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sdc: add second buffer
This commit is contained in:
Virgil Dupras
parent
db24e21276
commit
e046081900
100
kernel/sdc.asm
100
kernel/sdc.asm
@ -46,8 +46,6 @@
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; clean, we use any. This way, as long as writing isn't made to random
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; addresses, we ensure that we don't write wastefully because read operations,
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; even if random, will always use the one buffer that isn't dirty.
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;
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; NOTE: the 2-buffers thing is still a work in progress...
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; *** Defines ***
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; SDC_PORT_CSHIGH: Port number to make CS high
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@ -61,13 +59,18 @@
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; This is a pointer to the currently selected buffer. This points to the BUFSEC
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; part, that is, two bytes before actual content begins.
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.equ SDC_BUFPTR SDC_RAMSTART
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; Sector number currently in SDC_BUF.
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.equ SDC_BUFSEC SDC_BUFPTR+2
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; Sector number currently in SDC_BUF1.
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.equ SDC_BUFSEC1 SDC_BUFPTR+2
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; Whether the buffer has been written to. 0 means clean. 1 means dirty.
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.equ SDC_BUFDIRTY SDC_BUFSEC+1
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.equ SDC_BUFDIRTY1 SDC_BUFSEC1+1
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; The contents of the buffer.
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.equ SDC_BUF SDC_BUFDIRTY+1
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.equ SDC_RAMEND SDC_BUF+SDC_BLKSIZE
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.equ SDC_BUF1 SDC_BUFDIRTY1+1
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; second buffer has the same structure as the first.
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.equ SDC_BUFSEC2 SDC_BUF1+SDC_BLKSIZE
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.equ SDC_BUFDIRTY2 SDC_BUFSEC2+1
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.equ SDC_BUF2 SDC_BUFDIRTY2+1
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.equ SDC_RAMEND SDC_BUF2+SDC_BLKSIZE
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; *** Code ***
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; Wake the SD card up. After power up, a SD card has to receive at least 74
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@ -252,12 +255,12 @@ sdcInitialize:
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jr nz, .error
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; Success! out of idle mode!
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; initialize variables
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ld hl, SDC_BUFSEC
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ld hl, SDC_BUFSEC1
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ld (SDC_BUFPTR), hl
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ld a, 0xff
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ld (SDC_BUFSEC), a
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ld (SDC_BUFSEC1), a
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xor a
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ld (SDC_BUFDIRTY), a
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ld (SDC_BUFDIRTY1), a
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jr .end
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.error:
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@ -411,7 +414,7 @@ sdcWriteBlk:
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; good! Now, we need to let the card process this data. It will return
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; 0xff when it's not busy any more.
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call sdcWaitResp
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; Success! Now let's unset the first flag
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; Success! Now let's unset the dirty flag
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ld hl, (SDC_BUFPTR)
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inc hl ; dirty flag
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xor a
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@ -430,26 +433,53 @@ sdcWriteBlk:
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pop hl
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ret
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; Ensures that the sector of the current buffer is in sync with HL, that is,
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; that the current buffer in memory corresponds to where HL points to in the SD
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; card. If it doesn't, loads the sector specified in the highest 7 bits of HL
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; in memory and update the buffer's sector.
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; Considering the first 7 bits of HL, select the most appropriate of our two
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; buffers and, if necessary, sync that buffer with the SD card. If the selected
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; buffer doesn't have the same sector as what HL asks, load that buffer from
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; the SD card.
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; If the dirty flag is set, we write the content of the in-memory buffer to the
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; SD card before we read a new sector.
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; Returns Z on success, not-Z on error (with the error code from either
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; sdcReadBlk or sdcWriteBlk)
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sdcSync:
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; HL points to the character we're supposed to read or right now,
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; but we first have to check whether we need to load a new sector in
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; memory. To do this, we compare the high 7 bits of HL with
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; the buffer's sector. If they're different, we need to load a new block.
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; HL points to the character we're supposed to read or right now. Let's
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; extract the wanted sector from this.
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ld a, h
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srl a ; A --> the requested sector number
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push hl ; <|
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ld hl, (SDC_BUFPTR) ; | HL points to sector number
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cp (hl) ; |
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pop hl ; <|
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ret z ; equal? nothing to do
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push hl ; Save the requested addr for later
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ld l, a
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; Let's first see if our first buffer has our sector
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ld a, (SDC_BUFSEC1)
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cp l
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jr z, .buf1Ok
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; Ok, let's check for buf2 then
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ld a, (SDC_BUFSEC2)
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cp l
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jr z, .buf2Ok
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; None of our two buffers have the sector we need, we'll need to load
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; a new one.
