reading from disk

.asm-lsp.toml

@@ -0,0 +1,21 @@
+[default_config]
+version = "0.10.0"
+assembler = "nasm"
+instruction_set = "x86/x86-64"
+
+[default_config.opts]
+compiler = "zig"
+compile_flags_txt = [
+  "cc",
+  "-x",
+  "assembler-with-cpp",
+  "-g",
+  "-Wall",
+  "-Wextra",
+  "-pedantic",
+  "-pedantic-errors",
+  "-std=c2y",
+  "-mllvm --x86-asm-syntax=intel",
+]
+diagnostics = true
+default_diagnostics = false

.gitignore

@@ -1,2 +1,3 @@
 zig-out
 .zig-cache
+.kate-swp

build.zig

@@ -7,17 +7,24 @@ pub fn build(b: *std.Build) void {
     const initramfs = addNasmFiles(b, AddNasmFilesOptions{
         .filename = "src/initramfs.asm",
         .outputname = "initramfs.bin",
-        .addAsObjFile = false,
+        .flags = &.{"-f bin"},
+    });
+    const kernel = addNasmFiles(b, AddNasmFilesOptions{
+        .filename = "src/kernel.asm",
+        .outputname = "kernel.bin",
         .flags = &.{"-f bin"},
     });
 
-    const initramfs_install = b.addInstallBinFile(initramfs.obj, "initramfs.img");
+    var floppy = createFloppy(b, "main_floppy.img");
-    initramfs_install.step.dependOn(&truncate(b, initramfs).step);
+    floppy.run = formatFloppyFat12(b, floppy);
 
-    b.getInstallStep().dependOn(&initramfs_install.step);
+    const img_install = b.addInstallBinFile(floppy.obj, "main_floppy.img");
+    img_install.step.dependOn(&installImgToFloppy(b, floppy, initramfs, kernel).step);
+
+    b.getInstallStep().dependOn(&img_install.step);
 
     const run = b.addSystemCommand(&.{ "qemu-system-i386", "-fda" });
-    run.addFileArg(b.path("zig-out/bin/initramfs.img"));
+    run.addFileArg(floppy.obj);
 
     const run_step = b.step("run", "run the os in qemu");
     run_step.dependOn(&run.step);
@@ -26,7 +33,6 @@ pub fn build(b: *std.Build) void {
 const AddNasmFilesOptions = struct {
     filename: []const u8,
     outputname: ?[]const u8 = null,
-    addAsObjFile: bool = true,
     flags: []const []const u8 = &.{},
 };
 
@@ -35,6 +41,46 @@ const NasmFile = struct {
     obj: std.Build.LazyPath,
 };
 
+const Floppydisk = NasmFile;
+
+fn createFloppy(b: *std.Build, name: []const u8) Floppydisk {
+    const dd = b.addSystemCommand(&.{ "dd", "if=/dev/zero" });
+    const Floppy = dd.addPrefixedOutputFileArg("of=", name);
+    dd.addArgs(&.{ "bs=512", "count=2880" });
+
+    return Floppydisk{
+        .run = dd,
+        .obj = Floppy,
+    };
+}
+
+fn formatFloppyFat12(b: *std.Build, floppy: Floppydisk) *std.Build.Step.Run {
+    const mkfs = b.addSystemCommand(&.{ "mkfs.fat", "-F12", "-nNBOS" });
+    mkfs.addFileArg(floppy.obj);
+
+    mkfs.step.dependOn(&floppy.run.step);
+
+    return mkfs;
+}
+
+fn installImgToFloppy(b: *std.Build, floppy: Floppydisk, bootloader: NasmFile, kernel: NasmFile) *std.Build.Step.Run {
+    const dd = b.addSystemCommand(&.{"dd"});
+    dd.addPrefixedFileArg("if=", bootloader.obj);
+    dd.addPrefixedFileArg("of=", floppy.obj);
+    dd.addArg("conv=notrunc");
+    dd.step.dependOn(&floppy.run.step);
+    dd.step.dependOn(&bootloader.run.step);
+
+    const mcopy = b.addSystemCommand(&.{"mcopy"});
+    mcopy.addPrefixedFileArg("-i", floppy.obj);
+    mcopy.addFileArg(kernel.obj);
+    mcopy.addArg("::kernel.bin");
+    mcopy.step.dependOn(&dd.step);
+    mcopy.step.dependOn(&kernel.run.step);
+
+    return mcopy;
+}
+
 // adapted from https://codeberg.org/raddari/zig-nasm-lib.git
 fn addNasmFiles(b: *std.Build, options: AddNasmFilesOptions) NasmFile {
     std.debug.assert(!std.fs.path.isAbsolute(options.filename));
@@ -52,12 +98,3 @@ fn addNasmFiles(b: *std.Build, options: AddNasmFilesOptions) NasmFile {
         .obj = obj,
     };
 }
-
-fn truncate(b: *std.Build, bin: NasmFile) *std.Build.Step.Run {
-    const exec = b.addSystemCommand(&.{"truncate"});
-    exec.addArgs(&.{ "-s", "1440k" });
-    exec.addFileArg(bin.obj);
-    exec.step.dependOn(&bin.run.step);
-
-    return exec;
-}

