From dfd5ca4a0f34f9346ff2decbd3cfc8e3f6fccc04 Mon Sep 17 00:00:00 2001
From: Jeremy Soller <jackpot51@gmail.com>
Date: Tue, 6 Sep 2022 15:51:30 -0600
Subject: [PATCH] Use CHS to support CD boot
---
asm/x86-unknown-none/stage1.asm | 90 ++++++++++++++++++++++++++++++---
src/os/bios/disk.rs | 85 +++++++++++++++++++++++++------
2 files changed, 153 insertions(+), 22 deletions(-)
diff --git a/asm/x86-unknown-none/stage1.asm b/asm/x86-unknown-none/stage1.asm
index 26740c9..d2175e1 100644
--- a/asm/x86-unknown-none/stage1.asm
+++ b/asm/x86-unknown-none/stage1.asm
@@ -22,18 +22,42 @@ stage1: ; dl comes with disk
; save disk number
mov [disk], dl
- mov si, name
+ mov si, stage_msg
call print
+ mov al, '1'
+ call print_char
call print_line
+ ; read CHS gemotry
+ ; CL (bits 0-5) = maximum sector number
+ ; CL (bits 6-7) = high bits of max cylinder number
+ ; CH = low bits of maximum cylinder number
+ ; DH = maximum head number
+ mov ah, 0x08
+ mov dl, [disk]
+ xor di, di
+ int 0x13
+ jc error ; carry flag set on error
+ mov bl, ch
+ mov bh, cl
+ shr bh, 6
+ mov [chs.c], bx
+ shr dx, 8
+ inc dx ; returns heads - 1
+ mov [chs.h], dx
+ and cl, 0x3f
+ mov [chs.s], cl
+
mov eax, (stage2 - stage1) / 512
mov bx, stage2
mov cx, (stage3.end - stage2) / 512
mov dx, 0
call load
- mov si, finished
+ mov si, stage_msg
call print
+ mov al, '2'
+ call print_char
call print_line
jmp stage2.entry
@@ -70,11 +94,56 @@ load:
call print_dapack
+ cmp byte [chs.s], 0
+ jne .chs
+ ;INT 0x13 extended read does not work on CDROM!
mov dl, [disk]
mov si, DAPACK
mov ah, 0x42
int 0x13
- jc error
+ jc error ; carry flag set on error
+ ret
+
+.chs:
+ ; calculate CHS
+ xor edx, edx
+ mov eax, [DAPACK.addr]
+ div dword [chs.s] ; divide by sectors
+ mov ecx, edx ; move sector remainder to ecx
+ xor edx, edx
+ div dword [chs.h] ; divide by heads
+ ; eax has cylinders, edx has heads, ecx has sectors
+
+ ; Sector cannot be greater than 63
+ inc ecx ; Sector is base 1
+ cmp ecx, 63
+ ja error_chs
+
+ ; Head cannot be greater than 255
+ cmp edx, 255
+ ja error_chs
+
+ ; Cylinder cannot be greater than 1023
+ cmp eax, 1023
+ ja error_chs
+
+ ; Move CHS values to parameters
+ mov ch, al
+ shl ah, 6
+ and cl, 0x3f
+ or cl, ah
+ shl dx, 8
+
+ ; read from disk using CHS
+ mov al, [DAPACK.count]
+ mov ah, 0x02 ; disk read (CHS)
+ mov bx, [DAPACK.buf]
+ mov dl, [disk]
+ push es ; save ES
+ mov es, [DAPACK.seg]
+ int 0x13
+ pop es ; restore EC
+ jc error ; carry flag set on error
ret
print_dapack:
@@ -106,6 +175,9 @@ print_dapack:
ret
+error_chs:
+ mov ah, 0
+
error:
call print_line
@@ -116,7 +188,7 @@ error:
mov al, ' '
call print_char
- mov si, errored
+ mov si, error_msg
call print
call print_line
.halt:
@@ -126,12 +198,16 @@ error:
%include "print.asm"
-name: db "Redox Loader - Stage One",0
