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use bios;
def sector_size: u32 = 512;
export type error = !void;
// Converts lba to the CHS format
fn lbatochs(lba: u32) (u16, u16, u16) = {
const temp = lba / bios::drive_sectors_per_track;
const sector = (lba % bios::drive_sectors_per_track) + 1;
const head = temp % bios::drive_heads;
const cylinder = temp / bios::drive_heads;
return (cylinder: u16, head: u16, sector: u16);
};
// Reads the sector at lba and place it into the workspace buffer
fn bios_read(lba: u32) (void | error) = {
const chs = lbatochs(lba);
const readcount = len(bios::ws): u32 / sector_size;
// AH=0x2 (read disk) AL=1 (read 1 sector)
bios::regs.eax = 0x2 << 8 | readcount;
// CH=cylinder CL=sector
bios::regs.ecx = chs.0 << 8 | chs.2;
// DH=head DL=driveno
bios::regs.edx = chs.1 << 8 | bios::drive_number;
let ws = (&bios::ws): uintptr;
bios::regs.es = (ws / 16): u16;
bios::regs.ebx = (ws % 16): u32;
bios::call(0x13);
if (bios::regs.eax != readcount) {
return error;
};
};
export fn read(addr: u32, count: size, dest: *[*]u8) (void | error) = {
// the amount of sectors fitting in the workspace (cannot be make a global constant yet, an assertion fails)
const readcount = len(bios::ws): u32 / sector_size;
// the starting lba
let lba = addr / sector_size;
// the reading head (for starting to read bytes not aligned with the sector)
let head = addr % len(bios::ws);
let cursor = 0z;
for (true) {
bios_read(lba)?;
for (head < len(bios::ws)) {
// XXX: use memmove
dest[cursor] = bios::ws[head];
head += 1;
cursor += 1;
if (cursor >= count) {
return;
};
};
head = 0;
lba += readcount;
};
};
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