67 lines
1.4 KiB
NASM
67 lines
1.4 KiB
NASM
; The Parameter stack (PS) is maintained by SP and the Return stack (RS) is
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; maintained by IX. This allows us to generally use push and pop freely because
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; PS is the most frequently used. However, this causes a problem with routine
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; calls: because in Forth, the stack isn't balanced within each call, our return
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; offset, when placed by a CALL, messes everything up. This is one of the
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; reasons why we need stack management routines below. IX always points to RS'
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; Top Of Stack (TOS)
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;
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; This return stack contain "Interpreter pointers", that is a pointer to the
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; address of a word, as seen in a compiled list of words.
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; Push value HL to RS
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pushRS:
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inc ix
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inc ix
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ld (ix), l
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ld (ix+1), h
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ret
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; Pop RS' TOS to HL
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popRS:
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ld l, (ix)
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ld h, (ix+1)
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dec ix
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dec ix
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ret
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popRSIP:
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call popRS
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ld (IP), hl
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ret
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; Skip the next two bytes in RS' TOS
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skipRS:
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push hl
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ld l, (ix)
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ld h, (ix+1)
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inc hl \ inc hl
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ld (ix), l
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ld (ix+1), h
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pop hl
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ret
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; Verifies that SP and RS are within bounds. If it's not, call ABORT
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chkRS:
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push ix \ pop hl
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push de ; --> lvl 1
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ld de, RS_ADDR
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or a ; clear carry
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sbc hl, de
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pop de ; <-- lvl 1
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jp c, abortUnderflow
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ret
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chkPS:
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push hl
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ld hl, (INITIAL_SP)
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; We have the return address for this very call on the stack and
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; protected registers. Let's compensate
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dec hl \ dec hl
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dec hl \ dec hl
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or a ; clear carry
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sbc hl, sp
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pop hl
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ret nc ; (INITIAL_SP) >= SP? good
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jp abortUnderflow
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