debug rom: implement cmd loop

rom/debug.asm

@@ -1,8 +1,6 @@
 	cpu 8086
 	org 0x0000
 
-stacksize: equ 0x20
-
 	db 0x55, 0xAA
 	db 0x00
 	jmp init
@@ -43,11 +41,8 @@ init:	push ds
 	; load DS for
 	mov ds, ax
 
-	mov al, [cs:2]
-	inc ax
-	shr ax, 1
 	; move down int 0x12 ptr to make space for us
-	sub [0x413], ax
+	sub word [0x413], ((end - $$) >> 10)
 	; calculate segment from kilobytes
 	mov ax, [0x413]
 	mov cl, 6
@@ -141,7 +136,6 @@ printregs:
 .fskip: shl dx, 1
 	loop .floop
 	call space
-	call crlf
 	ret
 
 int3entry:
@@ -170,13 +164,35 @@ int3entry:
 	mov [reg_ss], ss
 	mov [reg_es], es
 	; initialize other segments and setup stack
+	mov ax, cs
 	mov es, ax
 	mov ss, ax
-	mov sp, (stack+stacksize)
+	mov sp, end
 	call crlf
 
 	call printregs
 
+loop:	; new line & show prompt
+	call crlf
+	mov al, '-'
+	int 0x10
+	; read data
+	call read
+	jc loop
+	; execute
+	call crlf
+	mov al, [cmdbuf]
+	call runcmd
+	jmp loop
+
+runcmd:	cmp al, 'r'
+	je printregs
+	; print a question mark
+	xor bx, bx
+	mov ax, 0x0e3F
+	int 0x10
+	ret
+
 return:	; restore stack pointer
 	mov ss, [reg_ss]
 	mov sp, [reg_sp]
@@ -202,11 +218,47 @@ return:	; restore stack pointer
 	iret
 
 names:	db "AXCXDXBXSPBPSIDI"
-	db "DSESSSCSIPFL"
+	db "ESCSSSDSIPFL"
 
 fnames:	db "++++ODIT"
 	db "SZ+A+P+C"
 
+getc:	xor ax, ax
+	int 0x16
+	test al, al
+	jz getc
+	ret
+
+read:	mov di, cmdbuf
+.loop:	call getc
+	cmp al, 0x03
+	je .can
+	cmp al, 0x0D
+	je .enter
+	cmp al, 0x08
+	je .bs
+	cmp di, cmdbuf+cmdlen
+	jnc .loop
+	stosb
+	mov ah, 0x0e
+	xor bx, bx
+	int 0x10
+	jmp .loop
+	ret
+.bs:	cmp di, cmdbuf
+	jbe .loop
+	xor bx, bx
+	mov ax, 0x0e08
+	int 0x10
+	mov al, 0x20
+	int 0x10
+	mov al, 0x08
+	int 0x10
+	dec di
+	jmp .loop
+.can:	stc
+.enter:	ret
+
 codeend:
 
 reg_ax:	dw 0
@@ -226,6 +278,10 @@ reg_ds:	dw 0
 reg_ip:	dw 0
 reg_fl:	dw 0
 
-stack:	times stacksize dw 0
+cmdlen:	equ 16
+cmdbuf:	times cmdlen dw 0
 
-align 512
+stack:	times 0x80 dw 0
+
+align 1024
+end: