* H316 SAFE SOFTWARE STACK, REV. 0.1
*
*
* AUTHOR: 
* 
*       PHILIPP HACHTMANN, 2007
* 
* VERSIONS:
* 
*               0.1 - INITIAL REVISION (22.12.2007)
* 
* PURPOSE:
* 
*       TO PROVIDE A MULTI-PURPOSE STACK MECHANISM
*       TO PROVIDE A SPECIAL-PURPOSE STACK MECHANISM FOR RECURSIVE
*       PROGRAM CALLS
*
* WHAT:
* 
* THIS VARIANT OF THE STACK ROUTINE USES A FIXED SIZE MEMORY 
* BUFFER FOR THE THE STACK. THE STACK USAGE IS MONITORED.
* ON OVERFLOW, THE COMPUTER TYPES OUT AN ERROR MESSAGE AND HALTS.
* 
* 
* USAGE:
* 
* INITIALISING STACK POINTER:
*       
*       CALL S$INIT
* 
* PUSHING AND POPPING THE A-REGISTER FROM AND TO THE STACK:
* 
*       CALL    S$PUSH  VALUE IN A REGISTER IS PUSHED.
*       CALL    $$PUSH  VALUE FROM STACK IS POPPED INTO A-REGISTER.
* 
* PUSHING AND POPPING ARBITRARY DATA FROM AND TO THE STACK:
* 
*       CALL    S$PUSM
*       DAC     ADDRESS
*       OCT     SIZE
*  
*       CALL    S$POPM
*       DAC     ADDRESS
*       OCT     SIZE
* 
* 
********************************************************************************
*
* 
**** SYMBOL DECLARATIONS
* 
	SUBR	STACK,SBUF	JUST A LABEL FOR THE OBJECT TAPE
	SUBR	S$INIT,INIT	INITITALISATION
	SUBR	S$PUSH,PUSH	SINGLE WORD PUSH
	SUBR	S$POP,POP	SINGLE WORD POP
	SUBR	S$PUSM,PUSM	MEMORY RANGE PUSH
	SUBR	S$POPM,POPM	MEMORY RANGE POP
	SUBR	S$PTR,SPTR	STACK POINTER ACCESS
* 
* 	
********************************************************************************
* 
*  
SSIZ	EQU	'1000	512 WORDS DEFAULT STACK BUFFER SIZE
* 
	REL		RELOCATEABLE OBJECT
	ORG	'0
*  
* 
********************************************************************************
* 
* 
**** PUSH MEMORY RANGE TO STACK
* 
PUSM	DAC	**	ENTRY POINT TO PUSH ROUTINE
	STA	ATM1	SAVE A-REGISTER
* 
	LDA*	PUSM	LOAD POINTER
	STA	PTR	STORE TO TRANSFER POINTER
	IRS	PUSM	GO TO NEXT ARGUMENT
	LDA*	PUSM	LOAD TRANSFER SIZE
	IRS	PUSM	CORRECT RETURN ADDRESS
* 
	TCA		NEGATE WORD COUNT
	STA	CNT	STORE TO COUNTER
* 
PULP	LDA*	PTR	GET DATA
	JST	PUSH	PUSH IT!
	IRS	PTR	INCREMENT POINTER
	IRS	CNT	INCREMENT BYTE COUNTER
	JMP	PULP	DO IT AGAIN!
* 
	LDA	ATM1	RESTORE A-REG
	JMP*	PUSM	
* 
*
********************************************************************************
*
* 
**** POP MEMORY RANGE FROM STACK
* 
POPM	DAC	**	ENTRY POINT TO PUSH ROUTINE
	STA	ATM1	SAVE A-REGISTER
* 
	LDA*	POPM	LOAD POINTER
	IRS	POPM	GO TO NEXT ARGUMENT
	ADD*	POPM	ADD TRANSFER SIZE
	SUB	=1	SUBSTRACT 1 TO GET HIGH ADDRESS
	STA	PTR	STORE TO TRANSFER POINTER
	LDA*	POPM	LOAD TRANSFER SIZE
	IRS	POPM	CORRECT RETURN ADDRESS
* 
	TCA		NEGATE WORD COUNT
	STA	CNT	STORE TO COUNTER
* 
POLP	JST	POP	POP DATA FROM THE STACK
	STA*	PTR	STORE IT.
	LDA	PTR
	SUB	=1	DECREMENT
	STA	PTR	WRITE BACK
	IRS	CNT	INCREMENT BYTE COUNTER
	JMP	POLP	DO IT AGAIN!
