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3fdb1c14f1
If your main module has this declaration:
STATIC_YOINK("vga_console");
Then a VGA driver will be linked into your executable which
displays your stdio characters on the PC display, whereas
before we could only use the serial port. Your display is an
ANSI terminal and it's still a work in progress.
66 lines
3.7 KiB
ArmAsm
66 lines
3.7 KiB
ArmAsm
/*-*- mode:unix-assembly; indent-tabs-mode:t; tab-width:8; coding:utf-8 -*-│
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│vi: set et ft=asm ts=8 tw=8 fenc=utf-8 :vi│
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ This is free and unencumbered software released into the public domain. │
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│ │
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│ Anyone is free to copy, modify, publish, use, compile, sell, or │
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│ distribute this software, either in source code form or as a compiled │
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│ binary, for any purpose, commercial or non-commercial, and by any │
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│ means. │
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│ │
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│ In jurisdictions that recognize copyright laws, the author or authors │
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│ of this software dedicate any and all copyright interest in the │
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│ software to the public domain. We make this dedication for the benefit │
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│ of the public at large and to the detriment of our heirs and │
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│ successors. We intend this dedication to be an overt act of │
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│ relinquishment in perpetuity of all present and future rights to this │
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│ software under copyright law. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, │
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│ EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF │
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│ MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. │
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│ IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR │
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│ OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, │
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│ ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR │
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│ OTHER DEALINGS IN THE SOFTWARE. │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/macros.internal.h"
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// Code snippet for initializing the VGA video mode for bare metal.
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//
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// If a program requests VGA support (by yoinking vga_console),
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// and it is started in bare metal mode, then try to ensure that
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// the VGA monitor is in a known mode. This is easier to do while
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// the program is still running in real mode.
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//
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// This module also ropes in the sys_writev_vga routine, which
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// implements the actual VGA console output under x86-64 long mode.
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//
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// @see rlinit & .sort.text.real.init.* (ape/ape.S)
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// @see ape/ape.lds
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// @see sys_writev_vga (libc/vga/writev-vga.c)
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.section .sort.text.real.init.2,"ax",@progbits
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.code16
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mov $0x4f03,%ax # get current video mode via VESA
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int $0x10
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cmp $0x004f,%ax # is VESA a thing here?
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jz 1f
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mov $0x0f,%ah # if not, get the video mode via a
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int $0x10 # classical BIOS call
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cbtw
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xchgw %ax,%bx
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1: mov $0x0003,%ax # check if we are in a 80 × ? × 16
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cmp %ax,%bx # text mode
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jnz 2f
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cmpb $25-1,0x0484 # check if number of screen rows
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jnz 2f # (BDA.ROWS + 1) is 25; if so, then
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mov $0x0500,%ax # just make sure we are on display
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# page 0
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2: int $0x10 # otherwise, change the video mode
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.previous
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.code64
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.section .rodata,"a",@progbits
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vga_console:
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.endobj vga_console,globl,hidden
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.previous
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.yoink sys_writev_vga
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