From 04a7087d79c1965c734799ed9f7e1b88f9004aa8 Mon Sep 17 00:00:00 2001
From: Ain <41307858+nero@users.noreply.github.com>
Date: Tue, 19 May 2020 23:10:20 +0200
Subject: [PATCH] debug: First steps on instruction decoding

---
 debug/asm.asm   | 96 ++++++++++++++++++++++++++++++++++++++++++++++---
 debug/edit.asm  |  9 +++++
 debug/names.asm |  9 ++++-
 debug/run.asm   |  5 ---
 4 files changed, 108 insertions(+), 11 deletions(-)

diff --git a/debug/asm.asm b/debug/asm.asm
index b822346..bd8b8f7 100644
--- a/debug/asm.asm
+++ b/debug/asm.asm
@@ -1,9 +1,95 @@
 
-	; Prints instruction at ES:BX in human-readable form
-disasm:	call print_esbx
-	call space
-	mov si, instr.db
+	; Prints instruction at DS:SI in human-readable form
+disasm:	lodsb
+	mov bx, opcodes
+	jmp .scan
+
+.next:	add bx, 8
+.scan:	push ax
+	and al, [cs:bx]
+	cmp al, [cs:bx+1]
+	pop ax
+	jne .next
+
+	push si
+	push ax
+	mov si, [cs:bx+2]
 	call putcs
-	call crlf
+	pop ax
+	pop si
+
+	cmp word [cs:bx+4], 0
+	je .ret
+
+	push ax
+	call space
+	pop ax
+	push ax
+	call [cs:bx+4]
+	pop ax
+
+	cmp word [cs:bx+6], 0
+	je .ret
+
+	push ax
+	call print_sep
+	pop ax
+	jmp [cs:bx+6]
+.ret:	ret
+
+opcodes:
+	; word 1: H=opcode value after AND L
+	; word 2: ptr to memonic
+	; word 3: procedure to print first operand
+	; word 4: procedure to print second operand
+	dw 0x50F8, mnem.push, operand.inr16, 0
+	dw 0x58F8, mnem.pop, operand.inr16, 0
+	dw 0xB0F8, mnem.mov, operand.inr8, 0
+	dw 0xB8F8, mnem.mov, operand.inr16, operand.imm16
+	dw 0xA4FF, mnem.movsb, 0, 0
+	dw 0xA5FF, mnem.movsw, 0, 0
+	dw 0x0000, mnem.db, operand.self, 0
+
+print_sep:
+	mov al, ','
+	call putc
+	jmp space
+
+print_r8:
+	push di
+	mov di, bnames
+	call print_r
+	pop di
 	ret
 
+print_r16:
+	push di
+	mov di, rnames
+	call print_r
+	pop di
+	ret
+
+print_r:
+	push bx
+	mov bl, al
+	xor bh, bh
+	add bx, bx
+	mov bx, [cs:bx+di]
+	mov al, bl
+	call putc
+	mov al, bh
+	call putc
+	pop bx
+	ret
+
+operand:
+.inr8:	and al, 7
+	jmp print_r8
+.inr16:	and al, 7
+	jmp print_r16
+.self:	mov dl, al
+	jmp print_dl
+.imm8:	mov dl, [si]
+	jmp print_dl
+.imm16:	mov dx, [si]
+	jmp print_dx
diff --git a/debug/edit.asm b/debug/edit.asm
index 60d2114..17cf561 100644
--- a/debug/edit.asm
+++ b/debug/edit.asm
@@ -40,6 +40,15 @@ printregs:
 .fprnt: int 0x10
 .fskip: shl dx, 1
 	loop .floop
+
+	call space
+
+	push ds
+	mov ds, [es:reg_cs]
+	mov si, [es:reg_ip]
+	call disasm
+	pop ds
+
 	call crlf
 	ret
 
diff --git a/debug/names.asm b/debug/names.asm
index f9e0a88..06ca76e 100644
--- a/debug/names.asm
+++ b/debug/names.asm
@@ -4,10 +4,17 @@ rnames:	; general purpose regs
 	db "ESCSSSDS"
 	; special regs
 	db "IPFL"
+bnames:	; 8-bit registers
+	db "ALCLDLBLAHCHDHBH"
 fnames:	; control flags
 	db "++++ODIT"
 	; status flags
 	db "SZ+A+P+C"
 
-instr:
+mnem:
 .db:	db "DB", 0
+.push:	db "PUSH", 0
+.pop:	db "POP", 0
+.mov:	db "MOV", 0
+.movsb:	db "MOVSB", 0
+.movsw:	db "MOVSW", 0
diff --git a/debug/run.asm b/debug/run.asm
index 98bb634..d110254 100644
--- a/debug/run.asm
+++ b/debug/run.asm
@@ -40,11 +40,6 @@ 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, '-'