2020-03-07 12:13:15 -05:00
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; 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.
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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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ld (ix), l
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inc ix
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ld (ix), h
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inc ix
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ret
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; Pop RS' TOS to HL
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popRS:
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dec ix
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ld h, (ix)
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dec ix
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ld l, (ix)
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ret
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2020-03-07 20:20:11 -05:00
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; Verifies that SP is within bounds. If it's not, call ABORT
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chkPS:
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ld hl, (INITIAL_SP)
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; We have the return address for this very call on the stack. Let's
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; compensate
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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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ret nc ; (INITIAL_SP) >= SP? good
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; underflow
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ld hl, .msg
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call printstr
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2020-03-07 22:18:14 -05:00
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jp abort
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2020-03-07 20:20:11 -05:00
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.msg:
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.db "stack underflow", 0
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