Amiga ISO Collection/AmigaUtilCD2.iso/Misc/GXY-SYB.LHA/sybil/readme.txt

Text File | 1996-03-09 | 5.8 KB | 117 lines

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*            A T T E N T I O N   --  A T T E N T I O N          *
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First of all we at Utilities Unlimited wish to apologize for
the delay in the release of SYBIL.  Many reasons were involved
for the delay, the main reason being software.


Please take the time to fill out your warranty card.  This is the
ONLY way we know you have purchased SYBIL.  We sell SYBIL to
distributors and dealers throughout the world and we have no way
of telling who buys from them except via the warranty cards.


INSTALLATION INSTRUCTIONS:

The SYBIL hardware consist of TWO units.  The unit with the SWITCH
connects to the PARALLEL port.  The unit with the POT connects to
the VIDEO port.  When you are not using the unit, it is recommended
that the SWITCH be placed to the LEFT position, which disables the
SYBIL hardware (A1000 users-the SWITCH will be to the RIGHT, as your
unit installs backwards due to the parallel port being backwards on
your computer).  It *is* possible to plug the unit with the POT into
the parallel port....DON'T TRY IT...kiss your 8520 chips goodbye if
you do.

You may leave the SYBIL hardware installed at all times, however, if
you intend to use your printer, the switch must be in the "disable"
position.  Also, while using ANY SYBIL YOU MUST have your printer
either turned on or unplugged from the parallel port SYBIL unit...if
you do not, SYBIL will NOT work!


A word about MAC:

Well, it finally happened!  I pulled ALL of my hair out and got the
SYBIL to use MAC disks.  When I initially designed this product I
looked at a few MAC disks with the SYBIL hardware installed and was
able to determine that yes, we could read and write MAC format with
this hardware.  Hah!  Yes, the hardware would do it's job just fine,
and if MAC had a somewhat normal disk structure it would be as easy as
making a DOS copier for the Amiga.  Let me explain a little about MAC
format and why it is so difficult to use it on standard (non-drive
speed adjustable) disk drives:

The MAC 800K disk drive changes it's speed 5 times depending where the
heads are (upper and lower heads are always on the same track).  The
drive speed change from 390 to 594 RPMs.  The Amiga disk drives run at
300 RPMs.  So, as you can see, this is a dramatic difference from what
our (us Amigian's) equipment is normally capable of.  There are only
two ways to make a disk drive read and write MAC format.  1) Change the
speed of the drive motor (RPMs) or 2) Change the data rate at which a
disk's data is manipulated.  MAC disks are written with GCR (Group Code
Recording).  GCR normally has a 4us bit window, but since the MAC's
drive motor varies in speed, this also varies - from about 2.2us to
4.3us.  The PAULA chip in the Amiga can read and write 2us or 4us GCR,
but 2us is not really possible with the Amiga drives because they do
not spin fast enough and adjacent bits get wiped out.  Paula does,
however, have the ability to read a wide range.  In fact, Paula is able
to read the last 32 tracks of a MAC disk, and can actually write the
last 16.

A MAC disk is broken down into 5 "speed zones".  These zones change
every 16 tracks.  So, tracks 0-15 are all zone 1, 16-31 are all zone 2,
32-47 are all zone 3, 48-63 are all zone 4, and 64-79 are all zone 5.
The SYBIL hardware can read and write MAC format by slowing down PAULA
so that the 2us bit window can be adjusted over the necessary range.
This sounds rather complex, which it may be, but the principle is sound
and reliable.

MAC disk format is very odd.  Each sector is laid out in the following
fashion:  SYNC (FF's), Address Marker, SYNC (FF's), Data Marker, Sector
Tag, Data Block, Data Checksum, and EOS marker (End of Sector).  This
repeats for as many sectors that are found on the track.  Speaking of
which, as the heads get closer to the center of the disk, the number
of sectors per track get fewer.  On speed zone 1, you will find 12
sectors per track.  Every speed zone, the number of sectors per track
drops by 1.  So, on the last speed zone, there is 8 sectors. (12, 11,
10, 9, & 8)  Each sector is read/written one at a time.  Which means
that unlike the AmigaDos system (where whole tracks are read and
written in one revolution) many reads are required to get an entire
track's data.  This has no advantage to my knowledge.  It would be by
far faster to pull in an entire track and cache the sectors when needed
(which is something that I have been working on with the AMAX patch).
Basically to write new sector data, the header is found by reading all
of the headers on the track until the correct one is found (or times
out with an error condition) and then a small delay, then the data
block is written.  This process causes many "write splices".  That is
where the data gets shifted by a few bits making it nearly impossible
to read by dumping the whole track out and looking at it.

So, we (people who monkey around with MAC disks) are forced to read a
sector at a time and "piece" together a track.  That is why you will
notice that the POWER LED "blinks" to the beat of each sector when a
MAC disk is READ.  :-)

The patch to allow the actual READING/WRITING while using AMAX has been
changed again and will probably not be on this update disk.  It will
however be available thru our support BBS [phone] when
completely finished.  In the mean time, you can use the MAC2AMAX disk
converter to convert a MAC formatted disk into AMAX format.



Again, thank you for your patience!

Sincerely,

Jim Drew, Vice-President
          Utilities Unlimited of Oregon, Inc.
          Author/Designer of SYBIL