Add readch and for the sake of symmetry printch, simplify make.sh, and tweak the code a bit to make it more consistent.

SOURCE/BOOT.ASM

@@ -1,9 +1,9 @@
 [ORG 0x7c00]
-jmp short start
+jmp start
 nop
 
 ;1.44 MB 3.5" floppy disk description table
-OEMLabel          db "EttinOS "
+OEMLabel          db "ETTINOS "
 BytesPerSector    dw 0x200
 SectorsPerCluster db 0x1
 BootRecordSectors dw 0x1
@@ -19,7 +19,7 @@ LargeSectors      dd 0x0
 DriveNumber       dw 0x0
 DriveSignature    db 0x29
 VolumeID          dd 0x0
-VolumeLabel       db "EttinOS    "
+VolumeLabel       db "ETTINOS    "
 FileSystem        db "FAT12   "
 
 start:
@@ -53,7 +53,7 @@ mov al, 0xe
 mov ah, 0x2
 int 0x13
 
-;Search the root FAT for the system
+;Search the root FAT for the system FAT
 ;Set DI to the root FAT
 mov ax, ds
 mov es, ax
@@ -64,7 +64,7 @@ mov ax, 0x0
 search:
 ;Store CX in the stack
 push cx
-;Check for the binary
+;Check for the system FAT
 mov si, sysfile
 mov cx, 0xb
 rep cmpsb
@@ -79,7 +79,7 @@ loop search
 
 ;Load the system FAT
 loadsysfat:
-;???
+;Store the first cluster
 mov ax, word [es:di+0xf]
 mov word [cluster], ax
 ;Set the source

SOURCE/BYTE2HEX.INC

@@ -1,4 +1,4 @@
-;Converts a byte in ah to a hex string at di.
+;Converts a byte in AH to a hex string at DI.
 
 byte2hex:
 
@@ -8,16 +8,16 @@ pusha
 ;Set a key for the hex digits
 mov si, .key
 
-;Set a counter for the two characters of the hex string
+;Set a counter for the two hex digits
 mov cx, 0x2
 
 .loop:
 
-;Read the byte
+;Read a nibble
 rol ax, 0x4
 mov bx, ax
 
-;Convert the byte to a hex digit
+;Convert the nibble to a hex digit
 and bx, 0xf
 mov bl, [si + bx]
 

SOURCE/CMPSTR.INC

@@ -1,4 +1,4 @@
-;Compares strings from si and di and sets the carry flag if they are equal and clears it if not.
+;Compares strings from SI and SI and sets the carry flag if they are equal and clears it if not.
 
 cmpstr:
 
@@ -40,4 +40,4 @@ stc
 ;Load the initial registers from the stack
 popa
 
-ret
+ret

SOURCE/ECHO.INC

@@ -16,4 +16,4 @@ mov si, buffer
 call println
 
 .done:
-ret
+ret

SOURCE/HELP.INC

@@ -8,4 +8,4 @@ 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
+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

SOURCE/KEYCODE.INC

@@ -1,4 +1,4 @@
-;Reads a keypress and prints its BIOS code.
+;Reads a keypress and prints its BIOS keycode.
 
 keycode:
 

SOURCE/PRINTCH.INC

@@ -0,0 +1,8 @@
+;Prints a character from AL
+
+printch:
+
+mov ah, 0xe
+int 0x10
+
+ret

SOURCE/PRINTLN.INC

@@ -1,4 +1,4 @@
-;Prints a string from si until a null, followed by a newline.
+;Prints a string from SI until a null, followed by a newline.
 
 println:
 

SOURCE/PRINTSTR.INC

@@ -1,4 +1,4 @@
-;Prints a string from si until a null.
+;Prints a string from SI until a null.
 
 printstr:
 
@@ -16,7 +16,6 @@ je .done
 
 ;Print the character
 mov ah, 0xe
-mov bx, 0x0
 int 0x10
 
 ;Repeat

SOURCE/READCH.INC

@@ -0,0 +1,29 @@
+;Reads a character to AL
+
+readch:
+
+;Store the initial registers
+push bx
+push ax
+
+;Read a keypress
+mov ah, 0x0
+int 0x16
+
+;Check for non-printing characters
+cmp al, 0x1f
+jle readch
+cmp al, 0x7f
+je readch
+
+;Print the character
+mov ah, 0xe
+int 0x10
+
+;Load the initial registers
+pop bx
+mov ah, bh
+pop bx
+
+.done:
+ret

