Disk II Boot Disassembly

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Michael J. Kelly

Mar 29, 2000, 3:00:00 AM3/29/00
Ok, folks. I recall there being a file somewhere called "THE.BOOT.PROCESS"
which described in detail what happens from $C600 (start of boot) to
preliminary DOS initialization. I actually had several copies here at
the home printed out, but now I don't know where they went and I cannot
find this disassembly ANYWHERE. I *swear* it was on grin.net/cturley's
archive somewhere, but now I'm just at a loss. (Actually, I think
it was in A2.GRAND.CENTRAL, but that directory now seems to be empty..?)

I've found "DOS.COLDSTART.txt", but that only describes the process
from boot stage 2 of the loader.

Does *anyone* know what I'm talking about, or could give me some pointers?

Thanks in advance.


mo...@whiskers.com ()__() || I think so, Brain, but if they called
http://www.whiskers.com (oo) || them "Sad Meals", kids wouldn't buy
==()== || them!

Paul R. Santa-Maria

Mar 30, 2000, 3:00:00 AM3/30/00
I have a commented disassembly of the boot ROMs (comments from Beneath
Apple DOS) that I made for my own reference.

Paul R. Santa-Maria
Ann Arbor, Michigan USA

Michael J. Kelly <mj...@intelsrv2.cs.uofs.edu> wrote in article


Mar 30, 2000, 3:00:00 AM3/30/00
Here's the URL for it:


It's also on the Ground site and is from the same ref. source that Paul
mentioned in his reply.


PS: The A2.Grand.Central.Station folder is empty now because I'm
adding to and updating the links in that old html document.

Michael 'AppleWin Debugger Dev'

Jun 30, 2016, 5:40:48 AM6/30/16
On Thursday, March 30, 2000 at 1:00:00 AM UTC-7, Cturley2 wrote:
> Here's the URL for it:
> .PROCESS.txt

Necro'ing this ancient thread in case anyone comes here searching for "C600 disassembly" and gets frustrated at finding the dead link for Charles T. 'Dr. Tom' Turle's excellent "DOS 3.3 Anatomy" commentary.

Working link:

It is also mirrored at textfiles, except annoyingly BOOT.PROCESS.txt is missing (I've already emailed Jason Scott)

- - - 8< BOOT.PROCESS.txt - - -

* *
* *
* *
* The following disassembly describes the boot process for *
* a slave disk. In order to TRULY understand this listing, you *
* should first be familiar with the exact sequence and coding of *
* disk bytes used in track formatting. This information can be *
* found in chapter 3 of the book BENEATH APPLE DOS. (The *
* distinctions between booting a slave disk versus a master disk *
* are described in chapter 8 of the same reference.) *
* The boot process loads DOS into the machine as a series *
* of discrete packages. After each package is loaded, it is *
* executed to load in the next section of DOS. The last *
* instruction of the boot process jumps into DOS's coldstart *
* routine to build the DOS buffers, set up the page-three vector *
* table and run the "HELLO" program. *
* Because DOS is loaded in stages, any protected disk can *
* cracked by tracing the boot. If you modify each section of *
* the boot to stop after loading the next section, you can *
* inspect the different stages of the boot to discover the *
* protection scheme(s) used. (P.S. In order to modify BOOT0, *
* you must first move it down to a RAM location defined by: *
* $hs00, where h = high nibble of an address that is low enough *
* to accomodate DOS in free memory above and, s = present slot *
* number housing the disk controller card.) *
* *

* *
* BOOT 0 *
* *
* *
* - relocatable code resident on the disk controller's ROM. *
* - because the code is relocatable, the disk controllers card *
* can be used in different slots. Execution begins at $Cs00, *
* where s = slot number (ex. $C600 for card in slot 6). *
* - When BOOT0 is executed it: *
* (1) builds a table of indices which are used to convert *
* the disk bytes into 6/2 encoded bytes which are *
* needed by RWTS to translate the disk bytes into *
* normal memory bytes. *
* (2) recalibrates the disk arm by moving it to trk0/sec0. *
* (3) reads BOOT1 into $800 to $8FF (from trk0/sec0). *
* (4) jumps to $801 to begin the execution of BOOT1. *
* *

BOOT0 LDX #$20 ;Controller card's identification byte.

