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/// BIOS starts with video mode 0h.
/// * 80x25 text mode
/// * 16 colors (4bit)
/// http://www.ctyme.com/intr/rb-0069.htm
pub const COLS = 80;
pub const ROWS = 25;
/// BIOS CALL - video teletype output.
/// http://www.ctyme.com/intr/rb-0106.htm
pub fn putc(c: u8) void {
// ah=0eh (call nr)
// al=c (ascii char to write)
const ax = (@as(u16, 0xe) << 8) | c;
_ = asm volatile (
\\int $0x10
: // No outputs.
: [a] "{ax}" (ax), // BIOS call number + char to write.
: "cc"
);
// On linefeed also write a carriage return to move to column 0.
if (c == '\n') {
putc('\r');
}
}
const E820 = extern struct {
base: u64 = 0,
size: u64 = 0,
kind: u32 = 0,
attr: u32 = 1, // ACPI 3.0 compat
};
/// BIOS CALL - get system memory map
/// http://www.ctyme.com/intr/rb-1741.htm
/// https://wiki.osdev.org/Detecting_Memory_(x86)#BIOS_Function:_INT_0x15,_EAX_=_0xE820
pub fn e820(next_ebx: u32) ?struct { e820: E820, ebx: u32 } {
var res = E820{};
// Setup call number.
var eax: u32 = 0xe820;
// Setup size of entry, bios call will return actual bytes written.
var ecx: u32 = @sizeOf(@TypeOf(res));
// Setup continuation code, next one will be returned from the bios call.
var ebx: u32 = next_ebx;
const carry = asm volatile (
\\int $0x15
\\setc %[c]
: // Outputs.
[n] "+{eax}" (eax),
[l] "+{ecx}" (ecx),
[o] "+{ebx}" (ebx),
[c] "={dl}" (-> u8), // Returns carry bit, recycle dl from dx.
: // Inputs.
[p] "{edi}" (&res), // Pointer to E820 entry.
[m] "{edx}" (0x534D4150), // Magic number (b"SMAP").
: // Clobbers.
"cc"
);
// Call failed if carry is set.
if (carry == 1) {
return null;
}
// Call failed if magic number is not returned in eax.
if (eax != 0x534D4150) {
return null;
}
// Call failed if partial entry is written.
if (ecx < 20) {
return null;
}
return .{ .e820 = res, .ebx = ebx };
}
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