debug: Rework repl loop and implement help command '?'

rom/debug.asm

@@ -58,18 +58,30 @@ init:	push ds
 	pop ds
 	retf
 
-crlf:	xor bx, bx
-	mov ax, 0x0e0a
-	int 0x10
-	mov al, 0x0d
+	; Print AL
+space:	mov al, ' '
+putc:	xor bx, bx
+	mov ah, 0x0e
 	int 0x10
 	ret
 
-space:	xor bx, bx
-	mov ax, 0x0e20
-	int 0x10
+	; Print CS:SI
+puts:	push ds
+	push cs
+	pop ds
+.loop:	lodsb
+	test al, al
+	jz .ret
+	call putc
+	jmp .loop
+.ret:	pop ds
 	ret
 
+crlf:	mov al, 0x0A
+	call putc
+	mov al, 0x0D
+	jmp putc
+
 print16:
 	; setup bx and ah for int 10h call
 	xor bx, bx
@@ -94,42 +106,6 @@ print16:
 .noadj:	int 0x10
 	ret
 
-printregs:
-	mov cx, 13
-	xor bx, bx
-	mov ah, 0x0e
-	mov si, reg_ax
-.loop:	push cx
-	mov dx, [cs:si+names]
-	mov al, dl
-	int 0x10
-	mov al, dh
-	int 0x10
-	mov al, '='
-	int 0x10
-	lodsw
-	mov dx, ax
-	call print16
-	call space
-	pop cx
-	loop .loop
-
-	mov dx, [reg_fl]
-	mov si, fnames
-	mov cx, 16
-.floop:	mov al, [cs:si]
-	inc si
-	cmp al, '+'
-	je .fskip
-	test dx, 0x8000
-	jnz .fprnt
-	mov al, '-'
-.fprnt: int 0x10
-.fskip: shl dx, 1
-	loop .floop
-	call space
-	ret
-
 int3entry:
 	; save DS and AX
 	push ds
@@ -168,42 +144,21 @@ int3entry:
 	mov ss, ax
 	mov sp, stack
 	call crlf
-
 	call printregs
 
-	mov dx, ds
-	call print16
-
-loop:	; new line & show prompt
-	call crlf
+loop:	; show prompt
 	mov al, '-'
 	int 0x10
 	; read data
 	call read
+	pushf
+	call crlf
+	popf
 	jc loop
 	; execute
-	call crlf
-	mov al, [cmdbuf]
 	call runcmd
 	jmp loop
 
-runcmd:	cmp al, 'r'
-	je printregs
-	cmp al, 'g'
-	je go
-	cmp al, 't'
-	je step
-	; print a question mark
-	xor bx, bx
-	mov ax, 0x0e3F
-	int 0x10
-	ret
-
-go:	and word [reg_fl+1], 0xfe
-	jmp return
-
-step:	or word [reg_fl+1], 0x03
-
 return:	; restore stack pointer
 	mov ss, [reg_ss]
 	mov sp, [reg_sp]
@@ -276,6 +231,75 @@ read:	mov di, cmdbuf
 .can:	stc
 .enter:	ret
 
+runcmd:	mov al, [cmdbuf]
+	cmp al, 'g'
+	je cmd_g
+	cmp al, 'r'
+	je cmd_r
+	cmp al, 't'
+	je cmd_t
+	cmp al, '?'
+	je cmd_?
+	mov al, '?'
+	call putc
+	jmp crlf
+
+cmd_?:	mov si, .txt
+	jmp puts
+.txt:	db "g       Go", 0x0A, 0x0D
+	db "r       Print register values", 0x0A, 0x0D
+	db "t       Single-Step", 0x0A, 0x0D
+	db 0
+
+cmd_g:	and word [reg_fl+1], 0xfe
+	jmp return
+
+cmd_r:	jmp printregs
+
+cmd_t:	or word [reg_fl+1], 0x03
+	jmp return
+
+printregs:
+	mov cx, 13
+	xor bx, bx
+	mov ah, 0x0e
+	mov si, reg_ax
+.loop:	push cx
+	mov dx, [cs:si+names]
+	lodsw
+	call printreg
+	pop cx
+	loop .loop
+
+	mov dx, [reg_fl]
+	mov si, fnames
+	mov cx, 16
+.floop:	mov al, [cs:si]
+	inc si
+	cmp al, '+'
+	je .fskip
+	test dx, 0x8000
+	jnz .fprnt
+	mov al, '-'
+.fprnt: int 0x10
+.fskip: shl dx, 1
+	loop .floop
+	call crlf
+	ret
+
+printreg:
+	push ax
+	mov al, dl
+	call putc
+	mov al, dh
+	call putc
+	mov al, '='
+	call putc
+	pop dx
+	call print16
+	call space
+	ret
+
 	align 512
 
 absolute 0