From f2654038cbdfe5089522d27dff5ba063068599ea Mon Sep 17 00:00:00 2001
From: CrazyEttin <>
Date: Thu, 10 Jun 2021 18:16:14 +0300
Subject: [PATCH] Make the system compatible with Intel 8086 CPU, change the
 remaining media-dependent constants in the bootloader to variables, change
 the default media to a 360 KiB 5.25" floppy disk and offer 1.44 MB 3.5" disk
 as an option instead, and change labels used for data to variables because
 apparently using labels for data is not wise.

---
 SOURCE/BOOT.ASM     | 146 +++++++++++++++++++++++++++++---------------
 SOURCE/BYTE2HEX.INC |  23 +++++--
 SOURCE/CMPSTR.INC   |   8 ++-
 SOURCE/HELLO.INC    |   3 +-
 SOURCE/HELP.INC     |   3 +-
 SOURCE/KEYCODE.INC  |  17 ++----
 SOURCE/PRINTNL.INC  |   7 +--
 SOURCE/PRINTSTR.INC |   4 +-
 SOURCE/READCH.INC   |   1 -
 SOURCE/READSTR.INC  |  10 ++-
 SOURCE/SYSTEM.ASM   |  32 ++++------
 make.sh             |  11 +++-
 12 files changed, 161 insertions(+), 104 deletions(-)

diff --git a/SOURCE/BOOT.ASM b/SOURCE/BOOT.ASM
index f80d4fe..d856c6c 100644
--- a/SOURCE/BOOT.ASM
+++ b/SOURCE/BOOT.ASM
@@ -1,26 +1,54 @@
-[ORG 0x7c00]
+CPU 8086
+ORG 0x7c00
+
 jmp start
 nop
 
-;1.44 MB 3.5" floppy disk description table
-OEMLabel          db "ETTINOS "
-BytesPerSector    dw 0x200
-SectorsPerCluster db 0x1
-BootRecordSectors dw 0x1
-FATs              db 0x2
-RootEntries       dw 0xe0
-LogicalSectors    dw 0xb40
-MediaDescriptor   db 0xf0
-SectorsPerFAT     dw 0x9
-SectorsPerTrack   dw 0x12
-Sides             dw 0x2
-HiddenSectors     dd 0x0
-LargeSectors      dd 0x0
-DriveNumber       dw 0x0
-DriveSignature    db 0x29
-VolumeID          dd 0x0
-VolumeLabel       db "ETTINOS    "
-FileSystem        db "FAT12   "
+;Disk description tables
+
+%ifdef F1440
+;1.44 MB 3.5" floppy disk (enable by passing -d F1440 to NASM)
+oemlabel        db "ETTINOS "
+sectorsize      dw 0x200 ;bytes
+clustersize     db 0x1 ;sectors
+bootsectors     dw 0x1
+fats            db 0x2
+rootentries     dw 0xe0
+logicalsectors  dw 0xb40
+mediadescriptor db 0xf0
+sectorsperfat   dw 0x9
+sectorspertrack dw 0x12
+sides           dw 0x2
+hiddensectors   dd 0x0
+largesectors    dd 0x0
+driveid         dw 0x0
+drivesignature  db 0x29
+volumeid        dd 0x0
+volumelabel     db "ETTINOS    "
+filesystem      db "FAT12   "
+
+%else
+;360 KiB 5.25" floppy disk (default)
+oemlabel        db "ETTINOS "
+sectorsize      dw 0x200 ;bytes
+clustersize     db 0x2 ;sectors
+bootsectors     dw 0x1
+fats            db 0x2
+rootentries     dw 0x70
+logicalsectors  dw 0x2d0
+mediadescriptor db 0xfd
+sectorsperfat   dw 0x2
+sectorspertrack dw 0x9
+sides           dw 0x2
+hiddensectors   dd 0x0
+largesectors    dd 0x0
+driveid         dw 0x0
+drivesignature  db 0x29
+volumeid        dd 0x0
+volumelabel     db "ETTINOS    "
+filesystem      db "FAT12   "
+
+%endif
 
 start:
 
