debug: Add stub for instruction decoding

debug/asm.asm

@@ -0,0 +1,9 @@
+
+	; Prints instruction at ES:BX in human-readable form
+disasm:	call print_esbx
+	call space
+	mov si, instr.db
+	call putcs
+	call crlf
+	ret
+

debug/chario.asm

@@ -28,7 +28,20 @@ crlf:	mov al, 0x0A
 	mov al, 0x0D
 	jmp putc
 
-print16:
+print_dl:
+	mov cl, 4
+	; repeat 2 times
+	call .c
+.c:	mov al, dl
+	shl dx, cl
+	shr al, cl
+	add al, 0x30
+	cmp al, 0x3a
+	jl putc
+	add al, 7
+	jmp putc
+
+print_dx:
 	mov cl, 4
 	; this double-call is essentially a 4 times repeating loop
 	call .c1
@@ -48,6 +61,19 @@ print16:
 	add al, 7
 	jmp putc
 
+print_esbx:
+	push cx
+	push dx
+	mov dx, es
+	call print_dx
+	mov al, ':'
+	call putc
+	mov dx, bx
+	call print_dx
+	pop dx
+	pop cx
+	ret
+
 	; Read character
 getc:	xor ax, ax
 	int 0x16

debug/edit.asm

@@ -52,7 +52,7 @@ printreg:
 	mov al, '='
 	call putc
 	pop dx
-	call print16
+	call print_dx
 	call space
 	ret
 
@@ -60,7 +60,7 @@ printreg:
 edit_word:
 	push bx
 	mov dx, [es:bx]
-	call print16
+	call print_dx
 	mov al, '.'
 	call putc
 	mov byte [inmin], 4

debug/names.asm

@@ -8,3 +8,6 @@ fnames:	; control flags
 	db "++++ODIT"
 	; status flags
 	db "SZ+A+P+C"
+
+instr:
+.db:	db "DB", 0

debug/run.asm

@@ -40,6 +40,11 @@ int3entry:
 	mov sp, stack
 	call crlf
 	call printregs
+	push es
+	mov es, [reg_cs]
+	mov bx, [reg_ip]
+	call disasm
+	pop es
 
 loop:	; show prompt
 	mov al, '-'

debug/util.asm

@@ -14,12 +14,12 @@ cmd_h:	call eat_whitespace
 
 	push dx
 	add dx, bx
-	call print16
+	call print_dx
 	call space
 	pop dx
 
 	sub dx, bx
-	call print16
+	call print_dx
 
 	jmp crlf
 .err:	mov di, eat_hex_word.emsg

rom/debug.asm

@@ -81,6 +81,7 @@ cerr:	mov al, '?'
 	%include "debug/edit.asm"
 	%include "debug/run.asm"
 	%include "debug/util.asm"
+	%include "debug/asm.asm"
 
 	align 512