Reorganise and comment the code and rewrite readstr.

make.sh

@@ -1,5 +1,10 @@
 #!/bin/bash
 
+if [ ! -d "build" ];
+then
+    mkdir build
+fi
+
 cd src/
 nasm boot.asm -f bin -o ../build/boot.bin
 nasm os.asm -f bin -o ../build/os.bin

src/boot.asm

@@ -1,23 +1,31 @@
 [ORG 0x7c00]
-mov ax, 0
-mov ds, ax
 jmp 0:start
+
 start:
 
+;Initialise ds
+mov ax, 0x0
+mov ds, ax
+
+;Set the source
+mov dh, 0x0
+mov ch, 0x0
+mov cl, 0x2
+;Set the destination
 mov ax, 0x1000
 mov es, ax
 mov bx, 0
-
+;Set the size
 mov al, 0x20
-mov dh, 0
-mov ch, 0
-mov cl, 0x2
-
+;Load
 mov ah, 0x2
 int 0x13
 
+;Boot
 jmp 0x1000:0
 
+;Padding
 times 0x1fe-($-$$) db 0
-db 0x55
-db 0xaa
+
+;Boot signature
+dw 0xaa55

src/byte2hexstr.inc

@@ -0,0 +1,32 @@
+;Converts a byte in ah to a hex string at di.
+
+byte2hexstr:
+
+;Set a key for the hex digits
+mov si, .key
+
+;Set a counter for the two characters of the hex string
+mov cx, 0x2
+
+.loop:
+
+;Read the byte
+rol ax, 0x4
+mov bx, ax
+
+;Convert the byte to a hex digit
+and bx, 0xf
+mov bl, [si + bx]
+
+;Store the hex digit
+mov [di], bl
+
+;Repeat
+inc di
+dec cx
+jnz .loop
+
+ret
+
+.key:
+db "0123456789abcdef"

src/calls.inc

@@ -1,193 +0,0 @@
-printstr:
-lodsb
-cmp al, 0
-je .done
-mov ah, 0xe
-int 0x10
-jmp printstr
-.done:
-ret
-
-readstr:
-mov di, readstr.out
-mov cx, 0x80
-mov al, 0
-rep stosb
-mov bl, 0
-mov ah, 0x3
-int 0x10
-mov byte [.lastln], dh
-mov di, readstr.out
-.loop:
-mov ah, 0
-int 0x16
-cmp al, 0
-je .loop
-cmp al, 0xd
-je .return
-cmp al, 0x8
-je .backspace
-cmp bl, 0x80
-je .loop
-cmp al, 0x9
-je .erase
-cmp al, 0x20
-je .space
-.char:
-mov byte [di], 0
-mov ah, 0xe
-int 0x10
-stosb
-inc bl
-jmp .checkln
-.erase:
-mov al, 0x20
-jmp .char
-.space:
-cmp byte [di], 0
-je .char
-mov al, byte [di]
-mov ah, 0xe
-int 0x10
-inc di
-inc bl
-.checkln:
-mov ah, 0x3
-int 0x10
-cmp dh, [.lastln]
-jle .loop
-mov byte [.lastln], dh
-jmp .loop
-.backspace:
-cmp bl, 0
-je .loop
-mov ah, 0x3
-int 0x10
-cmp dl, 1
-je .prevln
-mov ah, 0xe
-int 0x10
-dec di
-dec bl
-jmp .loop
-.prevln:
-mov ah, 0x2
-dec dh
-mov dl, [cpl]
-int 0x10
-dec di
-dec bl
-jmp .loop
-.return:
-mov di, readstr.end
-.findtrailing:
-dec di
-cmp byte [di], 0
-je .findtrailing
-cmp byte [di], 0x20
-je .deltrailing
-jmp .done
-.deltrailing:
-mov al, 0
-stosb
-dec di
-jmp .findtrailing
-.done:
-mov ah, 0x2
-mov dh, [.lastln]
-int 0x10
-mov si, newline
-call printstr
-ret
-.lastln:
-db 0
-.out:
-times 0x80 db 0
-.end:
-db 0
-
-cmpstr:
-mov al, [si]
-mov bl, [di]
-cmp al, bl
-jne .neq
-cmp al, 0
-je .eq
-inc si
-inc di
-jmp cmpstr
-.neq:
-clc
-ret
-.eq:
-stc
-ret
-
-byte2hexstr:
-mov di, .out
-mov si, .key
-mov cx, 0x2
-.loop:
-rol ax, 0x4
-mov bx, ax
-and bx, 0xf
-mov bl, [si + bx]
-mov [di], bl
-inc di
-dec cx
-jnz .loop
-ret
-.key:
-db "0123456789abcdef"
-.out:
-times 3 db 0
-
-help:
-mov si, .out
-call printstr
-ret
-.out:
-db "Input:", 0xd, 0xa, "* Typing a character overwrites the cursor location.", 0xd, 0xa, "* The tab key erases the cursor location.", 0xd, 0xa, "* The space and backspace keys move the cursor.", 0xd, 0xa, "Commands:", 0xd, 0xa, "* help: you are reading it.", 0xd, 0xa, "* hello: a hello world program.", 0xd, 0xa, "* echo: echoes its input.", 0xd, 0xa, "* keycode: echoes the BIOS code of a key.", 0xd, 0xa, 0
-
-hello:
-mov si, .out
-call printstr
-ret
-.out:
-db "Hello world!", 0xd, 0xa, 0
-
-echo:
-call readstr
-cmp byte [readstr.out], 0
-je .done
-mov si, readstr.out
-call printstr
-mov si, newline
-call printstr
-.done:
-ret
-
-keycode:
-mov ah, 0
-int 0x16
-mov byte [.scan], ah
-mov byte [.ascii], al
-mov si, .prefix
-call printstr
-mov ah, [.scan]
-call byte2hexstr
-mov si, byte2hexstr.out
-call printstr
-mov ah, [.ascii]
-call byte2hexstr
-mov si, byte2hexstr.out
-call printstr
-mov si, newline
-call printstr
-ret
-.prefix:
-db "0x", 0
-.scan:
-db 0
-.ascii:
-db 0

