Prism Leisure Protection - Revision history

Enigma at 09:26, 10 October 2026

2026-10-10T09:26:33Z

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	** '''Recording direction.''' In a double-sided KryoFlux capture, head 1 reads the back side in reverse time order. This applies to the signature track as well as to tracks 1–35. Read without reversal, the <code>$AC</code> pattern looks like 3-1-2-2 instead of 2-2-1-3.		** '''Recording direction.''' In a double-sided KryoFlux capture, head 1 reads the back side in reverse time order. This applies to the signature track as well as to tracks 1–35. Read without reversal, the <code>$AC</code> pattern looks like 3-1-2-2 instead of 2-2-1-3.
	** '''Signal distortion.''' The signature track signal on back sides can be heavily peak-shifted. On [[Power-Pack]] source 7, Disk 1 back side, the measured intervals were 1.30 / 1.88 / 2.18 / 2.60 cells instead of 1 / 2 / 2 / 3. It then decodes cleanly only at exactly 3.50 µs per cell.		** '''Signal distortion.''' The signature track signal on back sides can be heavily peak-shifted. On [[Power-Pack]] source 7, Disk 1 back side, the measured intervals were 1.30 / 1.88 / 2.18 / 2.60 cells instead of 1 / 2 / 2 / 3. It then decodes cleanly only at exactly 3.50 µs per cell.

	~~== Verification ==~~

	~~All sources tagged with this protection were checked in VICE with true drive~~
	~~emulation (65 G64 images of 28 pages):~~

	* 61 images pass the check.
	* 1 image passes only sometimes, depending on the start timing: [[Football Manager 2]] source 2 "(!)".
	* 3 disk sides never run the check: the back sides of [[Karnov]] and [[Predator]] (the Predator back side carries an <code>$AC</code> track 41 that is never read), and [[Fun Collection Vol.1]] disk 5, whose directory shows the signature but which is not checked.

	==== Pages that refer to this protection ====		==== Pages that refer to this protection ====

	{{Special:Whatlinkshere/Prism Leisure Protection}}		{{Special:Whatlinkshere/Prism Leisure Protection}}

Enigma at 09:24, 10 October 2026

2026-10-10T09:24:22Z

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Enigma at 05:11, 10 October 2026

2026-10-10T05:11:22Z

← Older revision		Revision as of 05:11, 10 October 2026
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	</pre>		</pre>

	* '''Upload (<code>$C003</code>):''' the drive code is stored in C64 memory		* '''Upload (<code>$C003</code>):''' the drive code is stored in C64 memory at <code>$C100</code>–<code>$C1FF</code>, XOR-encrypted with <code>$05</code>. That's the high byte of its drive address, which the upload loop uses as the key. It is sent with <code>M-W</code> in 32-byte chunks to drive <code>$0500</code>–<code>$05FF</code> and decrypted on the fly.
	at <code>$C100</code>–<code>$C1FF</code>, XOR-encrypted with		* '''Read-back (<code>$C070</code>):''' the C64 opens the command channel, sends <code>M-R</code> <code>$FF $05</code>, and stores the single byte it gets back at <code>$C0FF</code>.
	<code>$05</code>. That's the high byte of its drive address, which the		* '''Decision:''' if the byte is not <code>$C2</code>, the loader jumps through the reset vector, and the machine restarts. This is the reset seen when the check fails.
	upload loop uses as the key. It is sent with <code>M-W</code> in 32-byte
	chunks to drive <code>$0500</code>–<code>$05FF</code> and decrypted on the
	fly.
	* '''Read-back (<code>$C070</code>):''' the C64 opens the command channel,
	sends <code>M-R</code> <code>$FF $05</code>, and stores the single byte it
	gets back at <code>$C0FF</code>.
	* '''Decision:''' if the byte is not <code>$C2</code>, the loader jumps
	through the reset vector, and the machine restarts. This is the reset seen
	when the check fails.

	The result byte is used three times, so patching only the		The result byte is used three times, so patching only the
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	# as the comparison value at <code>$C0F5</code>;		# as the comparison value at <code>$C0F5</code>;
	# as the high byte of the jump target. <code>$C0FF</code> is also the		# as the high byte of the jump target. <code>$C0FF</code> is also the operand of <code>JMP $xx00</code> at <code>$C0FD</code>, so only the correct value <code>$C2</code> continues at <code>$C200</code>;
	operand of <code>JMP $xx00</code> at <code>$C0FD</code>, so only the		# as the decryption key. The code at <code>$C200</code> XORs page <code>$C300</code> with <code>$C0FF</code> and then jumps to <code>$C300</code>:
	correct value <code>$C2</code> continues at <code>$C200</code>;
	# as the decryption key. The code at <code>$C200</code> XORs page
	<code>$C300</code> with <code>$C0FF</code> and then jumps to
	<code>$C300</code>:

	<pre>		<pre>

Enigma at 05:09, 10 October 2026

2026-10-10T05:09:35Z

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	== The signature track ==		== The signature track ==

	* Track 41 has no sectors, headers or checksums. It contains the byte		* Track 41 has no sectors, headers or checksums. It contains the byte <code>$AC</code> repeated about 7,140 times per revolution.
	<code>$AC</code> repeated about 7,140 times per revolution.		* In GCR bits <code>$AC</code> is <code>10101100</code>. On the disk this appears as a repeating flux interval pattern of 2-2-1-3 bit cells.
	* In GCR bits <code>$AC</code> is <code>10101100</code>. On the disk this		* The track is written at the bit rate of speed zone 2 (3.50 µs per cell). This is not the zone the 1541 DOS would use for track 41.
	appears as a repeating flux interval pattern of 2-2-1-3 bit cells.		* No sync mark was found in the flux of any analyzed disk. The pattern simply runs once around the track.
	* The track is written at the bit rate of speed zone 2 (3.50 µs per
	cell). This is not the zone the 1541 DOS would use for track 41.
	* No sync mark was found in the flux of any analyzed disk. The pattern
	simply runs once around the track.