* Construct a read-translate table which
* we will need to convert disk bytes to
* encoded memory bytes. (The encoded memory
* bytes later go trough further decoding to
* convert them to normal memory bytes.)
* We construct the table by sequentially
* incrementing (x) and testing it to see
* if it meets the folowing criteria of a
* disk byte:
* (1) it must have at least one pair of
* adjacent 1's in bits 0 to 6.
* (2) it must not have more than one pair
* of adjacent 0's in bits 0 to 6.
* (Note that we use the x-value to represent
* only the lower seven bits of a disk byte
* because all disk bytes are negative.)
* Each time we find an (x) that represents
* a simulated disk byte, we increment (y).
* (Y) is then placed in the read table at an
* offset of (x) from the beginning of the table.
* The table generated is shown below. The
* empty bytes represent offsets where (x)
* did not meet the criteria of a disk byte.
* The values in parentheses represent the
* (x)-values tested.
* 36C- 00 01 -- --
* (16) (17) (18) (19)
* 370- 02 03 -- 04 05 06 -- --
* (1A) (1B) (1C) (1D) (1E) (1F) (20) (21)
* 378- -- -- -- -- 07 08 -- --
* (22) (23) (24) (25) (26) (27) (28) (29)
* 380- -- 09 0A 0B 0C 0D -- --
* (2A) (2B) (2C) (2D) (2E) (2F) (30) (31)
* 388- 0E 0F 10 11 12 13 -- 14
* (32) (22) (34) (35) (36) (37) (38) (39)
* 390- 15 16 17 18 19 1A -- --
* (3A) (3B) (3C) (3D) (3E) (3F) (40) (41)
* 398- -- -- -- -- -- -- -- --
* (42) (43) (44) (45) (46) (47) (48) (49)
* 3A0- -- 1B -- 1C 1D 1E -- --
* (4A) (4B) (4C) (4D) (4E) (4F) (50) (51)
* 3A8- -- 1F -- -- 20 21 -- 22
* (52) (53) (54) (55) (56) (57) (58) (59)
* 3B0- 23 24 25 26 27 28 -- --
* (5A) (5B) (5C) (5D) (5E) (5F) (60) (61)
* 3B8- -- -- -- 29 2A 2B -- 2C
* (62) (63) (64) (65) (66) (67) (68) (69)
* 3C0- 2D 2E 2F 30 31 32 -- --
* (6A) (6B) (6C) (6D) (6E) (6F) (70) (71)
* 3C8- 33 34 35 36 37 38 -- 39
* (72) (73) (74) (75) (76) (77) (78) (79)
* 3D0- 3A 3B 3C 3D 3E 3F -- --
* (7A) (7B) (7C) (7D) (7E) (7F)

(Cs02) LDY #0 ;Initialize the (y) index.
(Cs04) LDX #3 ;"3" is used for controller ID. Any number
;between 0 and #$16 could be used. Except
;for ID purposes, the operand isn't even
;relevant until it is #$16 (dec #22).
BUILDTBL STX BT0SCRTH ;Save potential index seed in the zero page.

* Transfer (x) to (a) and test to see if it
* meets the following disk byte criteria:
* (1) has at least one pair of adjacent 1's
* in bits 0 to 6.
* (2) has no more than one pair of adjacent
* 0's in bits 0 to 6.

* Test for adjacent 1's.
* Note: by comparing a shifted version of
* the seed (in accumulator) with the original
* version of the seed (in BT0SCRTH, $3C) we are
* actually testing adjacent bits as shown below:
* Shifted: b6 b5 b4 b3 b2 b1 b0 0
* Orignal: b7 b6 b5 b4 b3 b2 b1 b0
* -----------------------------------
* Testing: b6,7 b5,6 b4,5 b3,4 b2,3 b1,2 b0,1 -

(Cs08) TXA
(Cs0A) BIT BT0SCRTH ;Conditions the z-flag of the status.
;(If any bits match, z-flag=1.)
(Cs0C) BEQ GETNEWX ;Branch if value was illegal.
;Illegal value = z-flag=1 = no match = no
;adjacent 1's.

