168 lines
4.4 KiB
NASM
168 lines
4.4 KiB
NASM
; I/Os in zasm
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;
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; As a general rule, I/O in zasm is pretty straightfoward. We receive, as a
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; parameter, two blockdevs: One that we can read and seek and one that we can
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; write to (we never seek into it).
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;
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; zasm doesn't buffers its reads during tokenization, which simplifies its
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; process. However, it also means that it needs, in certain cases, a "putback"
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; mechanism, that is, a way to say "you see that character I've just read? that
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; was out of my bounds. Could you make it as if I had never read it?". That
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; buffer is one character big and is made with the expectation that ioPutBack
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; is always called right after a ioGetC (when it's called).
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;
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; ioPutBack will mess up seek and tell offsets, so thath "put back" should be
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; consumed before having to seek and tell.
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;
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; That's for the general rules.
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;
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; Now, let's enter includes. To simplify processing, we make include mostly
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; transparent to all other units. They always read from ioGetC and a include
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; directive should have the exact same effect as copy/pasting the contents of
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; the included file in the caller.
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;
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; By the way: we don't support multiple level of inclusion. Only top level files
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; can include.
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;
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; When we include, all we do here is open the file with fsOpen and set a flag
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; indicating that we're inside an include. When that flag is on, GetC, Seek and
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; Tell are transparently redirected to their fs* counterpart.
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;
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; When we reach EOF in an included file, we transparently unset the "in include"
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; flag and continue on the general IN stream.
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; *** Variables ***
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.equ IO_IN_GETC IO_RAMSTART
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.equ IO_IN_PUTC IO_IN_GETC+2
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.equ IO_IN_SEEK IO_IN_PUTC+2
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.equ IO_IN_TELL IO_IN_SEEK+2
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.equ IO_OUT_GETC IO_IN_TELL+2
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.equ IO_OUT_PUTC IO_OUT_GETC+2
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.equ IO_OUT_SEEK IO_OUT_PUTC+2
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.equ IO_OUT_TELL IO_OUT_SEEK+2
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; Save pos for ioSavePos and ioRecallPos
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.equ IO_SAVED_POS IO_OUT_TELL+2
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; File handle for included source
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.equ IO_INCLUDE_HDL IO_SAVED_POS+2
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; see ioPutBack below
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.equ IO_PUTBACK_BUF IO_INCLUDE_HDL+FS_HANDLE_SIZE
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.equ IO_IN_INCLUDE IO_PUTBACK_BUF+1
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.equ IO_RAMEND IO_IN_INCLUDE+1
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; *** Code ***
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ioInit:
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xor a
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ld (IO_PUTBACK_BUF), a
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ld (IO_IN_INCLUDE), a
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ret
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ioGetC:
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ld a, (IO_PUTBACK_BUF)
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or a ; cp 0
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jr nz, .getback
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call ioInInclude
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jr z, .normalmode
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; We're in "include mode", read from FS
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push de
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ld de, IO_INCLUDE_HDL
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call fsGetC
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pop de
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or a ; cp 0
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ret nz ; not zero, all good
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; We reached EOF. What we do depends on whether we're in Local Pass
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; mode. Yes, I know, a bit hackish. Normally, we *should* be
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; transparently getting of include mode and avoid meddling with global
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; states, but here, we need to tell main.asm that the local scope if
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; over *before* we get off include mode, otherwise, our IO_SAVED_POS
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; will be wrong (an include IO_SAVED_POS used in global IN stream).
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call zasmIsLocalPass
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ld a, 0 ; doesn't affect Z flag
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ret z ; local pass? return EOF
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; regular pass (first or second)? transparently get off include mode.
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ld (IO_IN_INCLUDE), a ; A already 0
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; continue on to "normal" reading. We don't want to return our zero
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.normalmode:
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; normal mode, read from IN stream
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ld ix, (IO_IN_GETC)
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jp (ix)
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.getback:
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push af
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xor a
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ld (IO_PUTBACK_BUF), a
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pop af
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ret
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; Put back non-zero character A into the "ioGetC stack". The next ioGetC call,
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; instead of reading from IO_IN_GETC, will return that character. That's the
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; easiest way I found to handle the readWord/gotoNextLine problem.
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ioPutBack:
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ld (IO_PUTBACK_BUF), a
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ret
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ioPutC:
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ld ix, (IO_OUT_PUTC)
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jp (ix)
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ioSavePos:
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call _ioTell
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ld (IO_SAVED_POS), hl
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ret
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ioRecallPos:
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ld hl, (IO_SAVED_POS)
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jr _ioSeek
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ioRewind:
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ld hl, 0
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jr _ioSeek
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; always in absolute mode (A = 0)
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_ioSeek:
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call ioInInclude
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ld a, 0 ; don't alter flags
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jr nz, .include
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; normal mode, seek in IN stream
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ld ix, (IO_IN_SEEK)
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jp (ix)
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.include:
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; We're in "include mode", seek in FS
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push de
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ld de, IO_INCLUDE_HDL
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call fsSeek
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pop de
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ret
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_ioTell:
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call ioInInclude
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jp nz, .include
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; normal mode, seek in IN stream
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ld ix, (IO_IN_TELL)
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jp (ix)
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.include:
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; We're in "include mode", tell from FS
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push de
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ld de, IO_INCLUDE_HDL
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call fsTell
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pop de
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ret
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; Sets Z according to whether we're inside an include
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ioInInclude:
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ld a, (IO_IN_INCLUDE)
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or a ; cp 0
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ret
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; Open include file name specified in (HL).
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; Sets Z on success, unset on error.
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ioOpenInclude:
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call fsFindFN
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ret nz
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ld hl, IO_INCLUDE_HDL
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call fsOpen
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ld a, 1
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ld (IO_IN_INCLUDE), a
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cp a ; ensure Z
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ret
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