[Simh] 8" Floppy disk image getting HALT error

Tue Jul 11 18:02:29 EDT 2017

On 2017-07-11 21:09, Timothe Litt wrote:
> VMS mount /over=id /foreign is the quickest way to identify files-11 and
> RT disks.  FILES-11 can be read directly; use EXCHANGE for RT-11.  Once
> you have the disk mounted on VMS, you can network it to wherever you like.

Similar story if you have RSX. I might have forgotten a thing or two 
about VMS here, but I would have thought /OVER=ID/FOREIGN would not then 
let you access the disk in the direct way if it is Files-11.

> If you insist on doing things the hard way, there is low-level detail to
> worry about.
>
> The first  track on DEC 8" floppies is reserved for boot (but not used)
> in the standard RX01/2 formats.  It's not used by any DEC OS.  Not even
> for booting (the DEC boot block is the first LBN following the reserved
> track.)
>
> Both are 77 tracks, 1 sided, 26 sectors/track.  The rx01 is 128
> bytes/sector; the rx02 256.  So an RX01 image will be about 251KB, an
> RX02 about 501KB.

Which then makes sense for data to start at track 26.

> Logical blocks are 512 bytes; meaning that an LBN consists of 4 or 2
> physical sectors.  The physical sectors are interleaved.  If you have a
> physical dump of the disk (and your tools haven't outsmarted you), the
> easiest thing to do is to de-interleave it.
>
> Use the attached utility, which documents the format & will
> interleave/deinterleave a floppy image using the usual interleave rules.
>
> 19D0(16) is close to 26 * 256 (short by 48 bytes), so I'd guess you have
> an rx02 and are seeing the empty boot track.  (Although not guaranteed,
> the track was usually written with all zeroes).

I think Walked was a little careless in his conversion. He said bytes 
0-6655, which actually turns out to be 01A0, or exactly where track 1 
starts.

> The 48 bytes may be left over from formatting, or an artifact of how
> you're reading the medium.  Or an indication that your recovery dropped
> something.  Hopefully it checks the CRCs..

Or just a conversion error. :-)

> The E5 is probably left over from formatting.  I think it was part of
> the sync pattern, and that the formatter wrote
>
> If you see 8-bit data, it's probably RT11 or Files-11.  These are
> self-identifying - block 1 (the second block) will have a filesystem
> name in starting at byte 760(8).  Will be DECFILE11A for ODS1 or
> DECFILE11B for ODS2, DECRT11A for RT11.  RSTS is also possible - I don't
> remember it's code, probably DECRSTS11A.  Given that, data
> (deinterleaved), humans can easily tell what you have.

Unfortunately it's not that easy.
Files-11 do indeed have that identifier in block 1. RT-11 however, might 
not. There is no requirement and no checking, and depending on what 
version, and what tool, you might be lucky and find such a string there, 
but the absence don't mean anything.
VMS Exchange helpfully enough actually writes "DECVMSEXCHNG" there. 
(cut-and-pasted from a dump right here and now)
FLX (under RSX) do not write anything at all when you initialize the 
disk with an RT-11 file structure.

I don't have any RSTS/E disk images to quickly peek into.

But with some detective work, you can still figure out if it is an RT-11 
volume.

But the fact that the dump seem to get directly to document data without 
anything at all suggest that there isn't any file structure at all on 
the disk.

> RT11 files are contiguous, so recovery is easy.  FILES-11 files can be,
> but probably aren't.  You have to read mapping pointers.  There are
> tools that will do that (one of these daze I do intend to release mine.)
>
> But it's much easier to just run EXCHANGE and say "COPY" by filename :-)

Indeed. Seems unneccesary work to write a tool to parse that out when 
tools already exist. You can do it in VMS, or RSX, RSTS/E or Ultrix, 
without having to write any code.

> As for WPS-8  - yes, it's packed into 12 bits - but it's also encoded (I
> vaguely remember it as a 6-bit code with shift & formatting - but I'd
> have to look up the code I wrote to translate it.)  In any case, it
> would not look like text to a "modern" filesystem.

Yeah. I think we can exclude WPS from likely formats.