@@ -38,9 +66,13 @@ sti
 ;Store the boot device number
 mov [bootdev], dl
 
-;Load the root FAT
+;Load the root
 ;Set the source
-mov ax, 0x13
+mov ah, 0x0
+mov al, [fats]
+mul word [sectorsperfat]
+add ax, [bootsectors]
+push ax
 call calcsource
 ;Set the destination
 mov si, 0x7e00
@@ -48,18 +80,25 @@ mov bx, ds
 mov es, bx
 mov bx, si
 ;Set the size
-mov al, 0xe
+push dx
+mov ax, [rootentries]
+mov dx, 0x20
+mul dx
+mov dx, 0x0
+div word [sectorsize]
+pop dx
+push ax
 ;Load
 mov ah, 0x2
 int 0x13
 
-;Search the root FAT for the system FAT
+;Search the root for the system
 ;Set DI to the root FAT
 mov ax, ds
 mov es, ax
 mov di, 0x7e00
 ;Initialise the search loop
-mov cx, word [RootEntries]
+mov cx, word [rootentries]
 mov ax, 0x0
 search:
 ;Store CX in the stack
@@ -68,7 +107,7 @@ push cx
 mov si, sysfile
 mov cx, 0xb
 rep cmpsb
-je loadsysfat
+je loadfat
 ;Set DI to the next entry
 add ax, 0x20
 mov di, 0x7e00
@@ -78,7 +117,9 @@ pop cx
 loop search
 
 ;Load the system FAT
-loadsysfat:
+loadfat:
+;Load CX from the stack
+pop cx
 ;Store the first cluster
 mov ax, word [es:di+0xf]
 mov word [cluster], ax
@@ -89,16 +130,23 @@ call calcsource
 mov di, 0x7e00
 mov bx, di
 ;Set the size
-mov al, 0x9
+mov ax, [sectorsperfat]
 ;Load
 mov ah, 0x2
 int 0x13
 
-;Load the system
-loadsys:
+;Load the system file
+
+;Load a cluster
+loadcluster:
 ;Set the source
-mov ax, word [cluster]
-add ax, 0x1f
+pop bx
+pop ax
+push ax
+push bx
+add ax, bx
+sub ax, 0x2
+add ax, word [cluster]
 call calcsource
 ;Set the destination
 mov ax, 0x0
@@ -106,7 +154,7 @@ mov es, ax
 mov bx, word [pointer]
 ;Set the size
 mov al, 0x1
-;Load a cluster
+;Load
 mov ah, 0x2
 int 0x13
 
@@ -115,7 +163,7 @@ mov ax, [cluster]
 mov dx, 0x0
 mov bx, 0x3
 mul bx
-mov bx, 2
+mov bx, 0x2
 div bx
 mov si, 0x7e00
 add si, ax
@@ -123,45 +171,43 @@ mov ax, word [ds:si]
 or dx, dx
 jz even
 odd:
-shr ax, 4
-jmp contcluster
+shr ax, 1
+shr ax, 1
+shr ax, 1
+shr ax, 1
+jmp contcalc
 even:
 and ax, 0xfff
-contcluster:
+contcalc:
 mov word [cluster], ax
 cmp ax, 0xff8
 jge boot
 add word [pointer], 0x200
-jmp loadsys
+jmp loadcluster
 
 boot:
 jmp 0x0:0x9e00
 
-sysfile:
-db "SYSTEM  BIN"
+sysfile db "SYSTEM  BIN"
 
-bootdev:
-db 0
+bootdev db 0x0
 
-cluster:
-dw 0x0
-
-pointer:
-dw 0x9e00
+cluster dw 0x0
+pointer dw 0x9e00
 
 calcsource:
 push ax
 push bx
 mov bx, ax
 mov dx, 0x0
-div word [SectorsPerTrack]
+div word [sectorspertrack]
 add dl, 0x1
 mov cl, dl
 mov ax, bx
 mov dx, 0x0
-div word [SectorsPerTrack]
+div word [sectorspertrack]
 mov dx, 0x0
-div word [Sides]
+div word [sides]
 mov dh, dl
 mov ch, al
 pop bx
diff --git a/SOURCE/BYTE2HEX.INC b/SOURCE/BYTE2HEX.INC
index 655d346..78a6ac1 100644
--- a/SOURCE/BYTE2HEX.INC
+++ b/SOURCE/BYTE2HEX.INC
@@ -1,9 +1,15 @@
-;Converts a byte in AH to a hex string at DI.
+;Converts a byte in AL to a hex string at DI.
 
 byte2hex:
 
 ;Store the initial registers in the stack
-pusha
+push si
+push ax
+push bx
+push cx
+
+;Move the byte to AH
+mov ah, al
 