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; We select our buffer depending on which is dirty. If both are on the
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; same status of dirtiness, we pick any (the first in our case). If one
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; of them is dirty, we pick the clean one.
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ld hl, SDC_BUFSEC1
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ld a, (SDC_BUFDIRTY1)
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or a ; is buf1 dirty?
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jr z, .ready ; no? good, that's our buffer
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; yes? then buf2 is our buffer.
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ld hl, SDC_BUFSEC2
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.ready:
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; At this point, HL points to one of our two buffers, the good one.
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; Let's save it to SDC_BUFPTR
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ld (SDC_BUFPTR), hl
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; You remember that HL we saved a long time ago? Now's the time to
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; bring it back.
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pop hl
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; We have to read a new sector, but first, let's write the current one
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; if needed.
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call sdcWriteBlk
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@ -459,6 +489,17 @@ sdcSync:
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srl a
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jp sdcReadBlk ; returns
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.buf1Ok:
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ld hl, SDC_BUFSEC1
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ld (SDC_BUFPTR), hl
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pop hl
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ret
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.buf2Ok:
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ld hl, SDC_BUFSEC2
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ld (SDC_BUFPTR), hl
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pop hl
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ret
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; *** shell cmds ***
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@ -470,6 +511,12 @@ sdcInitializeCmd:
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; Flush the current SDC buffer if dirty
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sdcFlushCmd:
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.db "sdcf", 0, 0, 0
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ld hl, SDC_BUFSEC1
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ld (SDC_BUFPTR), hl
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call sdcWriteBlk
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ret nz
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ld hl, SDC_BUFSEC2
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ld (SDC_BUFPTR), hl
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jp sdcWriteBlk ; returns
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; *** blkdev routines ***
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@ -528,8 +575,11 @@ sdcPutC:
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pop af
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ld (hl), a
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; Now, let's set the dirty flag
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ld a, 1
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ld (SDC_BUFDIRTY), a
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ld hl, (SDC_BUFPTR)
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inc hl ; point to dirty flag
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ld (hl), a ; set dirty flag
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xor a ; ensure Z
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jr .end
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.error:
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@ -1,6 +1,6 @@
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.equ USER_CODE 0x8600
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.equ USER_RAMSTART USER_CODE+0x1800
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.equ FS_HANDLE_SIZE 8
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.equ FS_HANDLE_SIZE 6
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.equ BLOCKDEV_SIZE 8
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; *** JUMP TABLE ***
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@ -16,13 +16,12 @@
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.equ parseHex 0x1e
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.equ parseHexPair 0x21
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.equ blkSel 0x24
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.equ fsFindFN 0x27
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.equ fsOpen 0x2a
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.equ fsGetC 0x2d
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.equ fsSeek 0x30
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.equ fsTell 0x33
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.equ blkSet 0x27
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.equ fsFindFN 0x2a
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.equ fsOpen 0x2d
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.equ fsGetC 0x30
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.equ cpHLDE 0x33
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.equ cpHLDE 0x3b
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.equ parseArgs 0x3e
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.equ printstr 0x41
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.equ _blkGetC 0x44
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@ -23,18 +23,17 @@
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jp parseHex
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jp parseHexPair
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jp blkSel
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jp blkSet
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jp fsFindFN
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jp fsOpen
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jp fsGetC
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jp fsSeek
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jp fsTell ; approaching 0x38...
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jp cpHLDE ; approaching 0x38...
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; interrupt hook
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.fill 0x38-$
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jp aciaInt
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; *** Jump Table (cont.) ***
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jp cpHLDE
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jp parseArgs
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jp printstr
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jp _blkGetC
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@ -1,6 +1,6 @@
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.equ USER_CODE 0x8600
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.equ USER_RAMSTART USER_CODE+0x1800
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.equ FS_HANDLE_SIZE 8
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.equ FS_HANDLE_SIZE 6
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.equ BLOCKDEV_SIZE 8
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; *** JUMP TABLE ***
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@ -16,13 +16,12 @@
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.equ parseHex 0x1e
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.equ parseHexPair 0x21
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.equ blkSel 0x24
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.equ fsFindFN 0x27
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.equ fsOpen 0x2a
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.equ fsGetC 0x2d
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.equ fsSeek 0x30
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.equ fsTell 0x33
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.equ blkSet 0x27
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.equ fsFindFN 0x2a
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.equ fsOpen 0x2d
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.equ fsGetC 0x30
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.equ cpHLDE 0x33
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.equ cpHLDE 0x3b
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.equ parseArgs 0x3e
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.equ printstr 0x41
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.equ _blkGetC 0x44
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