* 
	LDA	ATM1
	JMP*	POPM	
* 
*
********************************************************************************
*
* 
**** PUSH SINGLE WORD ONTO STACK
* 
PUSH	DAC	**	REAL PUSH ROUTINE - PUSH AC TO STACK.
* 	
	STA	ATM2	SAVE A REGISTER
* 
	LDA	SPTR	LOAD STACK POINTER
	SUB	MAX	TEST IF STACK FULL
	SNZ
	JST	OFLO	OVERFLOW OH! OH! OH!
* 
	LDA	ATM2
	STA*	SPTR	NO OVERFLOW, PUT DATA ONTO STACK
	IRS	SPTR	INCREMENT STACK POINTER
* 
	JMP*	PUSH	RETURN WITH A-REG UNALTERED.
* 
* 
********************************************************************************
* 
* 
**** POP SINGLE WORD FROM STACK
* 
POP	DAC	**	REAL POP ROUTINE - POP AC FROM STACK.
* 
	LDA	SPTR	LOAD STACK POINTER
	SUB	MIN	TEST IF STACK EMPTY
	SNZ
	JST	UFLO	UNDERFLOW OH! OH! OH!
* 
	LDA	SPTR	LOAD STACK POINTER
	SUB	=1	DECREMENT IT TO LAST USED LOCATION
	STA	SPTR	SAVE IT BACK
* 
	LDA*	SPTR	LOAD VALUE FROM THE STACK
	JMP*	POP	RETURN.
* 
* 
******************************************************************************** 
*
* 
**** INITIALIZATION
* 
INIT	DAC	**	INITIALIZE STACK POINTER
	LDA	CPTR	LOAD INITIAL STACK POINTER
	STA	SPTR	SET STACK POINTER
	JMP*	INIT
* 
*
********************************************************************************
* 
*  
**** ERROR HANDLING ROUTINES
* 
OFLO	DAC	**	STACK OVERFLOW ROUTINE
	LDA	OMSP	LOAD OVERFLOW MESSAGE POINTER
	JST	TYPE	TYPE IT OUT.
* 
	HLT		WHAT WE DO: HALT THE MACHINE.
	JMP	*-1	YOU CANNOT SIMPLY LEAVE THIS, IT'S SERIOUS!
* 
* 
****************************************
* 
* 
UFLO	DAC	**	STACK OVERFLOW ROUTINE
	LDA	UMSP	LOAD OVERFLOW MESSAGE POINTER
	JST	TYPE	TYPE IT OUT.
* 
	HLT		WHAT WE DO: HALT THE MACHINE.
	JMP	*-1	YOU CANNOT SIMPLY LEAVE THIS, IT'S SERIOUS!
* 
* 
****************************************
* 
* 
TYPE	DAC	**
	SKS	'104	TEST ASR READY
	JMP	*-1	WAIT TO BECOME READY
	OCP	'104	SET TO OUTPUT MODE
* 
	STA	PTR	STORE POINTER
* 
TLOP	LDA*	PTR	TYPE LOOP
	SNZ		TEST FOR END
	JMP*	TYPE	RETURN
	ICA	
	OTA	'4
	JMP	*-1
	ICA
	OTA	'4
	JMP	*-1
	SKS	'104	ADDITIONAL TEST FOR READY
	JMP	*-1
	IRS	PTR	NEXT WORD.
	JMP	TLOP
* 
* 
********************************************************************************
*
* 
***** VARIABLES
* 
SBUF	BSS	SSIZ	THE STACK BUFFER
SPTR	DAC	SBUF	THE STACK POINTER
* 
PTR	DEC	0	TRANSFER POINTER TO USER BUFFERS
CNT	DEC	0	TRANSFER COUNTER
* 
ATM1	DEC	0	A-REGISTER BACKUP
ATM2	DEC	0	A-REGISTER BACKUP
* 
* 
***** CONSTANTS
* 
CPTR	DAC	SBUF	STACK POINTER CONSTANT
MAX	DAC	SBUF+SSIZ	FIRST ILLEGAL SPTR LOC BEFORE PUSH	
MIN	DAC	SBUF		FIRST ILLEGAL SPTR LOC BEFORE POP  
*
OMSP	DAC	OMSG		POINTER TO MESSAGE
UMSP	DAC	UMSG		POINTER TO MESSAGE
OMSG	OCT	'006412		CR/LF CHARACTERS
	BCI	16,STACK OVERFLOW, YOUR'RE SCREWED!
	DEC	0		TERMINATION CHARACTER
UMSG	OCT	'006412		CR/LF CHARACTERS
	BCI	17,STACK UNDERFLOW, YOUR'RE SCREWED!
	DEC	0		TERMINATION CHARACTER
*       
* 
********************************************************************************
*
* 
	END			THAT'S IT.