1 files changed, 70 insertions, 4 deletions
diff --git a/bios/drive/drive.ha b/bios/drive/drive.ha
index 35cccca..a2992b8 100644
--- a/bios/drive/drive.ha
+++ b/bios/drive/drive.ha
@@ -1,5 +1,71 @@
-export let @symbol("drive_no") drive_no: u8;
-export let @symbol("drive_spt") drive_spt: u8;
-export let @symbol("drive_heads") drive_heads: u8;
+use bios;
 
-export fn read() void;
+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;
+	};
+	
+};