* Got at least 1 pair of adjacent 1's, so
* now prepare to test for adjacent 0's.
* (Note: the previous "BIT" instruction
* alters the z-flag in the status but
* does not affect the accumulator.)
(Cs0E) ORA BT0SCRTH ;Merge shifted version of seed with orig.
(Cs10) EOR #$FF ;Take 1's compliment of shifted version to
;swap 1's for 0's and 0's for 1's.
(Cs12) AND #%01111110 ;Throw away the hi and least significant
;bits so will be testing:
; b5,6 b4,5 b3,4 b2,3 b1,2 b0,1.

* Test for pairs of adjacent 0's.
* Remember, only 1 pair of adjacent 0's is
* allowed. Because we did a 1's compliment
* of the merged bits above, a SET BIT NOW
* therefore test for a pair of adjacent 0's
* by shifting a bit into the carry:
* - if (c) = 1 = at least one pair of adjacent 0's
* is present.
* - if (c) = 1 AND the remaining byte = 0 then
* we have only one pair of adjacent 0's so
* value is legal.
* - if (c) = 1 AND the remaining byte < > 0, we
* have more than one pair of adjacent 0's so
* value is illegal.
TESTCARY BCS GETNEWX ;Always fall through on very first entry.
;If branch is taken, got illegal value
;because more than 1 pr of adjacent 0's.
(Cs16) LSR ;Shift a bit into the carry (if carry set
;have at least 1 pr of adjacent 0's).
(Cs17) BNE TESTCARY ;Take branch when remaining byte is not
;zero. Got at least 1 pr of adjacent 0's.
;Go test carry to see if another pair has
;already been detected.

* Index byte was legal. We either got no
* adjacent 0's or else only one pair of
* adjacent 0's.
(Cs19) TYA ;Store the counter that corresponds to a
(Cs1A) STA BTNIBL-$16,X ;legal nibble. The first (x) value used
;is #$16, last is #$7F. The first (y) value
;stored is 0, the last is #$3F.
(Cs1D) INY
(Cs1F) BPL BUILDTBL ;Keep on trying to build table until (x)
;increments to #$80.

* Find out which slot the disk controller
* card resides in.
(Cs21) JSR MONRTS ;Jsr to an RTS to put the present address on
;the stack. The hi byte of the present addr
;($Cs) tells us what slot (s) the card is
;located in.

* An RTS instruction in monitor ROM.

(Cs24) TSX ;Put the value of the stack pointer in (x).
(Cs25) LDA STACK,X ;Get the hi byte of the controllers address
;($Cs) from the stack.
(Cs28) ASL ;Multiply by 16 (throwing away original hi
ASL ;nibble) so we are left with #$s0.
ASL ;(a) = slot * 16.
STA SLT16ZPG ;Save slot*16 in a zero-page location.
(Cs2E) TAX ;Set (x) = slot * 16 so we can index the
;base addresses associated with the drive
(Cs2F) LDA Q7L,X ;Set the READ mode.
LDA SELDRV1 ;Select drive 1.
(Cs38) LDA MTRON,X ;Spin the disk.

* Move disk arm to track 0 by doing a
* recalibration. (That is, force the arm
* against the stop by pretending that it
* is presently at trk decimal 40.)
* (The arm is moved by sequentially turning
* a series of magnets off and on.)
(Cs3B) LDY #80 ;Pretend arm is at trk40 (dec 80 half-trks).
MAGNTOFF LDA MAG0FF,X ;Turn the presently aligned magnet off.
(Cs40) TYA ;Calculate the next magnet that should be
;turned on to suck the arm over.
(Cs41) AND #%00000011 ;Only keep the lower two bits because we
;only want a maximum value of 3 because
;there are only 4 magnets (which are indexed
;by values 0 to 3). The sequence used in
;this loop is: 3,2,1,0,3...
(Cs43) ASL ;Multiply by 2 so the index is directed to
;an address that turns a magnet ON. The
;sequence used is: 6,4,2,0,6...0.
(Cs44) ORA SLT16ZPG ;Merge the index with the slot * 16 value.
TAX ;Put the calculated index in (x).
LDA MAG0N,X ;Turn the appropriate magnet ON.
(Cs4A) LDA #$56 ;Delay approximately 20 000 machine cycles
;(approximately 20 milliseconds.) (Gives
(Cs4C) JSR WAIT ;arm time to align with energized magnet
;and reduces overshoot or bounce.)

