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blockdev: remove a layer of indirection in block routine storage
This will facilitate "copying" blk selection in FS.
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@ -26,8 +26,11 @@ BLOCKDEV_SEEK_END .equ 4
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; Pointer to the selected block device. A block device is a 8 bytes block of
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; memory with pointers to GetC, PutC, Seek and Tell routines, in that order.
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; 0 means unsupported.
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BLOCKDEV_SEL .equ BLOCKDEV_RAMSTART
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BLOCKDEV_RAMEND .equ BLOCKDEV_SEL+2
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BLOCKDEV_GETC .equ BLOCKDEV_RAMSTART
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BLOCKDEV_PUTC .equ BLOCKDEV_GETC+2
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BLOCKDEV_SEEK .equ BLOCKDEV_PUTC+2
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BLOCKDEV_TELL .equ BLOCKDEV_SEEK+2
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BLOCKDEV_RAMEND .equ BLOCKDEV_TELL+2
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; *** CODE ***
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; Select block index specified in A
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@ -45,36 +48,32 @@ blkSel:
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djnz .loop
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pop bc
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.afterloop:
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ld (BLOCKDEV_SEL), hl
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push hl
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call intoHL
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ld (BLOCKDEV_GETC), hl
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pop hl
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inc hl
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inc hl
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push hl
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call intoHL
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ld (BLOCKDEV_PUTC), hl
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pop hl
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inc hl
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inc hl
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push hl
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call intoHL
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ld (BLOCKDEV_SEEK), hl
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pop hl
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inc hl
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inc hl
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call intoHL
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ld (BLOCKDEV_TELL), hl
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pop hl
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pop af
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ret
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; In those routines below, IY is destroyed (we don't push it to the stack). We
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; seldom use it anyways...
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; set IX to the address of the routine in BLOCKDEV_SEL with offset IYL.
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_blkCallAddr:
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push de
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ld de, (BLOCKDEV_SEL)
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; DE now points to the *address table*, not the routine addresses
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; themselves. One layer of indirection left.
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; slide by offset
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push af
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ld a, iyl
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call addDE ; slide by offset
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pop af
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call intoDE
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; Alright, now de points to what we want to call
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ld ixh, d
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ld ixl, e
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pop de
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ret
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; call routine in BLOCKDEV_SEL with offset IYL.
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; call IX unless it's zero
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_blkCall:
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push ix
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call _blkCallAddr
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; Before we call... is IX zero? We don't want to call a zero.
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push af
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xor a
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@ -85,25 +84,22 @@ _blkCall:
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.ok:
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pop af
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call callIX
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jr .end
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ret
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.error:
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pop af
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ld a, BLOCKDEV_ERR_UNSUPPORTED
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.end:
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pop ix
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ret
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; Reads one character from selected device and returns its value in A.
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; Sets Z according to whether read was successful: Set if successful, unset
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; if not.
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blkGetC:
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ld iyl, 0
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ld ix, (BLOCKDEV_GETC)
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jr _blkCall
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; Repeatedly call blkGetC until the call is a success.
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blkGetCW:
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ld iyl, 0
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call _blkCallAddr
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ld ix, (BLOCKDEV_GETC)
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.loop:
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call callIX
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jr nz, .loop
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@ -127,7 +123,7 @@ blkRead:
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; Writes character in A in current position in the selected device. Sets Z
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; according to whether the operation was successful.
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blkPutC:
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ld iyl, 2
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ld ix, (BLOCKDEV_PUTC)
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jr _blkCall
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; Writes B chars to blkPutC from (HL).
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@ -180,12 +176,12 @@ blkSeek:
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ld hl, 0xffff
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.seek:
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pop de
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ld iyl, 4
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ld ix, (BLOCKDEV_SEEK)
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jr _blkCall
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; Returns the current position of the selected device in HL.
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blkTell:
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ld iyl, 6
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ld ix, (BLOCKDEV_TELL)
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jr _blkCall
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; This label is at the end of the file on purpose: the glue file should include
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