Atari Floppy Disk Copy Protection By Jean Louis-Guérin (DrCoolZic) Revision 1.4 – June 24, 2015 Atari Floppy Disk Copy Protection Table of Contents Table of Contents ................................................................................................................ 2 Chapter 1. Presentation ................................................................................................... 4 Chapter 2. Copy protections detail description ............................................................. 5 2.1 Protections based on data .................................................................................................... 5 2.1.1 Number of tracks (NOT) ........................................................................................................... 6 2.1.2 Shifted tracks (SFT) ................................................................................................................. 7 2.1.3 Track Layout Pattern (TLP) ...................................................................................................... 9 2.1.4 Number of Sectors (NOS) ........................................................................................................ 9 2.1.5 Sector Sizes (SSZ) ................................................................................................................. 10 2.1.6 Invalid ID Field (IIF) ................................................................................................................ 10 2.1.7 Duplicate Sector Number (DSN) ............................................................................................ 12 2.1.8 Sector within sector (SWS) .................................................................................................... 13 2.1.9 Non Standard DAM (NSD) ..................................................................................................... 13 2.1.10 Sector with No ID (SNI) .......................................................................................................... 14 2.1.11 Sector with No Data (SND) .................................................................................................... 14 2.1.12 Data CRC Error (DCE) ........................................................................................................... 14 2.1.13 Data Track (DTT) ................................................................................................................... 15 2.1.14 Hidden Data into GAP (HDG) ................................................................................................ 15 2.1.15 Hidden data into nonstandard tracks (HDT) .......................................................................... 15 2.1.16 Invalid Data in Gap (IDG) ....................................................................................................... 16 2.1.17 Invalid Sync-mark Sequence (ISS) ........................................................................................ 16 2.1.18 Partially formatted track (PUT) ............................................................................................... 16 2.1.19 Fuzzy Sector (FZS) ................................................................................................................ 17 2.1.20 Fuzzy Track (FZT) .................................................................................................................. 17 2.2 Protections based on timing ............................................................................................... 18 2.2.1 Long / Short Sector (LGS & SHS) .......................................................................................... 18 2.2.2 Long/Short Track (LGT & SHT) ............................................................................................. 19 2.2.3 Sector Bit-rate Variation (SBV) .............................................................................................. 19 2.2.4 No Flux Area (NFA) ................................................................................................................ 20 Chapter 3. Preservation of Atari floppy disks ...............................................................21 3.1 Cleaning a floppy disk to create correct image ................................................................ 21 3.2 Why do we need several revolutions for preservation? .................................................. 21 3.3 Kryoflux short presentation ................................................................................................ 23 3.4 Supercard Pro short presentation ...................................................................................... 23 Chapter 4. Technical Information ...................................................................................24 4.1 Atari Low-Level Formats ..................................................................................................... 24 4.1.1 Format for 9/10/11 Sectors of 512 Bytes ............................................................................... 25 4.1.2 “Standard” 128-256-512-1024 Bytes / Sector Format ........................................................... 26 4.2 WD1772 DPLL Input Circuitry ............................................................................................. 27 4.2.1 Description ............................................................................................................................. 27 4.2.2 WD1772 Detection of Fuzzy Border Bits ............................................................................... 29 4.3 WD1772 MFM track language ............................................................................................. 30 4.4 WD1772 Synchronization (sync marks detection) ............................................................ 31 4.5 False sync mark detection .................................................................................................. 32 4.6 Overlapping Sync Mark ....................................................................................................... 32 4.6.1 Overlapping $4489-$4489 ($A1-$A1) .................................................................................... 32 4.6.2 Overlapping $5224-$4489 ($C2-$A1) .................................................................................... 33 4.6.3 Overlapping $4489-$5224 ($A1-$C2) .................................................................................... 33 4.6.4 Overlapping $5224-$5224 ($C2-$C2) .................................................................................... 33 4.6.5 Invalid Sync sequence ........................................................................................................... 33 4.7 WD1772 Bug in Read/Write Track commands .................................................................. 34 4.8 WD1772 CRC Information.................................................................................................... 35 4.8.1 CRC Computation .................................................................................................................. 35 4.8.2 Playing with the CRC ............................................................................................................. 35 4.9 No Flux Area on Disk ........................................................................................................... 37 4.9.1 Checking NFA with the WD1772 ........................................................................................... 37 Copyleft Jean Louis-Guérin (DrCoolZic) – Rev 1.4 - June 24, 2015 Page 2 / 77 Atari Floppy Disk Copy Protection 4.9.2 Special case of No Flux Area over index ............................................................................... 38 4.10 Unformatted Diskette / Track / Sector ................................................................................ 41 4.10.1 Presentation ........................................................................................................................... 41 4.10.2 Partially unformatted track ..................................................................................................... 42 4.10.3 Partially formatted Track ........................................................................................................ 44 4.10.4 Unformatted track detection ................................................................................................... 44 4.10.5 How to reproduce unformatted areas on Floppy Disks? ........................................................ 44 4.11 Fuzzy Bits ............................................................................................................................. 46 4.11.1 Flux Reversals in Ambiguous Area ........................................................................................ 46 4.11.2 MFM Flux Timing Violation..................................................................................................... 46 4.11.3 Weak Bit ................................................................................................................................. 47 4.12 Write Splices ......................................................................................................................... 48 4.12.1 Sector write splices ................................................................................................................ 48 4.12.2 Track write splices .................................................................................................................. 49 4.13 Hidden data