	Johnny

>
> Have fun.
>
> On 11-Jul-17 13:26, Walker Sampson wrote:
>> Hi everyone,
>>
>> Many thanks for this feedback. A fair amount to chew on here. I’ve sent a request to the donor to share the disk image, if I get a positive I’ll be happy to throw up a Dropbox link to it for others to examine.
>>
>> This may mean a problematic read of the disk itself, but addresses 00000 – 019D0 are all zeroed out, or about bytes 0 – 6655.
>>
>> Data begins at byte 6657, and that is the document I mentioned. Last byte of the document is 73080 and then just blocks of either zero or E5E5E5E5 till the end of the disk.
>>
>> To Paul’s point of mounting a RK05 drive – which drive should I be mounting here, assuming it is the RX02 disk it seems to be? “AT RX01 <disk_image>” still gets a HALT error. Of course, as you all point out, perhaps this isn’t a bootable disk, period. “SH RX01” gives “RX1, 256KB, attached to test-decrx01.img, write enabled”
>>
>> FYI as well, on a modern HFS+ system, the disk image file is coming in at 256 KB.
>>
>> Any thoughts on the run of zeroes and E5E5E5E5?
>>
>> Thanks again,
>>
>> Walker
>>
>>  On 7/11/17, 6:29 AM, "Simh on behalf of Johnny Billquist" <simh-bounces at trailing-edge.com on behalf of bqt at softjar.se> wrote:
>>
>>     Hi.
>>
>>     On 2017-07-10 22:10, Walker Sampson wrote:
>>     > Hi everyone,
>>     >
>>     > Let me preface this by saying that I’m unfamiliar with the original PDP
>>     > machines. I work as a digital archivist and have received 8” floppy
>>     > disks from which I need to recover data.
>>     >
>>     > I believe I have recovered at least partial data from these disks; I’ve
>>     > connected a Y-E Data 8” floppy drive to a KryoFlux floppy disk
>>     > controller and gotten positive sector results setting the format to a
>>     > DEC RX02 sector image. When I investigate the resulting disk image in a
>>     > hex editor, I am seeing clearly a report document, so I don’t believe I
>>     > have a false positive.
>>     >
>>     > Outside of observing in a hex editor however, I don’t know how to access
>>     > the disk or its contents. Using SIMH, I haven’t gotten the virtual
>>     > machine to boot the floppy disk image.
>>     >
>>     > Commands “AT RK01 <disk_image>” and then “BOOT RK01” give me a “HALT
>>     > instruction, PC: 000002 (HALT)” message for the PDP-11 program. The
>>     > PDP-8 stalls indefinitely and the PDP-10 outputs “Non-existent device”
>>     > as well.
>>     >
>>     > I can’t go back to the donors and ask what machines these 8” floppies
>>     > were used with, so I’m not sure how to begin troubleshooting.
>>     >
>>     > Any advice in that area is much appreciated!
>>     >
>>     > Thanks,
>>     >
>>     >
>>     > Walker
>>
>>     To sum things up. You can probably ignore all the questions about if
>>     this really is some DEC floppy, what kind of format it has, and so on.
>>     If kryoflux managed to extract data that looks valid with RX02 parameter
>>     settings, then I'd say we can be sure it is an RX02 disk. And this
>>     format was unique to DEC, so it can't be anything else.
>>
>>     Which also means, you already have managed to exact all the bits, and
>>     most probably correct. The next question is just about restoring the
>>     data in a more coherent form, which means getting it in the form of
>>     files, and understanding the format of the files.
>>
>>     For this, we need to know what system the floppy was written on. Paul
>>     Koning gave the most useful advice. The first few blocks will usually be
>>     enough to find out what system the floppy was written on.
>>
>>     RX02 floppies could certainly be bootable, but most are not. OS/8 (and
>>     derivatives) for the PDP-8, and RT-11 for the PDP-11 were the ones that
>>     supported RX02 as a bootable system. Other systems supported the
>>     floppes, but only as a way of carrying bits around, so not being able to
>>     boot from the floppy is probably to be expected.
>>
>>     So, if you could give us just the first few blocks, it should be
>>     possible to tell what file system it has, and that gives us OS, file
>>     structure and probably the ability to work out the rest in quick order.
>>
>>     	Johnny
>>
>>     --
>>     Johnny Billquist                  || "I'm on a bus
>>                                        ||  on a psychedelic trip
>>     email: bqt at softjar.se             ||  Reading murder books
>>     pdp is alive!                     ||  tryin' to stay hip" - B. Idol
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-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol