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Bare metal VGA: ensure correct initial video mode, & obtain

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initial cursor position as left by BIOS
This commit is contained in:
tkchia 2022-09-04 17:12:03 +00:00
parent 57faaa9c5a
commit aeacc4239d
2 changed files with 77 additions and 5 deletions
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66
libc/vga/vga-init.S Normal file
View file

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

16
libc/vga/writev-vga.c
View file

@ -41,9 +41,7 @@ typedef struct {
typedef char_cell_t char_row_t[WIDTH];
const char vga_console[0];
static unsigned short height = 25, curr_row = 12, curr_col = 0;
static unsigned short height = 25, curr_row, curr_col;
static uint8_t curr_attr = 0x07;
static void scroll(void) {
@ -71,8 +69,6 @@ static void updatexy_vga(void) {
}
static void writec_vga(char c) {
/* TODO: ensure screen in a known mode (text or graphics), at rlinit time */
/* TODO: use our own font, rather than rely on BIOS's CP437 font */
/* TODO: handle UTF-8 multi-bytes */
/* TODO: handle VT102 escape sequences */
/* TODO: maybe make BEL (\a) character code emit an alarm of some sort */
@ -127,3 +123,13 @@ ssize_t sys_writev_vga(struct Fd *fd, const struct iovec *iov, int iovlen) {
updatexy_vga();
return wrote;
}
__attribute__((__constructor__)) static textstartup void _vga_init(void) {
/* Get the initial cursor position from the BIOS data area. */
typedef struct {
unsigned char col, row;
} bios_curs_pos_t;
bios_curs_pos_t pos = *(bios_curs_pos_t *)(BANE + 0x0450ull);
curr_row = pos.row;
curr_col = pos.col;
}