* Monitor ROM's main delay routine.
* Delay z number of cycles based on
* the formula:
* z = ((5 * a^2) + (27 * a) +26) / 2
* where a = value in the accumulator on entry.
WAIT SEC ;Prepare for subtraction.
WAIT2 PHA ;Save (a) on the stack.
WAIT3 SBC #1 ;Keep on reducing (a) until it equals 0.
SBC #1 ;Reduce the original (a) down to 0 again.

(Cs4F) DEY ;Reduce trk # count.
(Cs50) BPL MAGNTOFF ;Not at trk0 yet, so go move arm some more.

* Initialize the buffer pointer and trk/sec values.
* (On entry: (x) = slot *16, (y) = #$FF & (a) = $00.)
(Cs52) STA PT2BTBUF ;Set the low byte of the buf pointer to $00.
STA BOOTSEC ;Initialize for sector 0 on track 0.
LDA #8 ;Set the hi byte of the buf pointer to $08
(Cs5A) STA PT2BTBUF+1 ;(that is, direct pointer at $800).

* Prepare to start reading a prologue.
BTRDSEC CLC ;(c) = 0 = signal to read an addr prologue.

* Begin reading a prologue.
PRSRVFLG PHP ;Preserve the status denoting if reading
;address ((c)=0) or data ((c)=1) prologue.

* Look for an address prologue ("D5 AA 96")
* or a data prologue ("D5 AA AD").
STARTSEQ LDA Q6L,X ;Read a disk byte.
BPL STARTSEQ ;Wait for a full byte.
BTRYD5 EOR #$D5 ;Is it a "D5"?
BNE STARTSEQ ;No - restart sequence.
BTRYAA LDA Q6L,X ;Read next byte in header.
BPL BTRYAA ;Wait for a full byte.
CMP #$AA ;Is it an "AA"?
BNE BTRYD5 ;No - restart sequence.
NOP ;Delay 2 cycles.
BTRY96 LDA Q6L,X ;Read third byte in header.
BPL BTRY96 ;Wait for a full byte.
CMP #$96 ;Is it a "96"?
Cs78) BEQ RDVLTKSC ;Found an address prologue, so now go read
;the vol, trk, sec values in the header.

* The first two bytes were "D5 AA".
* The 3rd byte was not "96". Therefore,
* although we know this isn't an address
* prologue, maybe it is a data prologue.
(Cs7A) PLP ;Get the status back off the stack so we can
;check if we were looking for an address or
;data prologue.
(Cs7B) BCC BTRDSEC ;Branch back to try again if we were looking
;for an address prologue but didn't find it.

* We were looking for a data prologue so
* now compare the 3rd byte with that of a
* data prologue.
BTRYAD EOR #$AD ;Is it an "AD"?
BEQ RDBTDATA ;Yes - found data prol so now read in data.
(Cs81) BNE BTRDSEC ;No - go try again to find sequence 4 data.

* Read volume, track and sector values in
* the address header.
* Remember, @ of these pieces of information
* are housed in two bytes in an odd-even encoded
* format: 1rst byte: 1 b7 1 b5 1 b3 1 b1 (odd-encoded).
* 2nd byte: 1 b6 1 b4 1 b2 1 b1 (even-encoded).
* We must decode these bytes to check if we located
* the correct volume, track and sector.
RDVLTKSC LDY #3 ;Set counter for 3 decoded bytes.
MOREBYTS STA BOOTEMP ;Only relevant the last time through the
(Cs85) ;loop at which time it contains the decoded
(Cs87) ;track number read off the disk.
BTRDODD LDA Q6L,X ;Read odd-encoded byte.
BPL BTRDODD ;Wait for a full byte.
(Cs8C) ROL ;Throw away the hi bit & shift the odd bits
;to their regular position.
(Cs8D) STA BT0SCRTH ;Save realigned version of odd-encoded byte.
BTRDEVEN LDA Q6L,X ;Read the even-encoded byte.
BPL BTRDEVEN ;Wait for a full byte.
AND BT0SCRTH ;Merge the two bytes.
DEY ;Reduce counter for # of bytes to rebuild.
BNE MOREBYTS ;Branch if more bytes to patch back together.
PLP ;Throw the status on the stack away.
CMP BOOTSEC ;Is the sector read = sector wanted?
BNE BTRDSEC ;No - go back to find correct sector.
LDA BOOTEMP ;Get decoded trk # just read off disk.
CMP BOOTRK ;Is trk found = trk wanted?
BNE BTRDSEC ;No - go back to try again.
(CsA4) BCS PRSRVFLG ;ALWAYS - just read addr field, so now go
; read the data prologue.

