From: will.senn@gmail.com (Will Senn)
Subject: [TUHS] Determining what was on a tape back in the day
Date: Mon, 20 Nov 2017 11:37:34 -0600 [thread overview]
Message-ID: <fb0ad671-8b65-cd37-bb4c-6fceab8568d0@gmail.com> (raw)
In-Reply-To: <20171120160148.EED1818C091@mercury.lcs.mit.edu>
On 11/20/17 10:01 AM, Noel Chiappa wrote:
> > The 0th block does seem to contain some PDP-11 binary - a bootstrap of
> > some sort. I'll look in more detail in a bit.
>
> OK, I had a quick look, and it seems to be a modified version of mboot.s:
>
> http://minnie.tuhs.org/cgi-bin/utree.pl?file=V6/usr/source/mdec/mboot.s
>
> I had a look through the rest of the likely files in 'mdec', and I didn't find
> a better match. I'm too lazy busy to do a complete dis-assembly, and work out
> exactly how it's different, though..
>
>
> A few observations:
>
> 000: 000407 000606 000000 000000 000000 000000 000000 000001
>
> An a.out header, with the 0407 'magic' here performing its original intended
> function - to branch past the header.
>
> 314: 105737 177560 002375
>
> Some console I/O stuff - this two instruction loop waits for the input
> ready bit to be set.
>
> 326: 042700 177600 020027 000101 103405 020027 000132 101002
>
> More character processing - the first instruction clears the high bits of R0,
> and the next two sets of two instructions compare the contents with two
> characters (0101 and 0132), and branch.
>
> 444: 000207 005000 021027 000407 001004 016020
> 460: 000020 020006 103774 012746 137000 005007
>
> This seems like the code that checks to see if the thing is an a.out file
> (note the 'cmp *r0, $0407'), but the code is different from that code in
> mboot.s; in that, the instruction before the 'clr r0' (at 0446 here) is a
> 'jsr', whereas in this it's an 'rts pc'. And the code after the 'cmp r0, sp'
> and branch is different too. I love the '05007' - not very often you see
> _that_ instruction!
>
> 502: 012700 177350 012701 177342 012711 000003 105711
>
> Clearly the code at 'taper:' (TC11 version).
>
> Noel
Thanks for the insight into how to look into this. I'm off to refreshing
my pdp-11 assembly language skills...
Will
--
GPG Fingerprint: 68F4 B3BD 1730 555A 4462 7D45 3EAA 5B6D A982 BAAF
next prev parent reply other threads:[~2017-11-20 17:37 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-20 16:01 Noel Chiappa
2017-11-20 17:37 ` Will Senn [this message]
-- strict thread matches above, loose matches on Subject: below --
2017-11-20 19:42 Noel Chiappa
2017-11-20 17:00 Noel Chiappa
2017-11-19 20:46 Steve Simon
2017-11-19 18:45 Noel Chiappa
2017-11-19 17:49 Noel Chiappa
2017-11-19 18:35 ` Arthur Krewat
2017-11-19 13:41 Noel Chiappa
2017-11-19 14:55 ` Clem cole
2017-11-19 21:00 ` William Corcoran
2017-11-19 21:19 ` Ron Natalie
2017-11-19 22:00 ` Dave Horsfall
2017-11-19 22:38 ` Lyndon Nerenberg
2017-11-19 22:40 ` Ronald Natalie
2017-11-19 23:41 ` Dave Horsfall
2017-11-20 1:02 ` Ronald Natalie
2017-11-20 1:18 ` Dave Horsfall
2017-11-20 18:12 ` Random832
2017-11-20 23:22 ` Dave Horsfall
2017-11-20 23:35 ` William Pechter
2017-11-21 0:01 ` Ron Natalie
2017-11-20 19:02 ` Paul Winalski
2017-11-19 14:55 ` Will Senn
2017-11-18 19:23 Noel Chiappa
2017-11-18 21:32 ` Will Senn
2017-11-18 21:49 ` Warren Toomey
2017-11-18 18:34 Noel Chiappa
2017-11-18 18:37 ` Ronald Natalie
2017-11-18 18:40 ` Ronald Natalie
2017-11-18 21:51 ` Dave Horsfall
2017-11-18 21:07 ` Will Senn
2017-11-18 22:53 ` Clem Cole
2017-11-19 1:47 ` Will Senn
2017-11-18 16:39 Will Senn
2017-11-18 18:57 ` Clem Cole
2017-11-18 20:03 ` Don Hopkins
2017-11-18 22:37 ` Dave Horsfall
2017-11-18 23:16 ` Don Hopkins
2017-11-18 23:35 ` Arthur Krewat
2017-11-19 0:35 ` Steve Nickolas
2017-11-19 0:42 ` Don Hopkins
2017-11-19 1:04 ` Clem cole
2017-11-19 16:20 ` Arthur Krewat
2017-11-20 2:33 ` Lawrence Stewart
2017-11-18 21:26 ` Will Senn
2017-11-18 22:39 ` Clem Cole
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