[Simh] SimH: Bugfix in VAX/PDP11 TK50 driver ... more facts

[Jörg Hoppe]

>  ------------------------------

>  One hates to spoil a beautiful theory with an ugly fact, but here's a
>  direct quote from the Tape MSCP Specification, Rev 2.02, dated November
>  8, 1987:
>
>  Still, the driver could be "right" because, as Tim noted, TMSCP went
>  through a lot of variants and implementation missteps.  The TK50 may
>  have done object counting differently (and incorrectly).  I don't have a
>  TK50 manual that details its implementation of TMSCP (DEC guarded that
>  very carefully), and the TMSCP spec only has a revision history back to
>  v1.6.  The revision history
>  does mention a bunch of TK50 "temporary waivers," as well as five
>   ones, so it's certainly possible that the TK50
>   doing things wrong at the time this version of Ultrix was released.
>
>   would be useful  to try installing a later version of Ultrix from the
>  TK50 and see what happens.
>
>  I've sent the MSCP and TMSCP specs to be posted on Bitsaver.
>  /Bob

Thanks for that TMSCP doc!

I spent the day testing some combinations of SimH/tape image/Ultrix version.
- SimH: original V3.8-1 vs. my "JH-path" version
- Ultrix installation: v3.0 vs. v4.0
- Test tapes:
         TAPE1 =   www.bitsavers.org/bits/DEC/vax/ultrix/3.0/Ultrix-32_3.0_unsupp.tap
         TAPE2 =  "DEC C FOR RISC-ULTRIX TK50 (DEC 1991, AQ-PCXFA-BE ME214414).simh_tq.tk50" (own copy, call me)

Results:
1) A real uVAX under Ultrix 3.0 can read the real "Ultrix-32_3.0_unsupp.tap" (surprise!)
    The controller was QBUS TQK50 (M7546), the drive was TK50.
2) SimH can not read  "Ultrix-32_3.0_unsupp.tap" error free, neither on Ultrix v3 nor on Ultrix v4.
3) The TMSCP driver in Ultrix v4 is apparently different from v3:
    The error patterns under SimH are similar, but not the same. Data loss is greater under v4.
4) My little hack (I was so proud of it:-)) is very weak:
    - Sure, it makes "Ultrix-32_3.0_unsupp.tap" readable under Ultrix v3, as intended.
    - But SimH can not ">>>  boot MUA0" anymore.
    - It does not work on Ultrix v4 with "Ultrix-32_3.0_unsupp.tap"
    - It does not work with other tapes under Ultrix v3: Tapes with a small file before EOT fail.

I attached my test setups&  protocols, if somebody likes to work with it.

How would we continue from here?

regards,
Joerg





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