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blockdev: add Tell and fix blkGetCW

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Calling on blkGetC repeatedly was somehow very unstable and often
failed. I didn't pinpoint exactly why, but keeping the call addr around
and calling that instead seems like a better idea anyway.
This commit is contained in:
Virgil Dupras 2019-04-22 17:15:59 -04:00
parent 196d22c4ab
commit 1bcceb949c
2 changed files with 52 additions and 19 deletions
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61
parts/blockdev.asm
View File

@ -17,9 +17,9 @@ BLOCKDEV_ERR_OUT_OF_BOUNDS .equ 0x03
BLOCKDEV_ERR_UNSUPPORTED .equ 0x04
; *** VARIABLES ***
; Pointer to the selected block device. A block device is a 6 bytes block of
; memory with pointers to GetC, PutC and Seek routines, in that order. 0 means
; unsupported.
; Pointer to the selected block device. A block device is a 8 bytes block of
; memory with pointers to GetC, PutC, Seek and Tell routines, in that order.
; 0 means unsupported.
BLOCKDEV_SEL .equ BLOCKDEV_RAMSTART
BLOCKDEV_RAMEND .equ BLOCKDEV_SEL+2
@ -34,13 +34,13 @@ blkSel:
push bc
ld b, a
.loop:
ld a, 6
ld a, 8
call addHL
djnz .loop
pop bc
.afterloop:
ld (BLOCKDEV_SEL), hl
pop Hl
pop hl
pop af
ret
@ -60,9 +60,8 @@ blkBselCmd:
; In those routines below, IY is destroyed (we don't push it to the stack). We
; seldom use it anyways...
; call routine in BLOCKDEV_SEL with offset IYL.
_blkCall:
push ix
; set IX to the address of the routine in BLOCKDEV_SEL with offset IYL.
_blkCallAddr:
push de
ld de, (BLOCKDEV_SEL)
; DE now points to the *address table*, not the routine addresses
@ -77,19 +76,23 @@ _blkCall:
ld ixh, d
ld ixl, e
pop de
; Before we call... is it zero? We don't want to call a zero.
ret
; call routine in BLOCKDEV_SEL with offset IYL.
_blkCall:
push ix
call _blkCallAddr
; Before we call... is IX zero? We don't want to call a zero.
push af
ld a, ixh
add a, ixl
jr c, .ok ; if there's a carry, it isn't zero
cp 0
jr z, .error ; if no carry and zero, then both numbers are
; zero
xor a
cp ixh
jr nz, .ok ; not zero, ok
cp ixl
jr z, .error ; zero, error
.ok:
pop af
call callIX
jr .end
.error:
pop af
ld a, BLOCKDEV_ERR_UNSUPPORTED
@ -106,8 +109,23 @@ blkGetC:
; Repeatedly call blkGetC until the call is a success.
blkGetCW:
ld iyl, 0
call _blkCallAddr
.loop:
call callIX
jr nz, .loop
ret
; Reads B chars from blkGetC and copy them in (HL).
; Sets Z if successful, unset Z if there was an error.
blkRead:
.loop:
call blkGetC
jr nz, blkGetCW
ret nz
ld (hl), a
inc hl
djnz .loop
cp a ; ensure Z
ret
; Writes character in A in current position in the selected device. Sets Z
@ -133,8 +151,13 @@ blkSeek:
ld iyl, 4
jr _blkCall
; Returns the current position of the selected device in HL.
blkTell:
ld iyl, 6
jr _blkCall
; This label is at the end of the file on purpose: the glue file should include
; a list of device routine table entries just after the include. Each line
; has 3 word addresses: GetC, PutC and Seek. An entry could look like:
; .dw mmapGetC, mmapPutC, mmapSeek
; has 4 word addresses: GetC, PutC and Seek, Tell. An entry could look like:
; .dw mmapGetC, mmapPutC, mmapSeek, mmapTell
blkDevTbl:

10
parts/mmap.asm
View File

@ -11,6 +11,12 @@ MMAP_RAMEND .equ MMAP_PTR+2
; *** CODE ***
mmapInit:
xor a
ld (MMAP_PTR), a
ld (MMAP_PTR+1), a
ret
; Increase mem pointer by one
_mmapForward:
ld hl, (MMAP_PTR)
@ -54,3 +60,7 @@ mmapSeek:
ld (MMAP_PTR), hl
ret
mmapTell:
ld hl, (MMAP_PTR)
ret