Move the system to low memory and tweak readln.

make.sh

@@ -6,4 +6,3 @@ nasm system.asm -f bin -O0 -o ../system.bin
 
 cd ..
 cat boot.bin system.bin > EttinOS.img
-rm boot.bin system.bin

source/boot.asm

@@ -24,31 +24,37 @@ db "FAT12   "    ;File system type
 
 start:
 
-;Initialise ds
+;Set up the data segment
 mov ax, 0x0
 mov ds, ax
 
+;Set up the stack
+cli
+mov ax, 0x0
+mov ss, ax
+mov sp, 0x7c00
+sti
+
 ;Load the system
 ;Set the source
-mov dl, 0x0
 mov dh, 0x0
 mov ch, 0x0
 mov cl, 0x2
 ;Set the destination
-mov ax, 0x1000
+mov ax, 0x0
 mov es, ax
-mov bx, 0x200
+mov bx, 0x7e00
 ;Set the size
-mov al, 0x20
+mov al, 0x5
 ;Load
 mov ah, 0x2
 int 0x13
 
 ;Boot the system
-jmp 0x1000:0x200
+jmp 0x0:0x7e00
 
 ;Padding
-times 0x1fe-($-$$) db 0
+times 0x1fe-($-$$) db 0x0
 
 ;Boot signature
 dw 0xaa55

source/readln.inc

@@ -2,14 +2,17 @@
 
 readln:
 
-;Store the length
-mov [.length], al
+;Store the input length in the stack
+mov ah, 0
+push ax
 
 ;Initialise the destination with spaces
-mov cx, [.length]
+mov cx, ax
 mov al, 0x20
 rep stosb
-sub di, [.length]
+pop ax
+push ax
+sub di, ax
 
 ;Initialise the cursor pointer
 mov bl, 0x1
@@ -34,7 +37,9 @@ cmp al, 0x8
 je .backspace
 
 ;Check for input end
-cmp bl, [.length]
+pop dx
+push dx
+cmp bl, dl
 je .loop
 
 ;Check for space
@@ -59,16 +64,7 @@ mov ah, 0xe
 int 0x10
 ;Move the cursor pointer
 inc bl
-
-.checkln:
-;Get the cursor position
-mov ah, 0x3
-int 0x10
-;Check if the current line is the last one of the input
-cmp dh, [.lastln]
-jle .loop
-;If it is mark it as so
-mov byte [.lastln], dh
+call .checkln
 jmp .loop
 
 .erase:
@@ -77,55 +73,14 @@ mov al, 0x20
 jmp .char
 
 .space:
-;Get the cursor position
-mov ah, 0x3
-int 0x10
-;Move from the end of a line to the beginning of the next one
-cmp dl, [cpl]
-je .nextln
-;Move forward within a line
-inc dl
-mov ah, 0x2
-int 0x10
-inc di
-inc bl
+call .nextchar
 jmp .loop
 
-.nextln:
-mov ah, 0x2
-inc dh
-mov dl, 0x1
-int 0x10
-inc di
-inc bl
-;Go to the last input line check
-jmp .checkln
-
 .backspace:
 ;Check for the input beginning
 cmp bl, 0x1
 je .loop
-;Get the cursor position
-mov ah, 0x3
-int 0x10
-;Move from the beginning of a line to the end of the previous one
-cmp dl, 0x1
-je .prevln
-;Move backward within a line
-dec dl
-mov ah, 0x2
-int 0x10
-dec di
-dec bl
-jmp .loop
-
-.prevln:
-mov ah, 0x2
-dec dh
-mov dl, [cpl]
-int 0x10
-dec di
-dec bl
+call .prevchar
 jmp .loop
 
 .return:
@@ -133,7 +88,8 @@ jmp .loop
 ;Go to the end of the input
 mov bh, 0x0
 sub di, bx
-add di, [.length]
+pop ax
+add di, ax
 
 .findtrailing:
 ;Check for a trailing space
@@ -158,11 +114,69 @@ call newline
 
 ret
 
-.length:
-db 0x0
-
-.cursor:
-db 0x0
-
 .lastln:
 db 0x0
+
+.nextchar:
+;Get the cursor position
+mov ah, 0x3
+int 0x10
+;Move from the end of a line to the beginning of the next one
+cmp dl, [cpl]
+je .nextln
+;Move forward within a line
+inc dl
+mov ah, 0x2
+int 0x10
+inc di
+inc bl
+ret
+
+.nextln:
+mov ah, 0x2
+inc dh
+mov dl, 0x1
+int 0x10
+inc di
+inc bl
+;Go to the last input line check
+call .checkln
+ret
+
+.prevchar:
+;Get the cursor position
+mov ah, 0x3
+int 0x10
+;Move from the beginning of a line to the end of the previous one
+cmp dl, 0x1
+je .prevln
+;Move backward within a line
+dec dl
+mov ah, 0x2
+int 0x10
+dec di
+dec bl
+ret
+
+.prevln:
+mov ah, 0x2
+dec dh
+mov dl, [cpl]
+int 0x10
+dec di
+dec bl
+ret
+
+.checkln:
+;Get the cursor position
+mov ah, 0x3
+int 0x10
+;Check if the current line is the last one of the input
+cmp dh, [.lastln]
+jg .markln
+ret
+
+.markln:
+;Mark the current line as the last one of the input
+mov byte [.lastln], dh
+ret

source/system.asm

@@ -1,4 +1,4 @@
-[ORG 0x200]
+[ORG 0x7e00]
 jmp start
 
 ;Calls
@@ -17,17 +17,6 @@ jmp start
 
 start:
 
-;Initialise ds
-mov ax, 0x1000
-mov ds, ax
-
-;Set up the stack
-cli
-mov ax, 0x1000
-mov ss, ax
-mov sp, 0x200
-sti
-
 ;Get the terminal width
 mov ah, 0xf
 int 0x10