Changeset 816


Ignore:
Timestamp:
Jan 11, 2013, 8:26:18 PM (7 years ago)
Author:
pfusik
Message:

Sap.txt: replaced non-ASCII apostrophes.

File:
1 edited

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  • trunk/asma/Docs/Sap.txt

    r469 r816  
    2020The SAP format contains the original data and code used to playback the Atari music. SAP players actually run the program contained in the SAP file on an emulated or real (sapemu) 6502 processor. The program controls the POKEY chip, which generates the sound.
    2121Identical method is used with platforms other than Atari, for example the SID format for the C64 music.
    22 Important advantages of SAP over, let’s say, MP3, are that SAP files are very small (about 5 KB on average) and play more accurately as new players improve their emulation. The downside is that SAP files are generally hard to create. Creating SAP files from Atari software is called ripping and requires knowledge of the 6502 assembly language. On the other hand, Atari music in popular formats such as CMC or RMT can be easily converted to SAP (and back) using ASAP.
     22Important advantages of SAP over, let's say, MP3, are that SAP files are very small (about 5 KB on average) and play more accurately as new players improve their emulation. The downside is that SAP files are generally hard to create. Creating SAP files from Atari software is called ripping and requires knowledge of the 6502 assembly language. On the other hand, Atari music in popular formats such as CMC or RMT can be easily converted to SAP (and back) using ASAP.
    2323One SAP file may contain multiple independent tunes - these are called "subsongs". For example, several songs from one game may be ripped into one SAP file. Over 90% SAP files contain just one song. Unfortunately many audio players do not support the concept of multiple subsongs per file.
    2424
     
    103103
    104104FASTPLAY
    105     Number of scanlines between calls of the player routine. A scanline is defined to be 114 Atari clock cycles. FASTPLAY defaults to one frame: 312 scanlines for PAL (about 50 Hz), 262 for NTSC (about 60 Hz). Most songs don’t include this tag. Common values are 156 (twice per frame), 104 (three times per frame) and 78 (four times per frame). ASAP 3.0.0 and above supports FASTPLAY up to 32767. Other SAP players may limit the value to 312.
     105    Number of scanlines between calls of the player routine. A scanline is defined to be 114 Atari clock cycles. FASTPLAY defaults to one frame: 312 scanlines for PAL (about 50 Hz), 262 for NTSC (about 60 Hz). Most songs don't include this tag. Common values are 156 (twice per frame), 104 (three times per frame) and 78 (four times per frame). ASAP 3.0.0 and above supports FASTPLAY up to 32767. Other SAP players may limit the value to 312.
    106106
    107107INIT
     
    157157    D600-D6FF - COVOX chip if enabled via the COVOX tag (ASAP only). The COVOX consists of four unsigned 8-bit DACs: 0 and 3 for the left channel, 1 and 2 for the right channel.
    158158    D700-D7FF - reserved for expansions, do not use.
    159     D800-FFFF - RAM. FFFE/FFFF is 6502’s interrupt vector for POKEY timer interrupts.
     159    D800-FFFF - RAM. FFFE/FFFF is 6502's interrupt vector for POKEY timer interrupts.
    160160
    161161Timing: The main clock is 1773447 Hz (PAL) or 1789772.5 Hz (NTSC). There are 114 cycles per scanline, including 9 cycles memory refresh not available for the 6502 - same as in the Atari with ANTIC DMA disabled completely. WSYNC and VCOUNT registers may be used for delays. Note that some SAP players reset VCOUNT at the FASTPLAY rate instead of every frame.
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