-errored: db "Could not read disk",0
-finished: db "Redox Loader - Stage Two",0
+stage_msg: db "Stage ",0
+error_msg: db "ERROR",0
disk: db 0
+chs:
+.c: dd 0
+.h: dd 0
+.s: dd 0
+
DAPACK:
db 0x10
db 0
diff --git a/src/os/bios/disk.rs b/src/os/bios/disk.rs
index 4f864f8..c24f48a 100644
--- a/src/os/bios/disk.rs
+++ b/src/os/bios/disk.rs
@@ -42,11 +42,33 @@ impl DiskAddressPacket {
pub struct DiskBios {
boot_disk: u8,
thunk13: extern "C" fn(),
+ chs_opt: Option<(u32, u32, u32)>,
}
impl DiskBios {
pub fn new(boot_disk: u8, thunk13: extern "C" fn()) -> Self {
- Self { boot_disk, thunk13 }
+ let chs_opt = unsafe {
+ let mut data = ThunkData::new();
+ data.eax = 0x0800;
+ data.edx = boot_disk as u32;
+ data.edi = 0;
+
+ data.with(thunk13);
+
+ let c =
+ (data.ecx >> 8) & 0xFF |
+ ((data.ecx >> 6) & 0x3) << 8;
+ let h = ((data.edx >> 8) & 0xFF) + 1;
+ let s = data.ecx & 0x3F;
+
+ Some((c, h, s))
+ };
+
+ Self {
+ boot_disk,
+ thunk13,
+ chs_opt,
+ }
}
}
@@ -69,21 +91,54 @@ impl Disk for DiskBios {
block + i as u64 * MAX_BLOCKS,
chunk.len() as u64 / BLOCK_SIZE
);
- ptr::write(DISK_ADDRESS_PACKET_ADDR as *mut DiskAddressPacket, dap);
-
- let mut data = ThunkData::new();
- data.eax = 0x4200;
- data.edx = self.boot_disk as u32;
- data.esi = DISK_ADDRESS_PACKET_ADDR as u32;
- data.with(self.thunk13);
-
- //TODO: return result on error
- let ah = ({ data.eax } >> 8) & 0xFF;
- assert_eq!(ah, 0);
-
- //TODO: check blocks transferred
- dap = ptr::read(DISK_ADDRESS_PACKET_ADDR as *mut DiskAddressPacket);
+ if let Some((c_max, h_max, s_max)) = self.chs_opt {
+ let s = (dap.address % s_max as u64) + 1;
+ assert!(s <= 63);
+
+ let tmp = dap.address / s_max as u64;
+ let h = tmp % h_max as u64;
+ assert!(h <= 255);
+
+ let c = tmp / h_max as u64;
+ assert!(c <= 1023);
+
+ let mut data = ThunkData::new();
+ data.eax =
+ 0x0200 |
+ (dap.sectors as u32);
+ data.ebx = dap.buffer as u32;
+ data.ecx =
+ (s as u32) |
+ (((c as u32) & 0xFF) << 8) |
+ ((((c as u32) >> 8) & 0x3) << 6);
+ data.edx =
+ (self.boot_disk as u32) |
+ ((h as u32) << 8);
+ data.es = dap.segment;
+
+ data.with(self.thunk13);
+
+ //TODO: return result on error
+ let ah = ({ data.eax } >> 8) & 0xFF;
+ assert_eq!(ah, 0);
+ } else {
+ ptr::write(DISK_ADDRESS_PACKET_ADDR as *mut DiskAddressPacket, dap);
+
+ let mut data = ThunkData::new();
+ data.eax = 0x4200;
+ data.edx = self.boot_disk as u32;
+ data.esi = DISK_ADDRESS_PACKET_ADDR as u32;
+
+ data.with(self.thunk13);
+
+ //TODO: return result on error
+ let ah = ({ data.eax } >> 8) & 0xFF;
+ assert_eq!(ah, 0);
+
+ //TODO: check blocks transferred
+ dap = ptr::read(DISK_ADDRESS_PACKET_ADDR as *mut DiskAddressPacket);
+ }
ptr::copy(DISK_BIOS_ADDR as *const u8, chunk.as_mut_ptr(), chunk.len());
}
--
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