	<pre>		<pre>
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	In short:		In short:

	* The drive reads raw bytes from track 41 without looking for a sync or a		* The drive reads raw bytes from track 41 without looking for a sync or a header.
	header.		* It searches up to 255 × 256 bytes (about nine revolutions) for an <code>$AC</code>.
	* It searches up to 255 × 256 bytes (about nine revolutions) for an
	<code>$AC</code>.
	* After that, 256 bytes in a row must be <code>$AC</code>.		* After that, 256 bytes in a row must be <code>$AC</code>.
	* The result goes to drive address <code>$05FF</code>: <code>$C2</code>		* The result goes to drive address <code>$05FF</code>: <code>$C2</code> means passed, <code>$00</code> means failed.
	means passed, <code>$00</code> means failed.
	* A second job returns the head to track 18.		* A second job returns the head to track 18.

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	* A 35-track copy or a D64 image loses track 41, and the check fails.		* A 35-track copy or a D64 image loses track 41, and the check fails.
	* A track 41 that decodes as "almost <code>$AC</code>" fails too. The check		* A track 41 that decodes as "almost <code>$AC</code>" fails too. The check needs 256 correct bytes in a row, so a single shifted or lost bit in every few bytes is enough to break it.
	needs 256 correct bytes in a row, so a single shifted or lost bit in every
	few bytes is enough to break it.
	* '''Back sides (flippy sides) need care when imaging:'''		* '''Back sides (flippy sides) need care when imaging:'''
	** '''Recording direction.''' In a double-sided KryoFlux capture, head 1		** '''Recording direction.''' In a double-sided KryoFlux capture, head 1 reads the back side in reverse time order. This applies to track 41 as well as to tracks 1–35. Read without reversal, the <code>$AC</code> pattern looks like 3-1-2-2 instead of 2-2-1-3.
	reads the back side in reverse time order. This applies to track 41 as		** '''Signal distortion.''' The track 41 signal on back sides can be heavily peak-shifted. On ''Power-Pack'' source 7, Disk 1 back side, the measured intervals were 1.30 / 1.88 / 2.18 / 2.60 cells instead of 1 / 2 / 2 / 3. It then decodes cleanly only at exactly 3.50 µs per cell.
	well as to tracks 1–35. Read without reversal, the <code>$AC</code>
	pattern looks like 3-1-2-2 instead of 2-2-1-3.
	** '''Signal distortion.''' The track 41 signal on back sides can be heavily
	peak-shifted. On ''Power-Pack'' source 7, Disk 1 back side, the measured
	intervals were 1.30 / 1.88 / 2.18 / 2.60 cells instead of 1 / 2 / 2 / 3.
	It then decodes cleanly only at exactly 3.50 µs per cell.

	== See also ==		== See also ==

Enigma at 05:08, 10 October 2026

2026-10-10T05:08:22Z

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	around the whole track. A disk copied with a normal 35-track copier lacks		around the whole track. A disk copied with a normal 35-track copier lacks
	this track, and the check fails.		this track, and the check fails.

	~~The description below is based on ''Power-Pack'' (Rushware, 1987): a trace~~
	~~of the check under VICE with true drive emulation, analysis of the KryoFlux~~
	~~streams of sources 4, 5 and 7, and a VICE test of the repaired images.~~

	Disk title in directory is modified to show in green color.		Disk title in directory is modified to show in green color.

Enigma at 05:08, 10 October 2026

2026-10-10T05:08:00Z

Show changes

Enigma at 06:24, 23 March 2024

2024-03-23T06:24:09Z

← Older revision		Revision as of 06:24, 23 March 2024
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	Disk title in directory is modified to show in green color.		Disk title in directory is modified to show in green color.

	Used by Electric Dreams, Software Studios, ~~Image Works~~, Thalamus		Used by Electric Dreams, Software Studios, Mirrorsoft Ltd., Thalamus

	==== Pages that refer to this protection ====		==== Pages that refer to this protection ====

	{{Special:Whatlinkshere/Prism Leisure Protection}}		{{Special:Whatlinkshere/Prism Leisure Protection}}

Enigma at 06:22, 23 March 2024

2024-03-23T06:22:57Z

← Older revision		Revision as of 06:22, 23 March 2024
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	Disk title in directory is modified to show in green color.		Disk title in directory is modified to show in green color.

	Used by Electric Dreams, Software Studios		Used by Electric Dreams, Software Studios, Image Works, Thalamus

	==== Pages that refer to this protection ====		==== Pages that refer to this protection ====

	{{Special:Whatlinkshere/Prism Leisure Protection}}		{{Special:Whatlinkshere/Prism Leisure Protection}}

Enigma at 06:21, 23 March 2024

2024-03-23T06:21:39Z

← Older revision		Revision as of 06:21, 23 March 2024
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	Disk title in directory is modified to show in green color.		Disk title in directory is modified to show in green color.

			Used by Electric Dreams, Software Studios

	==== Pages that refer to this protection ====		==== Pages that refer to this protection ====

	{{Special:Whatlinkshere/Prism Leisure Protection}}		{{Special:Whatlinkshere/Prism Leisure Protection}}

Enigma at 06:18, 23 March 2024

2024-03-23T06:18:15Z

← Older revision		Revision as of 06:18, 23 March 2024
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	Checks data duplication on track 41.		Checks data duplication on track 41. ($AC signature)

	Disk title in directory is modified to show in green color.		Disk title in directory is modified to show in green color.