;P.C. Debug Monitor  Revision 6/23/2005  by Don Stoner
;
	ORG 100H	;DOS file.COM execution begins here
;
;==========================================================
;
; Code Begins Here:
;
	JMP SHORT START
;
;------------------------------------------------
;
; USER REGISTER CONTENTS:
;
RAX:	DW 1111H
RBX:	DW 8000H
RCX:	DW 3333H
RDX:	DW 4444H
RSI:	DW 5555H
RDI:	DW 6666H
RBP:	DW 7777H
RSP:	DW 0FF80H
RCS:	DW 0
RDS:	DW 0
RES:	DW 0
RSS:	DW 0
RIP:	DW 100H
RFG:	DW 0
;
;==========================================================
;
; SETUP
;
; TAKE OVER INTERRUPT VECTORS 1 (STEP) AND 3 (BREAK)
;
START:	MOV AX,0
	MOV DS,AX
	;
	MOV AX,[4]	;SAVE EXISTING VECTORS
	MOV [CS:OFFSAV],AX
	MOV AX,[6]
	MOV [CS:SEGSAV],AX
	;
	MOV AX,VECTOR	;SET NEW VECTORS
	MOV [4],AX
	MOV [12],AX
	MOV AX,CS
	MOV [6],AX
	MOV [14],AX
;
;  Set up segment registers:
;
	MOV AX,CS
	MOV [RCS],AX
	MOV [RDS],AX
	MOV [RES],AX
	MOV [RSS],AX
RESTART:
	MOV AX,CS
	MOV DS,AX
	MOV ES,AX
	CLI		;NO INTERRUPTS
	MOV SS,AX	;WHILE SETTING
	MOV SP,0FFFEH	;STACK POINTER
	STI
;
;================================================
;
; Main Code Loop
;
MLOOP:	CALL CRLF	;Clear Screen
	CALL BLKOUT
	CALL INPUT	;GET INPUT
	MOV [KEY],AX
	;
	;----------------------------------------
	;
	; Quit to DOS (only for debug under DOS)
	;
	CMP AL,"Q"	;KEY IS Q?
	JNZ NTQ
	;
	MOV AX,0	;RESTORE INTERRUPT VECTORS
	MOV DS,AX
	MOV AX,[CS:OFFSAV]
	MOV [4],AX
	MOV [12],AX
	MOV AX,[CS:SEGSAV]
	MOV [6],AX
	MOV [14],AX
	;
	MOV AH,0	;"EXIT DOS" FUNCTION CALL
	INT 21H
NTQ:	;
	;========================================
	;
	; GO (RUN)
	;
	CMP AL,"G"	;KEY IS G?
	JNZ NTG
	JMP RUN
NTG:	;
	;----------------------------------------
	;
	; SINGLE STEP
	;
	CMP AL,"S"	;KEY IS S?
	JNZ NTS
	JMP STEP
NTS:	;
	JMP MLOOP
;
;==========================================================
;
; SUBROUTINES:
;
	;----------------------------------------
	;
	; INPUT ASCII KEY CODE INTO AL
	; (EXTENDED KEY CODE INTO AX)
	; uses BIOS interrupt
	;
	INPUT:	MOV AH,0
		INT 16H
		RET
	;
	;----------------------------------------
	;
	; HEX OUTPUT (FROM AX OR AL)
	;
	AXOUT:	;PUSH AX		;4 NIBBLES FROM AX
		;MOV AL,AH
		xchg al,ah
		CALL ALOUT
		xchg ah,al
		;POP AX
	;
	ALOUT:	PUSH AX		;2 NIBBLES FROM AQL
		PUSH CX
		MOV CL,4
		ROR AL,CL
		POP CX
		CALL LSNOUT
		POP AX
	;
	LSNOUT:	AND AL,0FH	;LSN ONLY
		OR AL,30H
		CMP AL,3AH	;HEX ALPHA
		JC OUTPUT
		ADD AL,41H-3AH	;*** drops through ***
	;
	; OUTPUT ASCII CHARACTER (FROM AL)
	; (uses BIOS interrupt)
	;
	OUTPUT:	PUSH AX		;SAVE AX
		MOV AH,0EH	;TTY OUT
		MOV BX,0	;FOREGROUND PAGE,COLOR
		INT 10H
		POP AX		;RESTORE AX
		RET
	;
	;----------------------------------------
	;
	; SPACE OUTPUT
	;
	SPACE:	PUSH AX
		MOV AL," "
		CALL OUTPUT
		POP AX
		RET
	;
	;----------------------------------------
	;
	; C.R. AND L.F.
	;
	CRLF:	MOV AL,0DH
		CALL OUTPUT
	LF:	MOV AL,0AH
		JMP SHORT OUTPUT
	;
	;----------------------------------------
	;
	;  OUTPUT AN ASCIIZ CHARACTER STRING (POINTED BY SI)
	;
	PRINTS:	LODSB	;(LODS - SAME AS MOV AL,[SI] INC SI)
		AND AL,AL	;END/NULL STRING?