SOURCE/READLN.INC

@@ -1,4 +1,4 @@
-;Reads a string of at most al characters to di until a return and prints a newline.
+;Reads a string of at most AL characters to DI until a return and prints a newline.
 
 readln:
 

SOURCE/READSTR.INC

@@ -1,4 +1,4 @@
-;Reads a string of at most al characters to di until a return.
+;Reads a string of at most AL characters to DI until a return.
 
 readstr:
 
@@ -29,32 +29,27 @@ int 0x16
 ;Check for return
 cmp al, 0xd
 je .return
-
 ;Check for backspace
 cmp al, 0x8
 je .backspace
-
 ;Check for input end
 pop dx
 push dx
 cmp bl, dl
 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:
+.character:
 ;Store the  character
 stosb
 ;Print the character
@@ -67,7 +62,7 @@ jmp .loop
 .erase:
 ;Replace the cursor position with a space
 mov al, 0x20
-jmp .char
+jmp .character
 
 .space:
 call .nextchar
@@ -86,19 +81,18 @@ jmp .loop
 
 .return:
 
+;Find and remove trailing spaces
 ;Go to the end of the input
 pop ax
 mov bh, 0x0
 sub ax, bx
 push di
 add di, ax
-
 .findtrailing:
 ;Check for a trailing space
 cmp byte [di], 0x20
 je .deltrailing
 jmp .end
-
 .deltrailing:
 ;Delete a trailing space
 mov al, 0x0
@@ -106,8 +100,8 @@ stosb
 sub di, 0x2
 jmp .findtrailing
 
-.end:
 ;Move the cursor to the end of the input string
+.end:
 pop di
 .findend:
 cmp byte [di], 0x0
@@ -138,7 +132,6 @@ inc dl
 mov ah, 0x2
 int 0x10
 ret
-
 .nextln:
 mov ah, 0x2
 inc dh
@@ -158,7 +151,6 @@ dec dl
 mov ah, 0x2
 int 0x10
 ret
-
 .prevln:
 mov ah, 0x2
 dec dh

SOURCE/SYSTEM.ASM

@@ -2,13 +2,15 @@
 jmp start
 
 ;Calls
+%include "BYTE2HEX.INC"
+%include "CMPSTR.INC"
 %include "PRINTNL.INC"
+%include "PRINTCH.INC"
 %include "PRINTSTR.INC"
 %include "PRINTLN.INC"
+%include "READCH.INC"
 %include "READSTR.INC"
 %include "READLN.INC"
-%include "CMPSTR.INC"
-%include "BYTE2HEX.INC"
 
 ;Commands
 %include "ECHO.INC"
@@ -38,13 +40,11 @@ mov di, buffer
 mov al, 0xff
 call readln
 
-exec:
 ;Identify and execute the command
-
+exec:
 ;Check for no command
 cmp byte [buffer], 0x0
 je loop
-
 .echo:
 ;Check
 mov si, buffer
@@ -54,7 +54,6 @@ jnc .hello
 ;Execute
 call echo
 jmp loop
-
 .hello:
 ;Check
 mov si, buffer
@@ -64,7 +63,6 @@ jnc .help
 ;Execute
 call hello
 jmp loop
-
 .help:
 ;Check
 mov si, buffer
@@ -74,7 +72,6 @@ jnc .keycode
 ;Execute
 call help
 jmp loop
-
 .keycode:
 ;Check
 mov si, buffer
@@ -84,7 +81,6 @@ jnc .error
 ;Execute
 call keycode
 jmp loop
-
 .error:
 mov si, error
 call println
@@ -108,7 +104,6 @@ db "hello", 0x0
 db "help", 0x0
 .keycode:
 db "keycode", 0x0
-
 error:
 db "Unknown command", 0x0
 

make.sh

@@ -1,14 +1,11 @@
 #!/bin/bash
 
 cd SOURCE/
-nasm BOOT.ASM -f bin -O0 -o ../BOOT.BIN
-nasm SYSTEM.ASM -f bin -O0 -o ../SYSTEM.BIN
+nasm BOOT.ASM -f bin -o ../BOOT.BIN
+nasm SYSTEM.ASM -f bin -o ../SYSTEM.BIN
 
 cd ..
-if [[ -f EttinOS.img ]]
-then
-    rm EttinOS.img
-fi
+rm -f EttinOS.img
 mkfs.fat -C EttinOS.img 1440
-mcopy -i EttinOS.img SYSTEM.BIN ::
 dd if=BOOT.BIN of=EttinOS.img conv=notrunc bs=512 count=1
+mcopy -i EttinOS.img SYSTEM.BIN ::