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34ee91a0d7
This will soon allow use to seek and tell on input, which is necessary for a second pass which is necessary for forward symbol references. This require making `blkSel` a bit more flexible. Rather than having one global selected blkdev, each app can select its own, in its own memory space.
221 lines
4.8 KiB
NASM
221 lines
4.8 KiB
NASM
; blockdev
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;
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; A block device is an abstraction over something we can read from, write to.
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;
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; A device that fits this abstraction puts the properly hook into itself, and
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; then the glue code assigns a blockdev ID to that device. It then becomes easy
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; to access arbitrary devices in a convenient manner.
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;
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; This part exposes a new "bsel" command to select the currently active block
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; device.
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; *** DEFINES ***
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; BLOCKDEV_COUNT: The number of devices we manage.
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; *** CONSTS ***
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BLOCKDEV_ERR_OUT_OF_BOUNDS .equ 0x03
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BLOCKDEV_ERR_UNSUPPORTED .equ 0x04
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BLOCKDEV_SEEK_ABSOLUTE .equ 0
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BLOCKDEV_SEEK_FORWARD .equ 1
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BLOCKDEV_SEEK_BACKWARD .equ 2
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BLOCKDEV_SEEK_BEGINNING .equ 3
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BLOCKDEV_SEEK_END .equ 4
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; *** VARIABLES ***
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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_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 and place them in routine pointers at (DE).
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; For example, for a "regular" blkSel, you will want to set DE to BLOCKDEV_GETC.
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blkSel:
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push af
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push de
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push hl
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ld hl, blkDevTbl
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cp 0
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jr z, .afterloop ; index is zero? don't loop
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push bc
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ld b, a
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.loop:
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ld a, 8
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call addHL
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djnz .loop
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pop bc
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.afterloop:
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push hl
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call intoHL
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call writeHLinDE
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inc de
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inc de
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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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call writeHLinDE
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inc de
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inc de
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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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call writeHLinDE
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inc de
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inc de
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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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call writeHLinDE
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pop hl
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pop de
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pop af
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ret
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; call IX unless it's zero
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_blkCall:
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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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cp ixh
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jr nz, .ok ; not zero, ok
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cp ixl
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jr z, .error ; zero, error
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.ok:
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pop af
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call callIX
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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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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 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 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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ret
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; Reads B chars from blkGetC and copy them in (HL).
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; Sets Z if successful, unset Z if there was an error.
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blkRead:
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ld ix, (BLOCKDEV_GETC)
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_blkRead:
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push hl
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push bc
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.loop:
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call _blkCall
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jr nz, .end ; Z already unset
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ld (hl), a
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inc hl
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djnz .loop
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cp a ; ensure Z
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.end:
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pop bc
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pop hl
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ret
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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 ix, (BLOCKDEV_PUTC)
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jr _blkCall
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; Writes B chars to blkPutC from (HL).
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; Sets Z if successful, unset Z if there was an error.
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blkWrite:
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ld ix, (BLOCKDEV_PUTC)
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_blkWrite:
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push hl
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push bc
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.loop:
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ld a, (hl)
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call _blkCall
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jr nz, .end ; Z already unset
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inc hl
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djnz .loop
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cp a ; ensure Z
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.end:
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pop bc
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pop hl
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ret
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; Seeks the block device in one of 5 modes, which is the A argument:
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; 0 : Move exactly to X, X being the HL argument.
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; 1 : Move forward by X bytes, X being the HL argument
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; 2 : Move backwards by X bytes, X being the HL argument
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; 3 : Move to the end
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; 4 : Move to the beginning
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; Set position of selected device to the value specified in HL
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;
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; When seeking to an out-of-bounds position, the resulting position will be
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; one position ahead of the last valid position. Therefore, GetC after a seek
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; to end would always fail.
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;
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; If the device is "growable", it's possible that seeking to end when calling
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; PutC doesn't necessarily result in a failure.
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blkSeek:
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ld ix, (BLOCKDEV_SEEK)
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ld iy, (BLOCKDEV_TELL)
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_blkSeek:
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push de
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cp BLOCKDEV_SEEK_FORWARD
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jr z, .forward
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cp BLOCKDEV_SEEK_BACKWARD
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jr z, .backward
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cp BLOCKDEV_SEEK_BEGINNING
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jr z, .beginning
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cp BLOCKDEV_SEEK_END
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jr z, .end
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; all other modes are considered absolute
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jr .seek ; for absolute mode, HL is already correct
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.forward:
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ex hl, de ; DE has our offset
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; We want to be able to plug our own TELL function, which is why we
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; don't call blkTell directly here.
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; Calling TELL
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call callIY ; HL has our curpos
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add hl, de
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jr nc, .seek ; no carry? alright!
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; we have carry? out of bounds, set to maximum
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.backward:
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; TODO - subtraction are more complicated...
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jr .seek
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.beginning:
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ld hl, 0
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jr .seek
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.end:
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ld hl, 0xffff
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.seek:
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pop de
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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 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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; a list of device routine table entries just after the include. Each line
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; has 4 word addresses: GetC, PutC and Seek, Tell. An entry could look like:
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; .dw mmapGetC, mmapPutC, mmapSeek, mmapTell
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blkDevTbl:
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