src/cmpstr.inc

@@ -0,0 +1,32 @@
+;Compares strings from si and di and sets the carry flag if they are equal and clears it if not.
+
+cmpstr:
+
+;Load characters
+mov al, [si]
+mov bl, [di]
+
+;Compare the characters
+cmp al, bl
+
+;Check for difference
+jne .neq
+
+;Check for the string end
+cmp al, 0x0
+je .eq
+
+;Repeat
+inc si
+inc di
+jmp cmpstr
+
+.neq:
+;Clear the carry flag
+clc
+ret
+
+.eq:
+;Set the carry flag
+stc
+ret

src/echo.inc

@@ -0,0 +1,19 @@
+;Reads a string to the buffer and prints it.
+
+echo:
+
+;Read a string
+mov di, buffer
+mov al, 0xff
+call readstr
+
+;Check for an empty string
+cmp byte [buffer], 0x0
+je .done
+
+;Print the string
+mov si, buffer
+call println
+
+.done:
+ret

src/hello.inc

@@ -0,0 +1,11 @@
+;Prints a hello world.
+
+hello:
+
+mov si, .hello
+call println
+
+ret
+
+.hello:
+db "Hello world!", 0x0

src/help.inc

@@ -0,0 +1,11 @@
+;Prints help.
+
+help:
+
+mov si, .help
+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

src/keycode.inc

@@ -0,0 +1,44 @@
+;Reads a keypress and prints its keycode.
+
+keycode:
+
+;Read a keypress
+mov ah, 0x0
+int 0x16
+
+;Store the keycode
+mov [.scan], ah
+mov [.ascii], al
+
+;Print the prefix
+mov si, .prefix
+call printstr
+
+;Convert the scancode to a hex string
+mov ah, [.scan]
+mov di, .keycode
+call byte2hexstr
+
+;Convert the ascii value to a hex string
+mov ah, [.ascii]
+mov di, .keycode
+add di, 0x2
+call byte2hexstr
+
+;Print the keycode
+mov si, .keycode
+call println
+
+ret
+
+.prefix:
+db "0x", 0x0
+
+.scan:
+db 0x0
+
+.ascii:
+db 0x0
+
+.keycode:
+times 0x5 db 0x0

src/os.asm

@@ -1,79 +1,113 @@
 jmp start
 
-%include "calls.inc"
+;Calls
+%include "printstr.inc"
+%include "println.inc"
+%include "readstr.inc" ;Under construction
+%include "cmpstr.inc"
+%include "byte2hexstr.inc"
+
+;Commands
+%include "echo.inc"
+%include "hello.inc"
+%include "help.inc"
+%include "keycode.inc"
 
 start:
 
+;Initialise ds
 mov ax, 0x1000
 mov ds, ax
 
+;Get the terminal width
 mov ah, 0xf
 int 0x10
-mov byte [cpl], ah
+mov [cpl], ah
 
