As attached, thanks to someone over on the RTTY list; not sure if it's
exactly what he wanted.
--
Dave Horsfall DTM (VK2KFU) "Those who don't understand security will suffer."
---------- Forwarded message ----------
Date: Sat, 26 Mar 2016 18:52:59 -0700
From: tony.podrasky
To: Dave Horsfall <dave(a)horsfall.org>
Subject: Re: [GreenKeys] Teletype simulator? (fwd)
Hi Dave;
Attached is my TTY test program.
It is fairly simple. The only thing that might be
tricky is the type of UAR/T you are using.
Let me know if it compiles.
regards,
tony
On 03/26/2016 06:33 PM, Dave Horsfall wrote:
> On Fri, 25 Mar 2016, tony.podrasky wrote:
>
> > What do you mean, "a non-Windoze" TTY simulator?
>
> One that's in source form, not binary...
>
> > One of the programs I have takes e-mail and prints it on a 5-level ITA#2
> > machine.
> >
> > It is written in "C", and at such a low-level that it should compile on
> > ANY thing that runs "C".
>
> Got a copy you can send me to pass on?
>
--
"I read somewhere that 77 percent of all the
mentally ill live in poverty. Actually, I'm more
intrigued by the 23 per cent who are apparently
doing quite well for themselves." -Jerry Garcia
On 2016-03-24 03:00, "Ron Natalie"<ron(a)ronnatalie.com> wrote:
>
>> >Closest I've ever been murdered was when I "accidentally" filled the local
>> >11/70 with an uninterruptible instruction sequence."
> SPL instruction. The PDP-11 was odd that while SPL was a "privileged"
> instruction, rather that trapping if you did it in user mode, it just
> "ignored" it.
> Well, what it ignored was the actual change of the processor level. What
> it still implemented was the side effect was that interrupts were locked out
> until the next instruction fetch.
> If you filled your instruction space up with SPLs you could lock up the
> computer so that even the HALT key didn't work (you had to do a bus RESET).
Ok. Color me stupid, but I don't get it. I totally do not understand how
this locks anything out.
It is the normal behavior of any instruction that interrupts are not
recognized until the next instruction fetch. This is how the microcode
works, and it is also pretty much the same in any processor today.
Except for instructions that take a long time, and which can be
interrupted in the middle, the context preserved, and the instruction
restarted and continued, instructions are normally atomic. You cannot
get interrupts in the middle of an instruction.
Second, I cannot understand how filling the memory with SPL instructions
(or any other instruction) can lock out the CPU. As noted, they are
individual instructions. You still get a fetch between each instruction,
at which point, interrupts will be recognized.
Now, if you instead talked about actually raising the CPU to SPL 7, then
I agree that no interrupts will happen. But that is because you
essentially disabled interrupts.
The front panel still works though. It is not handled like an interrupt,
but it is true that it do interact with the processor states, and
normally if you pull HALT, it will only halt when it's going to fetch
the next instruction. You can, of course, also set the front panel
switch for single microcode instruction, at which point the CPU will
halt at the next microcode instruction instead, and you can single step
the microcode as well.
The one CPU I know you can sunset is the KA10 (PDP-10). I'm sure there
are others, but I have never seen how this could be done on a PDP-11, so
I'm most curious about this, and if you can provide more details I would
be most interested. As I also happen to know where a PDP-11/70 is
standing, I intend to test this out next I get close to it.
As for the KA10 (I think it was the KA10, but it might have been the
PDP-6), the problem is related to the indirect addressing feature. Since
memory is 36 bits, but addresses only 18, you have plenty of bits to
play with. And one of them is the indirect bit. And if you refer to a
memory location that also have the indirect bit set, you get another
memory access to get the actual content. The fun thing happens if you
set the indirect bit, and give your own address. This is then an
infinite memory reference. And the KA10 can not be broken out of that
lookup. The only solution is to pull the power plug.
The CPU is essentially stuck in one state, just tightly reading memory,
and then repeating reading memory. Later PDP-10 models have an explicit
check in the microcode in this loop to be able to break out of this.
Sorry for the offtopic content. :-)
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt(a)softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
On 2016-03-26 20:43, Clem Cole<clemc(a)ccc.com> wrote:
>
> On Fri, Mar 25, 2016 at 11:09 PM, Charles Anthony <
> charles.unix.pro(a)gmail.com> wrote:
>
>> >And Dec's RADIX-50, packing 3 characters into 16 bits. (IIRC the origin of
>> >the 6.3 filenames. bit I can't document that.)
>
> ​Sort of.... before ASCII, DEC used a few other 5 bit codes that were
> around such as baudot​ (look at the PDP-1/4 etc and KSR 28). RAD50 was a
> natural scheme for storing file name and using bits efficiently.