src/initramfs.asm

@@ -2,8 +2,40 @@
 org 0x7C00
 bits 16
 
+
 %define ENDL 0x0D, 0x0A
 
+;
+; FAT12 Header
+;
+jmp short start
+nop
+
+bdb_oem:					db "mkfs.fat"
+bdb_bytes_per_sector:		dw 512
+bdb_sectors_per_cluster:	db 1
+bdb_reserved_sectors:		dw 1
+bdb_fat_count:				db 2
+bdb_dir_entries_count:		dw 0E0h
+bdb_total_sectors:			dw 2880
+bdb_media_descriptor_type:	db 0F0h
+bdb_sectors_per_fat:		dw 9
+bdb_sectors_per_track:		dw 18
+bdb_heads:					dw 2
+bdb_hidden_sectors:			dd 0
+bdb_large_sector_count:		dd 0
+
+; Extended boot record
+ebr_drive_number:			db 0
+							db 0
+ebr_signature:				db 29h
+ebr_volume_id:				db 68h, 6Fh, 6Dh, 6Fh
+ebr_volume_laber:			db 'zos disk   '
+ebr_system_id:				db 'FAT12   '
+
+
+
+
 start:
 	jmp main
 
@@ -47,16 +79,139 @@ main:
 	mov ss, ax
 	mov sp, 0x7C00	; stack grows downward from where we are loaded in memory
 
-	; print the hello world
+	mov si, msg_startup
-	mov si, msg_hello
 	call echo
 
+	mov si, msg_reading_from_disk
+	call echo
+	mov [ebr_drive_number], dl
+
+	mov ax, 1								; second sector from disk
+	mov cl, 1								; 1 sector to read
+	mov bx, 0x7E00							; data should be after the bootloader
+	call disk_read
+
+	cli
+	hlt
+
+; errors
+
+floppy_error:
+	mov si, msg_read_failed
+	call echo
+	jmp .wait_and_reboot
+
+.wait_and_reboot:
+	mov ah, 0
+	int 16h
+	
+	jmp 0FFFFh:0							; jump to start of bios, should reboot
+
 	hlt
 
 .halt:
+	cli										; disable interrupts, this way we shouldn't be able to get out of halt
+	hlt
 	jmp .halt
 
-msg_hello: db 'Hello, world!', ENDL, 0
+
+;
+; args: 
+;	ax = lba adress
+; return:
+; 	cx[0..5] = sector number
+; 	cx[6-15] = cilinder number
+; 	dh: head
+;
+lba_to_chs:
+	push ax
+	push dx
+
+	xor dx, dx								; clear dw
+	div word [bdb_sectors_per_track]		; ax = LBA / SectorsPerTrack
+											; dx = LBA % SectorsPerTrack
+
+	inc dx
+	mov cx, dx								; cx = sector
+
+	xor dx, dx								; clear dx
+	div word [bdb_heads]					; ax = (LBA / SectorsPerTrack) / Heads = cylinder
+	                                        ; dx = (LBA / SectorsPerTrack) % Heads = head
+	mov dh, dl
+	mov ch, al
+	shl ah, 6
+	or cl, ah								; put upper 2 bits of cylinder in CL
+
+	pop ax
+	mov dl, al
+	pop ax
+
+	ret
+
+
+;
+; args:
+;	ax = LBA adress
+;	cl = number of sectors to read
+;	dl = drive number
+;	es:bx = pointer to where to store the data
+;
+
+disk_read:
+	push ax
+	push bx
+	push cx
+	push dx
+	push di
+
+	push cx									; cx will be overridden
+	call lba_to_chs
+	pop ax									; al = number of sectors to read
+	mov ah, 02h
+	mov di, 3								; hoe many times to try
+
+.retry:
+	pusha
+	stc										; set carry flag
+	int 13h									; if no carry flag => it work
+
+	jnc .done
+
+	; read fail
+	popa
+	call disk_reset
+	dec di
+
+	test di, di
+	jnz .retry
+
+.fail:
+	jmp floppy_error
+
+.done:
+	popa
+	
+	pop di
+	pop dx
+	pop cx
+	pop bx
+	pop ax
+	ret
+
+; arg: dl = drive number
+
+disk_reset:
+	pusha
+	mov ah, 0
+	stc										; set carry
+	int 13h	
+	jc floppy_error
+	popa
+	ret
+
+msg_startup: 								db 'starting zos, please hold while we check for any problems', ENDL, 0
+msg_reading_from_disk:						db 'testing reading from disk', ENDL, 0
+msg_read_failed:							db 'error when trying to read from floppy', ENDL, 0
 
 times 510-($-$$) db 0
 dw 0AA55h

src/kernel.asm

@@ -0,0 +1,62 @@
+; vim: ft=nasm
+org 0x7C00
+bits 16
+
+%define ENDL 0x0D, 0x0A
+
+start:
+	jmp main
+
+; 
+; echo:
+; print something to the screen
+;  - ds:si points to string
+;
+echo:
+	; save the registers we want to modify
+	push si
+	push ax
+	push bx
+
+	mov ah, 0xe
+	mov bh, 0
+
+.loop:
+	lodsb			; load byte from ds:si to al
+	or al, al		; check if next char is null
+	jz .done
+
+	int 0x10
+	jmp .loop
+
+.done:
+	pop bx
+	pop ax
+	pop si
+	ret
+
+main:
+
+	; setup data segments
+	; use ax as and intermediary as we can't write to es/ds directly
+	mov ax, 0
+	mov ds, ax
+	mov es, ax
+
+	; setup stack
+	mov ss, ax
+	mov sp, 0x7C00	; stack grows downward from where we are loaded in memory
+
+	; print the hello world
+	mov si, msg_hello
+	call echo
+
+	hlt
+
+.halt:
+	jmp .halt
+
+msg_hello: db 'Hello, world!', ENDL, 0
+
+times 510-($-$$) db 0
+dw 0AA55h