* Read the sector's data bytes.

* Read the first 86 ($56) bytes of the sector. Use
* the disk byte as an index to the BTNIBL table ($36C-$3D5).
* Get the value from BTNIBL table & EOR it with the
* previous EOR result (except on entry, use
* #0 EOR BTNIBL-$96,Y) to produce a 2-encoded nibble.
* (On entry, (a) = 0.)
BTRDATA LDY #$56 ;Read $56 (dec #86) bytes.
KEEPCNT1 STY BT0SCRTH ;Save the counter.
RDDSK1 LDY Q6L,X ;Read a disk data byte.
BPL RDDSK1 ;Wait for a full byte.
(CsAF) EOR BTNIBL-$96,Y ;Use disk byte as an index to the table
;and EOR to decode to a 2-encoded nibble.
(CsB2) LDY BT0SCRTH ;Retrieve the counter.
DEY ;Reduce the counter (& condition z-flag).
STA BUF300,Y ;Store 2-encoded nibble in page 3 buffer.
(CSB8) BNE KEEPCNT1 ;Branch if more bytes to read.

* Read the rest of the sector (256 disk bytes
* remaining). Use disk byte as an index to BTNIBL
* table. Get value from nibble table and EOR it
* with previous EOR result to yeild a 6-encoded
* nibble. (On entry, (y) = 0.)
KEEPCNT2 STY BT0SCRTH ;Set disk byte counter = 0.
RDDSK2 LDY Q6L,X ;Read a disk byte.
BPL RDDSK2 ;Wait for a full byte.
(CsC1) EOR BTNIBL-$96,Y ;Use disk byte as an index to the nibble
;table and EOR it with previous result to
;produce a 6-encoded nibble.
(CsC4) LDY BT0SCRTH ;Get index to buffer.
STA (PT2BTBUF),Y ;Store 6-encoded nibble in buffer.
INY ;Kick up offset into buffer.

* Read and test the data checksum.
* On entry, (a) = result of previous cummulative
* EORing. Therefore, any non-cancelling errors are
* detected at the BNE instruction below.
RDCK LDY Q6L,X ;Read the data checksum.
BPL RDCK ;Wait for a full byte.
(CsD0) EOR BTNIBL-$96,Y ;EOR byte read with the previous
;cummulative result.
TSTRERD BNE BTRDSEC ;Bad checksum so branch back to re-read.
(CsD3) ;(Also branches to here if got a good read
;but there are more sectors to read if the
;first byte of BOOT1 is modified to allow
;BOOT0 to read more than 1 sector (see
;comments below).

* Convert 6-and-2 encoded buffer bytes to
* normal 8-bit memory bytes.
(CsD5) LDY #0 ;Initialize index to target memory byte.
SETX56 LDX #$56 ;Set index to buf containing encoded bytes.
DOWNX DEX ;Reduce index for next buffer byte.
BMI SETX56 ;Reset index to encoded buffer.
LDA (PT2BTBUF),Y ;Get (a) = 6-encoded nibble.
LSR BUF300,Y ;Put a bit from the 2-encoded buffer in (c)
ROL ;and then roll it into the 6-encoded nibble.
LSR BUF300,Y ;Do the same with the next bit of the pair.
STA (PT2BTBUF),Y ;Store the re-constructed 8-bit byte in memory.
INY ;Increase the offset to the buffer.
(CsE9) BNE DOWNX ;Branch back if more bytes to reconstruct.