 ;Set a key for the hex digits
 mov si, .key
@@ -14,7 +20,10 @@ mov cx, 0x2
 .loop:
 
 ;Read a nibble
-rol ax, 0x4
+rol ax, 0x1
+rol ax, 0x1
+rol ax, 0x1
+rol ax, 0x1
 mov bx, ax
 
 ;Convert the nibble to a hex digit
@@ -30,9 +39,11 @@ dec cx
 jnz .loop
 
 ;Load the initial registers from the stack
-popa
+pop cx
+pop bx
+pop ax
+pop si
 
 ret
 
-.key:
-db "0123456789abcdef"
+.key db "0123456789abcdef"
diff --git a/SOURCE/CMPSTR.INC b/SOURCE/CMPSTR.INC
index 0eef00d..014cdda 100644
--- a/SOURCE/CMPSTR.INC
+++ b/SOURCE/CMPSTR.INC
@@ -1,9 +1,10 @@
-;Compares strings from SI and SI and sets the carry flag if they are equal and clears it if not.
+;Compares strings from SI and DI until a null and either sets the carry flag if they are equal or clears it if not.
 
 cmpstr:
 
 ;Store the initial registers in the stack
-pusha
+push ax
+push bx
 
 .loop:
 
@@ -38,6 +39,7 @@ stc
 .done:
 
 ;Load the initial registers from the stack
-popa
+pop bx
+pop ax
 
 ret
diff --git a/SOURCE/HELLO.INC b/SOURCE/HELLO.INC
index 1dc1afc..b3f7133 100644
--- a/SOURCE/HELLO.INC
+++ b/SOURCE/HELLO.INC
@@ -7,5 +7,4 @@ call println
 
 ret
 
-.hello:
-db "Hello world!", 0x0
\ No newline at end of file
+.hello db "Hello world!", 0x0
\ No newline at end of file
diff --git a/SOURCE/HELP.INC b/SOURCE/HELP.INC
index 02311f1..a8abcb8 100644
--- a/SOURCE/HELP.INC
+++ b/SOURCE/HELP.INC
@@ -7,5 +7,4 @@ call println
 
 ret
 
-.help:
-db "Input:", 0xd, 0xa, "* Typing a character overwrites the cursor location.", 0xd, 0xa, "* The erase (=tab) key erases the cursor location.", 0xd, 0xa, "* The space and backspace keys move the cursor.", 0xd, 0xa, "Commands:", 0xd, 0xa, "* echo: echoes its input.", 0xd, 0xa, "* hello: a hello world program.", 0xd, 0xa, "* help: you are reading it.", 0xd, 0xa, "* keycode: echoes the BIOS code of a key.", 0x0
+.help db "Input:", 0xd, 0xa, "* Typing a character overwrites the cursor location.", 0xd, 0xa, "* The erase (=tab) key erases the cursor location.", 0xd, 0xa, "* The space and backspace keys move the cursor.", 0xd, 0xa, "Commands:", 0xd, 0xa, "* echo: echoes its input.", 0xd, 0xa, "* hello: a hello world program.", 0xd, 0xa, "* help: you are reading it.", 0xd, 0xa, "* keycode: echoes the BIOS code of a key.", 0x0
diff --git a/SOURCE/KEYCODE.INC b/SOURCE/KEYCODE.INC
index fdfb321..e056e7e 100644
--- a/SOURCE/KEYCODE.INC
+++ b/SOURCE/KEYCODE.INC
@@ -15,12 +15,12 @@ mov si, .prefix
 call printstr
 
 ;Convert the scancode to a hex string
-mov ah, [.scan]
+mov al, [.scan]
 mov di, .keycode
 call byte2hex
 
 ;Convert the ascii value to a hex string
-mov ah, [.ascii]
+mov al, [.ascii]
 mov di, .keycode
 add di, 0x2
 call byte2hex
@@ -31,14 +31,9 @@ call println
 
 ret
 
-.prefix:
-db "0x", 0x0
+.prefix db "0x", 0x0
 
-.scan:
-db 0x0
+.scan db 0x0
+.ascii db 0x0
 
-.ascii:
-db 0x0
-
-.keycode:
-times 0x5 db 0x0
+.keycode times 0x5 db 0x0
diff --git a/SOURCE/PRINTNL.INC b/SOURCE/PRINTNL.INC
index 9d603db..481073f 100644
--- a/SOURCE/PRINTNL.INC
+++ b/SOURCE/PRINTNL.INC
@@ -3,16 +3,15 @@
 printnl:
 