>
> Which, of course, lead to the abomination of case folding - it's not a bug,
> it's a feature 😂
>
> RAD50 gave us the x.y file name form with the implied dot et al. 6.3 and
> later 8.3 were natural directions from that coding. Using the .3 ext as a
> type tag of course followed that naturally given that's all that was stored
> in the disk "catalog." [And CP/M and PC/MS-DOS inherit that scheme -
> including the case folding silliness even though by that time all keyboard
> were upper and lower case and they stored the files in 8 bits].
Some other people already mentioned this, but... - SIXBIT. DEC might
have used baudot in the very early machines, but I would say that SIXBIT
dominated here for a long time. We see it both in the PDP-8, but also
the PDP-6 and its follow ons. RAD50 was the natural extension of SIXBIT
on a machine that did not have a word size that was a multiple of 6.
The x.y filename, as well as the 6+3 pattern predate the PDP-11. I would
say that in this area, the PDP-11 didn't come with anything new, but
just made life more complicated.
OS/8 for sure only have 6+2 filenames, but still in the x.y form.
TOPS-10 have, I think, 6+3. And the Monitor (I think that was the name
for the PDP-6 OS) was, I think, also 6+3.
And it was all SIXBIT.
And SIXBIT also give you the case folding.
I say the PDP-11 complicated life just because DEC was already so much
into having filenames stored more compact than normal text, and having a
6+3 pattern, so they came up with R50, which fits the bill, but it's
more headache than it was worth, if you ask me.
Since the PDP-11 have 8 bit bytes, it would have made much more sense to
just store filenames as 8 bit bytes. It would have cost some more
storage, but not that much. But it took time for DEC to realize that the
space savings here were not really a good tradeoff. Old habits die hard,
I guess.
By the way, RSX (and early VMS) actually use 9+3 filenames.
> UNIX of course, would put the "type" in the file itself (magic #) and force
> the storing of the dot, but removed the strict mapping of name and type.
> Having grown up in both systems, I see the value of each; but agree I think
> I find UNIX's scheme better and lot more flexible.
I think I agree on the point of having filenames in a free format. Not
sure I really like storing the type in the file itself. So I'm sortof
torn. Or rather, I would like to keep type separate from both.
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt(a)softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
Hey All,
I just saw in another thread the statement their are no odd requests here.
So I thought I would test that.
The day NeXT took over Apple I read a page somewhere on the internet that started with line.
Bow down to UNIX children of Macintosh... It then when on its Old Testament conquering tone about the new way of computing that was coming.
Does anybody have any idea who wrote this or where to find it?
Thanks,
Ben
Hello everyone,
I am Rocky and this is my first message. Before starting, I would like to thank you for all the valuable informations and stories you post here.
About the History of Unix, I was wondering with another guy why the rc script has that name. As many of you already know, and according to NetBSD, FreeBSD, OpenBSD (current) manual,
"The rc utility is the command script which controls" the startup of various services, "and is invoked by init(8)" (from DESCRIPTION).
"The rc command appeared in 4.0BSD" (from HISTORY).
Words may slightly change between the three distributions, but the meaning and the informations provided are the same. So, the etymology of rc does not appear in the man pages. Do you know how to recover it? Do (or did) the letters rc have some meaning in this context?
Cheers,
Rocky
On 2016-03-25 00:27, Milo Velimirovic wrote:
>
>> On Mar 24, 2016, at 6:06 PM, Johnny Billquist <bqt(a)update.uu.se> wrote:
>>
>> On 2016-03-24 23:50, Peter Jeremy wrote:
>>> On 2016-Mar-24 11:17:18 +0100, Johnny Billquist <bqt(a)update.uu.se> wrote:
>>>> It is the normal behavior of any instruction that interrupts are not
>>>> recognized until the next instruction fetch. This is how the microcode
>>>> works, and it is also pretty much the same in any processor today.
>>> ...
>>>> individual instructions. You still get a fetch between each instruction,
>>>> at which point, interrupts will be recognized.
>>>
>>> Some instructions inhibit the "check for interrupts at the end of this
>>> instruction" check. I'm most familiar with the 8080 EI instruction,
>>> which enabled interrupts after the following instruction (so things like
>>> EI;HLT didn't have a window). It seems the PDP-11 SPL behaves the same.
>>
>> I don't think it should on the PDP-11, and the documentation do not mention any such thing.
>> There is a good reason the 8080 (and Z80, and others) have this property. The RETI instruction on these machines do not enable itnerrupts themselves, so just as you note, you need to both enable interrupts and return from interrupt atomically, or else you get into a mess.
>>
>> The PDP-11 RETI instruction changes the processor priority as a part of the instruction. You do not use SPL (whatever) before a RETI.