* Prepare to read in the next sector.
* NOTE: Normaly only trk0/sec0 (which
* represents BOOT1) is read in by BOOT0.
* The number of sectors read in by BOOT0 is
* determined by the first byte of BOOT1.
* Whereas BOOT1 resides in memory on an 48K
* INITed disk at $B600 - $B6FF, we can zap a
* disk at $B600 with the # of sectors we
* we would like BOOT0 to read in if we want
* it to read in more than 1 sector.
(CsEB) INC PT2BTBUF+1 ;Just crossed page boundary, so kick up
;the hi byte of the target address.
(CsED) INC BOOTSEC ;Set value for next sector wanted.
LDA BOOTSEC ;Get next sector wanted.
(CsF1) CMP $800 ;Test if read enough sectors.
;First byte of image of BOOT1 normally
;contains #$01 which denotes only 1 sector
;(sec0/trk0) should be read in by BOOT0.
(CsF4) LDX SLT16ZPG ;(x) = slot *16.
BCC TSTRERD ;Branch back to read more sectors.
(CsF8) JMP BT1EXC08 ;Jumps into BOOT1 (which was copied into
------------ ;page 8 from trk0/sec0) to begin execution
;of BOOT1.

* *
* BOOT 1 *
* *
* *
* - stored on trk0/sec0. *
* - IMAGE in memory on a 48K system resides at $B600 - $B6FF. *
* - read into $800 to $8FF by the disk controller ROM (BOOT0). *
* - execution begins at $801 & uses the controller's read sector *
* subroutine (BTRDSEC, Cs00, where s = slot # of card) to read *
* in trk0/sec9 down to trk0/sec1 ($BFFF --> $B600). *
* - NOTE: In order to generate an accurate symbol table that *
* can be applied 2 both the formatted & linear disassemblies, *
* and because different assemblers vary in their abilities to *
* accept certain OBJect values or re-ORG during assembly, the *
* following special label system has been created: *
* Image label/adr Execution label/adr Comments *
* --------------- ------------------- -------------------- *
* SEC2RDB6, $B600 SEC2RD08, $800 ;Defines # of secs to *
* ;be read in by boot0. *
* BT1EXCB6, $B601 BT1EXC08, $801 ;Start of boot1. *
* ;Boot0 jumps to this *
* ;location. *
* SKPRELB6, $B61F SKPREL08, $81F ;Target labl 4 brnch. *
* PRP4B2B6, $B639 PRP4B208, $839 ;Target labl 4 brnch. *
* IMG8FD, $B6FD BT1LDADR, $8FD ;Boot1 load address. *
* ;Varies from $B600 to *
* ;$BF00. Eventually *
* ;pts 2 start of boot2 *
* ;($B700). *
* IMG8FF, $B6FF BT1PG2RD, $8FF ;Contains # of secs 2 *
* ;be read in when *
* ;executing boot1. Also*
* ;doubles as logical *
* ;sec #. Varies from: *
* ;$09 --> $00 --> $FF. *
* - As indicated above, SEC2RD08 ($800) defines the number of *
* sectors to be read in by boot0. This value is normally $01 *
* (meaning read only sector0 of track0). However, you can zap *
* trk0/sec0/offset0 with a larger value ($01 to $10) to read *
* more sectors from trk0. Also note that most references say *
* that SEC2RD08 normally contains a "$00" (rather than a *
* "$01"). Because the test at $CsF6 uses the carry, either *
* value will only cause one sector to be read in. However, *
* "$01" is the value used by DOS. (Confusion may stem from *
* the fact that Applesoft later stores a $00 in memory at *
* $800.) *
* *

(B600) <============= image address.
(800) <============== execution address.
SEC2RD08 HEX 01 ;Defines the number of sectors to be read
;in from track 0 during BOOT0.

BT1EXC08 LDA PT2BUF+1 ;Get the next page to read in.
CMP #$09 ;Is it page 9 (ie. first page read by BOOT1)?
BNE SKPREL08 ;No - already used by BOOT1 to read page 9,
;so skip pointer initialization given below.

* Initialize the pointer (PT2RDSC) to point
* at BOOT0's read sector subroutine (BTRDSEC,
* $Cs5C, where s = slot #, normally $C65C).
(807) LDA SLT16ZPG ;(a) = slot *16.
LSR ;Divide by 16.
ORA $C0 ;Merge with $C0 to get $Cs, where s=slot#.
STA PTR2RDSC+1 ;Store the hi byte of the address of the
;controller's read sector subroutine.
LDA #<BTRDSEC ;Get low byte of addr of subroutine.
STA PTR2RDSC ;Low byte is a constant (#$5C) and is
;therefore not variable with the slot used
;(as is the hi byte).

