swap char, offset
+ movw %ax,(%edi,%ecx,1) # Write attr:char
+ incl %edx # Bump cursor
+ cmpb $SCR_COL,%dl # Beyond row?
+ jb crt_putchr.3 # No
+crt_putchr.2: xorb %dl,%dl # Zero column
+ incb %dh # Bump row
+crt_putchr.3: cmpb $SCR_ROW,%dh # Beyond screen?
+ jb crt_putchr.4 # No
+ leal 2*SCR_COL(%edi),%esi # New top line
+ movw $(SCR_ROW-1)*SCR_COL/2,%cx # Words to move
+ rep # Scroll
+ movsl # screen
+ movb $' ',%al # Space
+ movb $SCR_COL,%cl # Columns to clear
+ rep # Clear
+ stosw # line
+ movb $SCR_ROW-1,%dh # Bottom line
+crt_putchr.4: movw %dx,(%ebx) # Update position
+ popa # Restore
+ ret # To caller