>> Thus, it do not make sense that SPL on a PDP-11 would have this property. If if indeed do disable recognizing interrupts after an SPL, it sounds more like a bug. I guess I'll go and read the microcode so see if that mentions any of this, since I'm sortof into reading it anyway as I was trying to debug a problem on an 11/70 only a couple of months ago…
>
> The PDP-11 has no RETI instruction; it has a RTT (ReTurn from Trap) and a RTI (ReTurn from Interrupt) instructions, but you already knew that, right? In some cases it’s problem that it’s not possible to determine which is appropriate or correct to use. According to the PDP11 Architecture Handbook the difference between them is in what happens when the RTx instruction loads a PSW that has the T bit set and when it forces a Trace trap. RTI - immediate trap, RTT traps after the instruction following the RTT.
Oops. Yes, it's RTI and RTT. But the names are beside the point, and so
is the difference between these two. The point is that the
instruction(s) do set the processor priority level, and you do not use
SPL in combination with them, so it makes no sense to have SPL inhibit
interrupts for any length at all. (And yes, I did know that.)
Oh, and as far as RTT vs. RTI goes, not it's not hard to know which one
you want. You want RTT for your debugger and RTI for everything else.
The difference is about what happens after the return. With RTT, the
T-bit trap will not trap until another instruction has executed. With
RTI, you would never manage to step to the next instruction with the
T-bit, since every time you returned, you'd get another trap.
But I bet you knew that as well... ;-)
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt(a)softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
Seems like we are all contributing old card stories.. here is one of my
favorites from my past.
At CMU, all systems programmers working for the computer center had to put
shifts in as the operator behind the "glass door" doing the grunt stuff
(but we got all the computer time we wanted, an office and terminal - so it
was a good deal in those days). The student courses, in particular the
engineering intro to FORTRAN (WATFIV), used the TSS based 360/67 which we
programmed and ran; but they used the batch system on cards not timesharing
with the ASR 33's which was quite expensive. There was a traditional glass
room with the computer, its tapes and other gear, and a counter with a
"call human for help" button where "paying users'" could come ask questions
of the operator on duty. On the older side of the counter was the flock
of keypunch machines and a high speed card read. The printers were in
secure areas, so we would bring out student prints from their batch jobs as
needed and put them on the binds near the counter ( as was the pretty much
the standard of those days).
By rule, the system's programmers were also not supposed to help the
students with their assignments. They were supposed to get help from their
TA's and Profs, *etc*. who had regular hours. But often folks were up
very late working on assignments and no one from the course was around to
ask questions. And as the operator, if you had a minute, it was not
uncommon to have a little empathy for your brothers and sisters in arms on
the other side of the counter. As long as this was not abused, the TA's,
Profs as well as our bosses in the computer center tolerated the process.
But if we were obviously busy, we really did not have the time to do much
to help them.
One night I was working the over night operator shift with another coworker
who will be left nameless (but I will say that he's now a SVP at a large
computer firm these days). It was a very busy night for us for some
reason, probably something like printing bills, or checks for the school or
some such; along with a full backup, so we had our hands full between
mounting tapes, changing types of paper and print heads *etc.*, security
procedures with the results and the like. That night, there was also a big
assignment due shortly for one of the classes.
Sure enough the buzzer started ringing and it was a frustrated (and as I
remember somewhat clueless) student that needed help with his assignment.
He was claiming that the his deck was being rejected/was not working.
Note "turn around" from deposit card deck to receipt of print out was
probably in the order of 10-15 minutes, and sometimes longer. One of us
came out, showed him something like a missing "BATCH WATFIV" command card
or some such and reminded them of the official policy and probably pointed
to the sign, as we were very busy with our job. We would politely tell
them to try to find a TA or someone in the class that could help him.
The student went away, and we went back to work. A few minutes later the
buzzer went off again, same student, and the cycle repeated with some other
trivial issue. After the 4th or 5th time it was becoming a real issue
because we were really quite busy. At that point, my coworker came out and
said, here bring me your deck. He looked at them and quickly said -- "The
problem is you used the wrong color cards."😈
The student was completely dejected and walked away. I looked up and
said, man that was cruel. But it did buy us time to finish our work.
Never found out if he re-keypunched his cards.
Clem
Steve Johnson:
This reminds me that someone at BTL threw together a "TSO Shell". It was
a wrapper around /bin/sh that slept for 10 seconds before executing each
line...
=====
And after each command exited. Discarding anything typed ahead
during the sleep, of course.
And printed all-upper-case IEFCRAPNONSENSE messages even when a
command exited successfully.
I think I still have a copy somewhere. It dates from the 6/e era,
so it would need a lot of work to compile and run on a modern system.
Occasionally I think of converting it to ISO and POSIX even though
that seems contradictory somehow.
Norman Wilson
Toronto ON
