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Atari 8-bit Software Preservation Initiative


Farb

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okay... what's the IP I perma banned people who sat a zero for more that 48 hours

 

still got nothing coming

 

I will manually add the peer ip and port I leach at 330MiB down and feed at 25 MiB up

Edited by _The Doctor__
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it is rolling along but rather slowly.... only 300 KiB/s I sure hope everyone delete all parts and files of the failed torrents as the name and folders may resend whatever was part of the old torrent

 

2 seeds found

 

I am currently uploading 3x more than I am getting...

Edited by _The Doctor__
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Here is a clean working dump of Zeppelin. As the name of the file implies, this title works only on an 810 drive. It will randomly fail on a 1050 and probably on everything else as well. So if using Altirra, make sure the drive is configured as 810. Will elaborate later ...

 

I wanted to make a detailed article about this because it is quite interesting. But never found the time. So I am posting here the main concept "as headlines" without much of a redaction. Technically oriented people will probably understand, I hope :)

 

- Zeppelin uses the so called skew align as one of its protections.

- Skew align refers to a specific angular alignment of the sectors across different tracks.

- Most titles with this protection were formatted aligned with the index hole.

- So that the same physical sector number is located at almost the same angular position in all the tracks.

- The typical protection check performs something like reading physical sector one of a track, then sector one of an adjacent track, and measures the total time taken. It should be one full revolution.

- Some protections measure the actual RPM before, others assume a nominal value.

- The specific drive and firmware timings, such as seek time and settle delay, are not relevant. It always takes one full revolution because the revolution time is much bigger.

- The total time since the drive starts reading the first sector until being ready to read the other one in the adjacent track is in the order of 150 ms; while a full revolution takes 208 ms.

- So the drive always needs to wait one full revolution disregarding if it was ready 20 ms earlier or later.

 

- Zeppelin disks are is not aligned to the index hole. The skew align was achieved likely using timing.

- That means that sectors with the same physical number in different tracks are not at the same angular position.

- It also makes the formatted alignment not that accurate because it is more influenced by the drive RPM.

- The angular distance between specific sectors on adjacent tracks is not constant. This is probably on purpose to make reproduction of the alignment more difficult.

- But note that yet the alignment across multiple copies is, of course, (more or less) constant for a given pair of tracks.

- Protection is checked similarly as the typical case, measuring the elapsed time since reading physical sector one of a random track, until reading also physical sector one on an adjacent track.

- But because of the not constant alignment, it doesn’t always take one revolution. The software has a table for the expected time for each track.

- And because now in some tracks it takes less time than one revolution, the internal drive timings become relevant and significant.

- The protection assumes the timing matches a standard 810 drive. Just about any other drive would randomly fail the protection.

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- But because of the not constant alignment, it doesn’t always take one revolution. The software has a table for the expected time for each track.

 

Slight correction: It's actually two tables to diffenrentiate between PAL and NTSC.

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