Subject: Re: function of the atr-file header
Date: 23 Sep 1996 22:32:20 GMT
From: feb6399@osfmail.isc.rit.edu (Frank Barrus)
Organization: Rochester Institute of Technology, Rochester, NY
Newsgroups: comp.sys.atari.8bit
References: <324433D6.1E78@kawo2.rwth-aachen.de>

In article <324433D6.1E78@kawo2.rwth-aachen.de>,
Matthias Belitz  <matz@kawo2.rwth-aachen.de> wrote:
>Hello !
>
>Is anyone here, could tell me the function of the 16 byte file-header of
>the ATR-files.
>
>Thanks  Matt

Well, here's the structure from it, taken out of ACE
(the Atari Computer Emulator)

struct sio2pc_image_hdr {
        byte    code_lo, code_hi;       /* ID code = 0x0296 */
        byte    size_b1, size_b2;       /* low 16-bits of size */
        byte    secsize_lo, secsize_hi; /* sectors size: 128/256 */
        byte    size_b3, size_b4;       /* high 16-bits of size (paragraphs) */
        byte    resv[6];                /* reserved */
        byte    numerr_hi, numerr_lo;   /* number of sectors with errors */
};

struct errormap {
        byte    sec_lo, sec_hi;         /* sector with error */
        byte    cstat;                  /* communication status */
        byte    hstat;                  /* hardware status */
        byte    resv[4];                /* reserved */
};

Note that the size (which is stored in size_b1 through size_b4)
is in paragraphs, or multiples of 16.  Thus, take the total number
of sectors, multiply by the sector size, and divide by 16, then store
this result across those four bytes.
(Actually, I might have added bytes 3 and 4 to it.... or someone
else might have already.  I can't remember now)

Note that the errormap was an extension I added, but I'd like
to see it get standardized, since they're useful for some disks.

Basically, the errormap sits at the end of the data, and 'numerr'
specifies the number of error records.  Each one tells what
sector should give an error when reading it, along with the
codes that should be given for the error.  The reserved part
could be used to add other information for really strange
errors.  (but make sure you publish the extensions, if you
add any!)

I hope this helps some.

        - Frank

--
Frank "Shaggy" Barrus: feb6399@osfmail.isc.rit.edu, shaggy@csh.rit.edu
http://www.csh.rit.edu/~shaggy