+;Print a welcome message
 mov si, welcome
-call printstr
+call println
 
 loop:
+
+;Print a prompt
 mov si, prompt
 call printstr
+
+;Read a command
+mov di, buffer
+mov al, 0xff
 call readstr
-cmp byte [readstr.out], 0
-je loop
+
 exec:
-.help:
-mov si, readstr.out
-mov di, cmd.help
-call cmpstr
-jnc .hello
-call help
-jmp loop
-.hello:
-mov si, readstr.out
-mov di, cmd.hello
-call cmpstr
-jnc .echo
-call hello
-jmp loop
+;No command
+cmp byte [buffer], 0x0
+je loop
 .echo:
-mov si, readstr.out
+;Check for the command
+mov si, buffer
 mov di, cmd.echo
 call cmpstr
-jnc .keycode
+jnc .hello
+;Execute the command
 call echo
 jmp loop
+.hello:
+;Check for the command
+mov si, buffer
+mov di, cmd.hello
+call cmpstr
+jnc .help
+;Execute the command
+call hello
+jmp loop
+.help:
+;Check for the command
+mov si, buffer
+mov di, cmd.help
+call cmpstr
+jnc .keycode
+;Execute the command
+call help
+jmp loop
 .keycode:
-mov si, readstr.out
+;Check for the command
+mov si, buffer
 mov di, cmd.keycode
 call cmpstr
 jnc .error
+;Execute the command
 call keycode
 jmp loop
 .error:
-mov si, cmd.error
-call printstr
+mov si, error
+call println
 jmp loop
 
 cpl:
-db 0
+db 0x0
 
 welcome:
-db 0xd, 0xa, "Welcome to EttinOS!", 0xd, 0xa, 0xd, 0xa, 0
+db 0xd, 0xa, "Welcome to EttinOS!", 0xd, 0xa, 0x0
 
 prompt:
-db "> ", 0
+db "> ", 0x0
 
 cmd:
-.help:
-db "help", 0
-.hello:
-db "hello", 0
 .echo:
-db "echo", 0
+db "echo", 0x0
+.hello:
+db "hello", 0x0
+.help:
+db "help", 0x0
 .keycode:
-db "keycode", 0
-.error:
-db "Unknown command", 0xd, 0xa, 0
+db "keycode", 0x0
 
-newline:
-db 0xd, 0xa, 0
+error:
+db "Unknown command", 0x0
+
+;buffer:
+;times 0x100 db 0
+
+buffer:
+times 0x100 db 0

src/println.inc

@@ -0,0 +1,14 @@
+;Prints a line from si until a null.
+println:
+
+;Print a string
+call printstr
+
+;Print a newline
+mov si, .newline
+call printstr
+
+ret
+
+.newline:
+db 0xd, 0xa, 0x0

src/printstr.inc

@@ -0,0 +1,20 @@
+;Prints a string from si until a null.
+
+printstr:
+
+;Load a character
+lodsb
+
+;Check for the string end
+cmp al, 0x0
+je .done
+
+;Print the character
+mov ah, 0xe
+int 0x10
+
+;Repeat
+jmp printstr
+
+.done:
+ret

src/readstr.inc

@@ -0,0 +1,177 @@
+;Reads a string of at most al characters to di.
+
+readstr:
+
+;Store the length
+mov [.length], al
+
+;Initialise the destination with spaces
+mov cx, [.length]
+mov al, 0x20
+rep stosb
+sub di, [.length]
+
+;Initialise the cursor pointer
+mov bl, 0x0
+
+;Initialise the last input line pointer
+mov ah, 0x3
+int 0x10
+mov byte [.lastln], dh
+
+.loop:
+
+;Read a keypress
+mov ah, 0x0
+int 0x16
+
+;Check for null
+cmp al, 0x0
+je .loop
+
+;Check for return
+cmp al, 0xd
+je .return
+
+;Check for backspace
+cmp al, 0x8
+je .backspace
+
+;Check for input end
+cmp bl, [.length]
+je .loop
+
+;Check for space
+cmp al, 0x20
+je .space
+
+;Check for erase
+cmp al, 0x9
+je .erase
+
+;Check for non-printing characters
+cmp al, 0x1f
+jle .loop
+cmp al, 0x7f
+je .loop
+
+.char:
+;Store the  character
+stosb
+;Print the character
+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
+jmp .loop
+
+.erase:
+;Replace the cursor position with a space
+mov al, 0x20
+jmp .char
+
+.space:
+;Get the cursor position
+mov ah, 0x3
+int 0x10
+;More 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
+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, 0x0
+je .loop
+;Get the cursor position
+mov ah, 0x3
+int 0x10
+;More 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
+jmp .loop
+
+.return:
+
+;Go to the end of the input
+mov bh, 0
+sub di, bx
+add di, [.length]
+
+.findtrailing:
+;Check for a trailing space
+dec di
+cmp byte [di], 0x20
+je .deltrailing
+jmp .done
+
+.deltrailing:
+;Delete a trailing space
+mov al, 0x0
+stosb
+dec di
+jmp .findtrailing
+
+.done:
+;Move the cursor to the last line of input
+mov ah, 0x2
+mov dh, [.lastln]
+int 0x10
+;Print a newline
+mov si, .newline
+call printstr
+
+ret
+
+.length:
+db 0x0
+
+.cursor:
+db 0x0
+
+.lastln:
+db 0x0
+
+.newline:
+db 0xd, 0xa, 0x0