 ;Store the initial registers in the stack
-pusha
+push si
 
 ;Print the newline
 mov si, .nl
 call printstr
 
 ;Load the initial registers from the stack
-popa
+pop si
 
 ret
 
-.nl:
-db 0xd, 0xa, 0x0
+.nl db 0xd, 0xa, 0x0
diff --git a/SOURCE/PRINTSTR.INC b/SOURCE/PRINTSTR.INC
index 1ba6070..7f3af5c 100644
--- a/SOURCE/PRINTSTR.INC
+++ b/SOURCE/PRINTSTR.INC
@@ -3,7 +3,7 @@
 printstr:
 
 ;Store the initial registers in the stack
-pusha
+push ax
 
 .loop:
 
@@ -24,6 +24,6 @@ jmp .loop
 .done:
 
 ;Load the initial registers from the stack
-popa
+pop ax
 
 ret
diff --git a/SOURCE/READCH.INC b/SOURCE/READCH.INC
index 012e022..9b0680e 100644
--- a/SOURCE/READCH.INC
+++ b/SOURCE/READCH.INC
@@ -25,5 +25,4 @@ pop bx
 mov ah, bh
 pop bx
 
-.done:
 ret
diff --git a/SOURCE/READSTR.INC b/SOURCE/READSTR.INC
index 2c96c0f..16b7d42 100644
--- a/SOURCE/READSTR.INC
+++ b/SOURCE/READSTR.INC
@@ -3,7 +3,10 @@
 readstr:
 
 ;Store the initial registers in the stack
-pusha
+push ax
+push bx
+push cx
+push dx
 
 ;Store the input length in the stack
 mov ah, 0
@@ -116,7 +119,10 @@ jmp .findend
 .done:
 
 ;Load the initial registers from the stack
-popa
+pop dx
+pop cx
+pop bx
+pop ax
 
 ret
 
diff --git a/SOURCE/SYSTEM.ASM b/SOURCE/SYSTEM.ASM
index 7d4eaae..5ea6f85 100644
--- a/SOURCE/SYSTEM.ASM
+++ b/SOURCE/SYSTEM.ASM
@@ -1,4 +1,6 @@
-[ORG 0x9e00]
+CPU 8086
+ORG 0x9e00
+
 jmp start
 
 ;Calls
@@ -86,26 +88,18 @@ mov si, error
 call println
 jmp loop
 
-cpl:
-db 0x0
+cpl db 0x0
 
-welcome:
-db 0xd, 0xa, "Welcome to EttinOS!", 0xd, 0xa, 0x0
+welcome db 0xd, 0xa, "Welcome to EttinOS!", 0xd, 0xa, 0x0
 
-prompt:
-db "> ", 0x0
+prompt db "> ", 0x0
 
 cmd:
-.echo:
-db "echo", 0x0
-.hello:
-db "hello", 0x0
-.help:
-db "help", 0x0
-.keycode:
-db "keycode", 0x0
-error:
-db "Unknown command", 0x0
+.echo    db "echo", 0x0
+.hello   db "hello", 0x0
+.help    db "help", 0x0
+.keycode db "keycode", 0x0
 
-buffer:
-times 0xff db 0
+error db "Unknown command", 0x0
+
+buffer times 0xff db 0
diff --git a/make.sh b/make.sh
index ffa2d71..8ae9905 100755
--- a/make.sh
+++ b/make.sh
@@ -1,11 +1,18 @@
 #!/bin/bash
 
 cd SOURCE/
-nasm BOOT.ASM -f bin -o ../BOOT.BIN
+
+if [ "$1" == "-F1440" ]
+    then nasm BOOT.ASM -d F1440 -f bin -o ../BOOT.BIN
+    else nasm BOOT.ASM -f bin -o ../BOOT.BIN
+fi
 nasm SYSTEM.ASM -f bin -o ../SYSTEM.BIN
 
 cd ..
 rm -f EttinOS.img
-mkfs.fat -C EttinOS.img 1440
+if [ "$1" == "-F1440" ]
+    then mkfs.fat -C EttinOS.img 1440
+    else mkfs.fat -C EttinOS.img 360
+fi
 dd if=BOOT.BIN of=EttinOS.img conv=notrunc bs=512 count=1
 mcopy -i EttinOS.img SYSTEM.BIN ::