2019-04-15 16:53:11 -04:00
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; 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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2019-04-15 20:38:25 -04:00
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BLOCKDEV_ERR_OUT_OF_BOUNDS .equ 0x03
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2019-04-15 16:53:11 -04:00
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; *** VARIABLES ***
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; A memory pointer to a device table. A device table is a list of addresses
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; pointing to GetC and PutC routines.
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BLOCKDEV_TBL .equ BLOCKDEV_RAMSTART
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; Index of the current blockdev selection
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BLOCKDEV_SELIDX .equ BLOCKDEV_TBL+(BLOCKDEV_COUNT*4)
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; Address of the current GetC routine
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BLOCKDEV_GETC .equ BLOCKDEV_SELIDX+1
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; Address of the current PutC routine
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BLOCKDEV_PUTC .equ BLOCKDEV_GETC+2
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BLOCKDEV_RAMEND .equ BLOCKDEV_PUTC+2
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; *** CODE ***
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; set DE to point to the table entry at index A.
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blkFind:
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ld de, BLOCKDEV_TBL
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cp 0
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ret z ; index is zero? don't loop
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push bc
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ld b, a
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push af
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ld a, 4
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.loop:
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call addDE
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djnz .loop
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pop af
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pop bc
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ret
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; Set the GetC pointer of device id A to the value in HL
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blkSetGetC:
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call blkFind
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call writeHLinDE
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ret
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; Set the GetC pointer of device id A to the value in HL
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blkSetPutC:
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call blkFind
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inc de
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inc de
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call writeHLinDE
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ret
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; Select block index specified in A
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blkSel:
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call blkFind
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ld (BLOCKDEV_SELIDX), a
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ex hl, de
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; now, HL points to the table entry
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ld de, BLOCKDEV_GETC
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ldi ; copy (HL) into (BLOCKDEV_GETC)
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ldi ; .. and into +1
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ld de, BLOCKDEV_PUTC
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ldi ; same thing for (BLOCKDEV_PUTC)
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ldi
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ret
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blkBselCmd:
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.db "bsel", 0b001, 0, 0
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blkBsel:
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ld a, (hl) ; argument supplied
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cp BLOCKDEV_COUNT
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2019-04-15 20:38:25 -04:00
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jr nc, .error ; if selection >= device count, error
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2019-04-15 16:53:11 -04:00
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call blkSel
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2019-04-15 20:38:25 -04:00
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xor a
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ret
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.error:
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ld a, BLOCKDEV_ERR_OUT_OF_BOUNDS
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2019-04-15 16:53:11 -04:00
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ret
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; Reads one character from blockdev ID specified at A and returns its value
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; in A. Always returns a character and waits until read if it has to.
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blkGetC:
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push ix
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push de
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ld de, (BLOCKDEV_GETC)
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ld ixh, d
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ld ixl, e
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pop de
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call callIX
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pop ix
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ret
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blkPutC:
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push ix
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push de
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ld de, (BLOCKDEV_PUTC)
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ld ixh, d
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ld ixl, e
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pop de
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call callIX
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pop ix
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ret
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