* Read in the 9 sectors represented by
* trk0/sec9 down to trk0/sec1 into
* $BFFF to $B600. Note that the sectors
* are read in from higher to lower memory.
* These sectors contain the IMAGE of BOOT1,
* part of the File Manager and almost all
* of RWTS and it's associated routines.

* Calculate target address for the first sector
* to be read in.
(815) CLC
LDA BT1LDADR+1 ;Contains $B6 on 48K slave.
ADC BT1PG2RD ;Contains #$09 on 48K slave.
STA BT1LDADR+1 ;(a) = #$BF on 48K slave.

* Determine the number of sectors left to read,
* the physical sector number & the target address.
* Then, go read in the next sector.
SKPREL08 LDX BT1PG2RD ;(x) = pages left to read in less 1.
;(Also doubles as logical sector number.
;Varies from $09 --> $FF.)
BMI PRP4B208 ;When (x) = $FF, we have read all the
;sectors in so go exit.
LDA PHYSECP8-$AE00,X ;Convert the logical sector number
;to a physical sector number. (Equivalent
;to "LDA $84D,X".)
STA BOOTSEC ;Store physical sector number in page0.
DEC BT1PG2RD ;Reduce sectors (pages) left to read for
;the next time around.
LDA BT1LDADR+1 ;Point the buffer pointer at the target
STA PT2BTBUF+1 ;address. (Varies from $BF to $B6 on a
;48K slave.)
DEC BT1LDADR+1 ;Reduce the hi byte of the I/O buffer for
;the next time around. (Varies from $BF to
;$B5 on a 48K slave.)
LDX SLT16ZPG ;Set (x) = slot*16.
(836) JMP (PTR2RDSC) ;Equivalent to "JMP ($8FD)" or "JMP $Cs5C"
(B636) ------------ ;to go read in the next sector.
;***************** NOTE *******************
;* IS READ IN. (BT1EXCB6 is a carbon copy *
;* of BT1EXC08.) *

* Prepare for BOOT2.
PRP4B208 INC BT1LDADR+1 ;Point at the load address for BOOT2.
INC BT1LDADR+1 ;(After the INCs = $B7 on 48K slave.)

* Set full screen text & designate the
* keyboard and screen as the I/O devices.
(83F) JSR SETKBD ;Simulate an IN#0. (See dis'mbly below.)
JSR SETVID ;Simulate an PR#0. (See dis'mbly below.)
JSR INIT ;Simulate a "TEXT" statement. (See dis'mbly
LDX SLT16ZPG ;(x) = slot * 16.

* Go to BOOT2.
(84A) JMP (BT1LDADR) ;Jump to BOOT2 ($B700 on 48K slave).

* *
* BOOT2 *
* *
* *
* - Reads in the rest of DOS starting at trk02/sec04 down to *
* trk00/sec0A ($B5FF --> $9B00). (P.S. Sectors 0A and 0B of *
* track 0 are empty ($9CFF - $9B00).) *
* - After the rest of DOS is read in, execution jumps to DOS's *
* coldstart routine (DOSCLD, $9D84). *
* - Note that on entry: (x) = slot * 16 *
* *

* Prepare RWTS's input-output block (IOB)
* and designate the number of sectors to read.
BOOT2 STX IBSLOT ;(x) = slot*16 wanted.
STX IOBPSN ;Last-used slot*16 value.
LDA #1 ;Set both the last-used and wanted drives
STA IOBDPDN ;as drive #1.
LDA NMPG2RD ;Set number of pages (ie. secs) to read.
STA BT2PGCTR ;Counter for for number of pages to read.
LDA #2 ;Start with trk02/sec04.
LDA #4
(B71E) LDY BT1MGADR+1 ;(y) = hi byte of the address of the image
;of BOOT1 (#$B6 on a 48K slave).
(B721) DEY ;Define I/O buf as 1 page below boot1.
LDA #1 ;Opcode for read.

* Convert from (x) = slot*16 to (x) = slot.
(B72A) TXA ;(x) = slot * 16.
LSR ;Divide by 16.
(B72F) TAX ;(x) = slot.

* Initialize the page-four locations with
* the track numbers associated with the drives.
(B730) LDA #0

* Call the routine to read in the rest of DOS.

