collapseos/apps/forth/stack.asm

; The Parameter stack (PS) is maintained by SP and the Return stack (RS) is
; maintained by IX. This allows us to generally use push and pop freely because
; PS is the most frequently used. However, this causes a problem with routine
; calls: because in Forth, the stack isn't balanced within each call, our return
; offset, when placed by a CALL, messes everything up. This is one of the
; reasons why we need stack management routines below. IX always points to RS'
; Top Of Stack (TOS)
;
; This return stack contain "Interpreter pointers", that is a pointer to the
; address of a word, as seen in a compiled list of words.

; Push value HL to RS
pushRS:
	inc	ix
	inc	ix
	ld	(ix), l
	ld	(ix+1), h
	ret

; Pop RS' TOS to HL
popRS:
	ld	l, (ix)
	ld	h, (ix+1)
	dec ix
	dec ix
	ret

; Skip the next two bytes in RS' TOS
skipRS:
	push	hl
	ld	l, (ix)
	ld	h, (ix+1)
	inc	hl \ inc hl
	ld	(ix), l
	ld	(ix+1), h
	pop	hl
	ret

; Verifies that SP is within bounds. If it's not, call ABORT
chkPS:
	ld	hl, (INITIAL_SP)
	; We have the return address for this very call on the stack. Let's
	; compensate
	dec	hl \ dec hl
	or	a		; clear carry
	sbc	hl, sp
	ret	nc		; (INITIAL_SP) >= SP? good
	; underflow
	ld	hl, .msg
	call	printstr
	jp	abort
.msg:
	.db "stack underflow", 0
apps/forth: new (WIP) application 2020-03-07 12:13:15 -05:00			`; The Parameter stack (PS) is maintained by SP and the Return stack (RS) is`
			`; maintained by IX. This allows us to generally use push and pop freely because`
			`; PS is the most frequently used. However, this causes a problem with routine`
			`; calls: because in Forth, the stack isn't balanced within each call, our return`
			`; offset, when placed by a CALL, messes everything up. This is one of the`
forth: simplify execution model and handle literals better This scheme of "when we handle line-by-line, compile one word at a time then execute" so that we could allow words like "CREATE" to call "readword" before continuing was a bad scheme. It made things like branching outside of a colon definition impossible. This commit implement a new "litWord". When an undefined word is encountered at compile time, it is included as-is in a string literal word. It is at run time that we decide what to do with it. 2020-03-09 08:49:51 -04:00			`; reasons why we need stack management routines below. IX always points to RS'`
			`; Top Of Stack (TOS)`
apps/forth: new (WIP) application 2020-03-07 12:13:15 -05:00			`;`
			`; This return stack contain "Interpreter pointers", that is a pointer to the`
			`; address of a word, as seen in a compiled list of words.`

			`; Push value HL to RS`
			`pushRS:`
			`inc ix`
			`inc ix`
forth: simplify execution model and handle literals better This scheme of "when we handle line-by-line, compile one word at a time then execute" so that we could allow words like "CREATE" to call "readword" before continuing was a bad scheme. It made things like branching outside of a colon definition impossible. This commit implement a new "litWord". When an undefined word is encountered at compile time, it is included as-is in a string literal word. It is at run time that we decide what to do with it. 2020-03-09 08:49:51 -04:00			`ld (ix), l`
			`ld (ix+1), h`
apps/forth: new (WIP) application 2020-03-07 12:13:15 -05:00			`ret`

			`; Pop RS' TOS to HL`
			`popRS:`
forth: simplify execution model and handle literals better This scheme of "when we handle line-by-line, compile one word at a time then execute" so that we could allow words like "CREATE" to call "readword" before continuing was a bad scheme. It made things like branching outside of a colon definition impossible. This commit implement a new "litWord". When an undefined word is encountered at compile time, it is included as-is in a string literal word. It is at run time that we decide what to do with it. 2020-03-09 08:49:51 -04:00			`ld l, (ix)`
			`ld h, (ix+1)`
apps/forth: new (WIP) application 2020-03-07 12:13:15 -05:00			`dec ix`
			`dec ix`
			`ret`
forth: Check for PS underflow 2020-03-07 20:20:11 -05:00
forth: change the whole execution model again Things are better now, but immediates inside colons are broken. However, IF/THEN/ELSE are now immediates and it's much cleaner this way. Still, this commit has too much stuff in it, I need to commit, I don't want to lose this step. 2020-03-10 21:37:06 -04:00			`; Skip the next two bytes in RS' TOS`
			`skipRS:`
			`push hl`
			`ld l, (ix)`
			`ld h, (ix+1)`
			`inc hl \ inc hl`
			`ld (ix), l`
			`ld (ix+1), h`
			`pop hl`
			`ret`

forth: Check for PS underflow 2020-03-07 20:20:11 -05:00			`; Verifies that SP is within bounds. If it's not, call ABORT`
			`chkPS:`
			`ld hl, (INITIAL_SP)`
			`; We have the return address for this very call on the stack. Let's`
			`; compensate`
			`dec hl \ dec hl`
			`or a ; clear carry`
			`sbc hl, sp`
			`ret nc ; (INITIAL_SP) >= SP? good`
			`; underflow`
			`ld hl, .msg`
			`call printstr`
forth: add "DOES>" and "CONSTANT" 2020-03-07 22:18:14 -05:00			`jp abort`
forth: Check for PS underflow 2020-03-07 20:20:11 -05:00			`.msg:`
			`.db "stack underflow", 0`