		JZ ENDSTR
		CALL OUTPUT	;OUTPUT IT
		JMP SHORT PRINTS
	ENDSTR:	RET
	;
	;----------------------------------------
	;
	; BLOCK OUTPUT
	;
	BLKOUT:	MOV SI,MAX	;AX OUT
		CALL PRINTS
		MOV AX,[RAX]
		CALL AXOUT
		;
		MOV SI,MBX	;BX OUT
		CALL PRINTS
		MOV AX,[RBX]
		CALL AXOUT
		;
		MOV SI,MCX	;CX OUT
		CALL PRINTS
		MOV AX,[RCX]
		CALL AXOUT
		;
		MOV SI,MDX	;DX OUT
		CALL PRINTS
		MOV AX,[RDX]
		CALL AXOUT
		;
		MOV SI,MSI	;SI OUT
		CALL PRINTS
		MOV AX,[RSI]
		CALL AXOUT
		;
		MOV SI,MDI	;DI OUT
		CALL PRINTS
		MOV AX,[RDI]
		CALL AXOUT
		;
		MOV SI,MBP	;BP OUT
		CALL PRINTS
		MOV AX,[RBP]
		CALL AXOUT
		;
		MOV SI,MSP	;SP OUT
		CALL PRINTS
		MOV AX,[RSP]
		CALL AXOUT
		;
		MOV SI,MCS	;CS OUT
		CALL PRINTS
		MOV AX,[RCS]
		CALL AXOUT
		;
		MOV SI,MDS	;DS OUT
		CALL PRINTS
		MOV AX,[RDS]
		CALL AXOUT
		;
		MOV SI,MES	;ES OUT
		CALL PRINTS
		MOV AX,[RES]
		CALL AXOUT
		;
		MOV SI,MSS	;SS OUT
		CALL PRINTS
		MOV AX,[RSS]
		CALL AXOUT
		;
		MOV SI,MIP	;IP OUT
		CALL PRINTS
		MOV AX,[RIP]
		MOV DI,AX
		CALL AXOUT
		;
		MOV SI,MFG	;FLAGS OUT
		CALL PRINTS
		MOV AX,[RFG]
		CALL AXOUT
		;
		MOV SI,MEND
		CALL PRINTS
		JMP CRLF
;
;==========================================================
;
; SINGLE STEP OR RUN (INSIDE OUT INTERRUPT)
;
STEP:	MOV AX,[RFG]
	OR AX,100H	;SINGLE STEP FLAG BIT ON
	MOV [RFG],AX
	;
RUN:	MOV AX,[RSS]	;"RESTORE" USER STACK
	CLI
	MOV SS,AX
	MOV SP,[RSP]
	STI
	;
	;PUSH [RFG]
	DW 36FFH,RFG	;SETUP IRET STUFF
	;PUSH [RCS]	;(ON USER'S STACK)
	DW 36FFH,RCS
	;PUSH [RIP]
	DW 36FFH,RIP	;(ASSEMBLER WORKAROUND)
	;
	MOV AX,[RES]	;"RESTORE" ALL REGISTERS
	MOV ES,AX
	MOV BP,[RBP]
	MOV DI,[RDI]
	MOV SI,[RSI]
	MOV DX,[RDX]
	MOV CX,[RCX]
	MOV BX,[RBX]
	;
	;PUSH [RAX]
	DW 36FFH,RAX	;THESE ARE TRICKY
	MOV AX,[RDS]	;BECAUSE WE LOSE THE
	MOV DS,AX	;D-SEGMENT REGISTER
	POP AX
	;
	IRET		;GO DO IT USING A INTERRUPT RETURN
;----------------------------------------------------------
;			;THEN "RETURN" USING AN INTERRUPT
;
; INTERRUPT 1 (STEP) OR 3 (BREAK) RETURNS
;  (FLAGS,CS,IP ARE ON STACK)
;
VECTOR:	PUSH DS		;SAVE THESE (ON THE USER STACK)
	PUSH AX		;BECAUSE WE NEED THE REGISTERS
	MOV AX,CS
	MOV DS,AX	;TO GET ACCESS TO MEMORY
	;
	POP AX
	MOV [RAX],AX	;RECOVER AX
	MOV [RBX],BX
	MOV [RCX],CX	;SAVE ALL REGISTERS
	MOV [RDX],DX
	MOV [RSI],SI
	MOV [RDI],DI
	MOV [RBP],BP
	; 
	;POP [RDS]	;SEGMENT REGISTERS
	;DWL 368FH,RDS	;(WORKAROUND)
	POP AX
	MOV [RDS],AX
	MOV AX,ES
	MOV [RES],AX
	;
	;POP [RIP]	;RECOVER IRET STUFF FROM STACK
	;DWL 368FH,RIP	;(WORKAROUND)
	POP AX
	MOV [RIP],AX
	;POP [RCS]
	;DWL 368FH,RCS
	POP AX
	MOV [RCS],AX
	;POP [RFG]
	;DWL 368FH,RFG
	POP AX
	MOV [RFG],AX
	;
	MOV AX,SS	;RECOVER USER STACK POINTERS
	MOV [RSS],AX
	MOV [RSP],SP
	;
	MOV AX,[RFG]
	AND AX,0FEFFH	;SINGLE STEP FLAG BIT OFF
	MOV [RFG],AX
	;
	JMP RESTART	;RESTART PROGRAM LOOP
	;
;==========================================================
;
; MONITOR VARIABLES
;
SEGSAV:	DW 0
OFFSAV:	DW 0		;SEG:OFF OF OLD INTERRUPT VECTORS
KEY:	DW 20H		;IMAGE OF LAST TYPED KEY
;
; Messages:
;
MAX:	DB 13,10,"AX:",0
MBX:	DB " BX:",0
MCX:	DB " CX:",0
MDX:	DB " DX:",0
MSI:	DB " SI:",0
MDI:	DB " DI:",0
MBP:	DB " BP:",0
MSP:	DB " SP:",0
MCS:	DB 13,10,"CS:",0
MDS:	DB " DS:",0
MES:	DB " ES:",0
MSS:	DB " SS:",0
MIP:	DB " IP:",0
MFG:	DB " FLAGS:",0
MINST:	DB " INST:",0
MKEY:	DB "  KEY: ",0
MFPU:	DB 13,10,"FPU:",0
MEND:	DB 13,10,10,0