* READ/write a group of pages.
RWPAGES LDA ADROFIOB+1 ;Init (a)/(y) with the hi/low bytes of the
LDY ADROFIOB ;addr of RWTS's IOB for entry to RWTS.
(B799) JSR ENTERWTS ;Enter RWTS to read/write sector.

* Entry to RWTS.
ENTERWTS PHP ;Save status register on the stack.
(B7B6) SEI ;Set the interrupt disable flag to prevent
;any further maskable interrupts when doing
;real-time programming.
(B7B7) JSR RWTS ;Enter RWTS proper to do the operation:
; $00=seek, $01=read, $02=write, $03=format.

* RWTS proper.
(See dis'mbly in RWTSDRVR using READ.)

(B7BA) BCS ERRENTER ;Operation was NOT successful.
PLP ;Retrieve saved status off the stack.

ERRENTER PLP ;Throw the saved status off the stack.
SEC ;Signal operation was unsuccessful.
(B7C1) RTS

(B79C) LDY IBSECT ;Get # of the sector just read or written.
(B79F) DEY ;Set value for next sector 2 read. When
;executing BOOT1, goes from $09 to $FF.
(B7A0) BPL SAMETRK ;Branch to use the same track.

* Start a new track.
(B7A2) LDY #$0F ;Start with sector 15.
(B7A6) DEC IBTRK ;Reduce number of track wanted.

* Reduce the addr of the target memory location.
* Test if more sectors to read.
SAMETRK STY IBSECT ;Store the sector wanted.
DEC IBBUFP+1 ;Reduce buf addr of target memory location.
DEC BT2PGCTR ;Reduce counter for # of sectors to read.
BNE RWPAGES ;More sectors to read.
(B7B4) RTS

(B73B) LDX #$FF ;Completely clear out the stack.
STX IBVOL ;Set the volume to $FF (compliment of 0).

* Patch to clobber the language card
* and set video output.
CLOBCARD JSR SETVID ;Select the video screen.

* Monitor ROM's routine to designate the
* video screen as the output device.
* (Simulate a "PR#0" statement.)
SETVID LDA #0 ;Designate slot 0.
OUTPRT LDX #<CSW ;Set offset from start of zero page to OUTPUT hook.
AND #$0F

IOPRT1 LDA #>COUT1 ;(Hi byte of addr of KEYIN & COUT1 are equal.)

(BFCB) LDA $C081 ;Write enable the RAM card.
LDA $C081 ;(Read motherboard / write card bank 2.)
LDA #0 ;Set the language identifying byte on the
(BFD3) STA BASICCLD ;card to $00 so if card is tested (during
;an FP command), the machine will be forced
;to use the motherboard version of FP.
(BFD6) JSR CONTCLOB ;Now clobber the 80-column card.

* Clobber the 80-column card.
CONTCLOB LDA #$FF ;Set the mode flag for card.
STA $4FB ;Scratch pad memory for slot 3 peripheral.
STA $C00C ;Turn off the alternate character set.
(BA81) JMP INIT ;Simimulate a TEXT statement.

* Monitor ROM's Init routine.
- simulate a text statement.
(Ie. set window to full screen text.)

(BFD9) JMP BK2BOOT2 ;Return to original part of BOOT2.

* Return back to original part of BOOT2.
BK2BOOT2 JSR SETKBD ;Select the keyboard.

* Monitor ROM's routine to designate the
* keyboard as the input device.
* (Simulate a "IN#0" statement.)
SETKBD LDA #0 ;Pretend using slot 0.
INPRT LDX #<KSW ;Set offset from start of zero page to INPUT hook.

AND #$0F

IOPRT1 LDA #>COUT1 ;(Hi byte of the addr of KEYIN & COUT1 are equal.)

(B747) JMP DOSCOLD ;Jump into DOS's coldstart routine to build
------------ ;the DOS buffers and the page-three vector
. ;table and then run the "HELLO" program.
. ;*************** N O T E *****************
. ;* This instruction is a hacker's dream. *
. ;* For instance, you can change the jump *
. ;* to point to you own password or time- *
. ;* bomb routine that you have deviously *
. ;* embedded in an unused section of DOS. *
. ;*****************************************
* SEE dis'mbly titled *
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