Improve clarity; Trap long input

1 files changed, 53 insertions, 41 deletions

diff --git a/terminal.asm b/terminal.asm
index b3beb7c..13ed786 100644
--- a/terminal.asm
+++ b/terminal.asm
@@ -1,64 +1,76 @@
 %ifndef _TERMINAL_ASM
 %define _TERMINAL_ASM
 
-MAXBUF equ 254
+T_BUFSZ equ 256					; maximum length of terminal input buffer
 
 terminal:
 	push bp
 	mov bp, sp
-	;sub sp, MAXBUF		; allocate large string buffer
-	
+
 	.clear_buffer:
-		mov cx, MAXBUF
-		mov bx, t_buffer
-		mov di, bx
+		mov cx, T_BUFSZ			; counter is length of buffer
+		mov bx, t_buffer		; get address of buffer
+		mov di, bx			; destination is buffer
 		.cl:
-			mov [di], byte 0
-			inc di
-			dec cx
-			jne .cl
-		mov di, bx
-
-	.do_prompt:	
-		mov cx, 0
+			mov [di], byte 0	; zero out
+			inc di			; increment buffer address
+			dec cx			; decrement counter
+			jne .cl			; repeat until counter is 0
+
+		mov di, bx			; reset destination to original address
+
+	.do_prompt:
+		mov cx, 0			; reset counter
+						; this tracks keyboard presses
 		mov al, CR
-		call putc
+		call putc			; write carriage return to console
+
+		push t_msg_prompt		; address of prompt string
+		push t_msg_prompt_fmt		; address of prompt format string
+		call printf			; print prompt to console
+		add sp, 4			; clean up stack
 
-		push t_msg_prompt
-		push t_msg_prompt_fmt
-		call printf
-		add sp, 4
-	
-	mov di, t_buffer	
+	mov di, t_buffer			; input destination is buffer
 	.read_command:
-		call kbd_read
+		call kbd_read			; get input from user
 		.update_buffer:
 			cmp al, CR
-			je .dump_buffer
-			stosb
-			inc cx
+			je .flush_buffer	; if carriage return, flush buffer
+
+			cmp cx, T_BUFSZ
+			jge .read_command	; trap lines to long to fit in memory
+						; we cannot continue until user hits return
 
-			jmp .output
+			stosb			; write input character to buffer
+			inc cx			; increment character count
 
-		.dump_buffer:
-			cmp [di-1], byte 0
-			je .do_prompt
+			jmp .output		; output character (default)
+
+		.flush_buffer:
+			cmp [di-1], byte 0	; stosb above increments di.
+						; (di - 1) is the previous input
+			je .do_prompt		; if no input (null), start over
 
 			mov al, CR
-			call putc
-
-			push t_buffer			; push onto stack
-			push t_buffer_fmt
-			call printf		; write out string
-			add sp, 4
-	
-			jmp .clear_buffer
-			
+			call putc		; print carriage return
+
+			; ---- TEMPORARY ---
+			; A jump to a command parser occur here eventually
+			; TODO: write string tokenizer
+
+			push t_buffer		; push buffer string address
+			push t_buffer_fmt	; push buffer format string address
+			call printf		; write input to console
+			add sp, 4		; clean up stack
+			; --- END TEMPORARY ---
+
+			jmp .clear_buffer	; zero out buffer / start over
+
 	.output:
 		call putc
-		jmp .read_command
+		jmp .read_command		; print input to screen as we type
 
-	jmp .do_prompt
+	jmp .do_prompt				; start over
 
 	mov sp, bp
 	pop bp
@@ -68,6 +80,6 @@ terminal:
 t_msg_prompt_fmt: db '%s', 0
 t_msg_prompt: db '$ ', 0
 t_buffer_fmt: db '%s', 0
-t_buffer: times MAXBUF db 0
+t_buffer: times T_BUFSZ db 0
 
 %endif