> In one of his books, Wirth laments about programmers proudly
> showing him terrible code written in Pascal
For your amusement, here's Wirth himself committing that sin:
http://www.cs.dartmouth.edu/~doug/wirth.pdf
> From: Nick Downing
> way overcomplicated and using a very awkward structure of millions of
> interdependent C++ templates and what-have-you.
> ...
> the normal standard use cases that his group have tested and made to
> work by extensive layers of band-aid fixes, leaving the code in an
> incomprehensible state.
Which just goes to provide support for my long-term contention, that language
features can't help a bad programmer, or prevent them from writing garbage.
Sure, you can take away 'goto' and other dangerous things, and add a lot of
things that _can_ be used to write good code (e.g. complete typing and type
checking), but that doesn't mean that a user _will_ write good code.
I once did a lot of work with an OS written in a macro assembler, done by
someone really good. (He'd even created macros to do structure declarations!)
It was a joy to work with (very clean and simple), totally bug-free; and very
easy to change/modify, while retaining those characteristics. (I modified the
I/O system to use upcalls to signal asynchronous I/O completion, instead of
IPC messages, and it was like falling off a log.)
Thinking we can provide programming tools/languages which will make good
programmers is like thinking we can provide sculpting equipment which will
make good sculptors.
I don't, alas, have any suggestions for what we _can_ do to make good
programmers. It may be impossible (like making good sculptors - they are born,
not made).
I do recall talking to Jerry Saltzer about system architects, and he said
something to the effect of 'we can run this stuff past students, and some of
them get it, and some don't, and that's about all we can do'.
Noel
I have a ImageMagic CD that I got back in 1994 that I found in my
garage. It has a bunch of versions of linux that aren't on kernel.org.
The 0.99 series, the 0.98 series and what looks like 1.0 alpha pl14
and pl15.
Is anybody here interested in them?
I have fallen out of contact with the Linux folks, so don't know if
anybody on kernel.org would be interested in these. Does anybody care?
Warner
On 2016-12-29 03:00, Nick Downing <downing.nick(a)gmail.com> wrote:
> I will let you know when I get
> it working :) It's not a current focus, but I will return to it someday.
> In the meantime, I'm putting it on bitbucket, so others will be able to
> pick it up if they wish. However, this also isn't my current focus, it's
> there, but it's not documented.
>
> The IAR compiler on the Z180 supports a
> memory model similar to the old "medium" memory model that we used to
> use with Microsoft or Turbo C on DOS machines, that is, multiple code
> segments with a single data segment. Yes, the Z180 compiled C code is
> larger than the PDP-11 compiled C code, but luckily you can have
> multiple code segments, which you cannot (easily) have on the PDP-11.
>
> Unfortunately code and data segments share the same 64 kbyte logical
> address space, so what I did was to partition the address space into 4
> kbytes (always mapped, used for interrupt handlers, bank switching
> routines, IAR compiler helper routines, etc), 56 kbytes (kernel or
> current process data and stack) and 4 kbytes (currently executing
> function). The currently executing function couldn't be more than 4
> kbytes and couldn't cross a physical 4 kbyte boundary due to the
> hardware mapping granularity, but this was acceptable in practice.
>
> I got
> the Unix V7 clone working OK under this model and then added the
> networking, so although it was a bit of a dogs breakfast, it proves the
> concept works. My memory management left a fair bit to be desired (too
> much work to fix) however I think porting 2.11BSD would solve this
> problem since it works in the PDP-11 under split I/D, which has similar
> constraints except the 4 kbyte code constraint. My understanding is
> 2.11BSD is actually a cut down 4.3BSD running on the HAL from 2.xxBSD, I
> would like to audit each change from 4.3BSD to make sure I agree with
> it, so essentially my project would be porting 4.3BSD rather than
> 2.11BSD. But I'd take the networking stack and possibly a lot more code
> from 2.11BSD, since it is simplified, for instance the networking stack
> does not use SYN cookies. cheers, Nick
Having written quite some code on the Z180, as well as god knows how
much code on the PDP-11, I'm going to agree with Peter Jeremy in that I
do not believe 2.11BSD can be made to run on a Z180. (Well, of course,
anything is possible, you could just write a 68000-emulator, for
example, but natively... no.)
Unix V7 is miles from 2.11BSD. Unix V7 can run on very modest PDP-11
models. 2.11BSD cannot be made to run on a PDP-11 without split I/D
space, which effectively gives you 128K of address space to play with,
in addition to the overlaying done with the MMU remappings.
The MMU remappings might be possible to emulate enough with the segment
registers of the Z180 for the Unix needs, but the split I/D space just
won't happen.
2.9BSD was the last version (I believe) which ran on non split-I/D machines.
Johnny
>
> On Wed, Dec 28, 2016 at 6:14 PM, Peter Jeremy <peter(a)rulingia.com> wrote:
>> On 2016-Dec-25 17:21:31 -0500, Steve Nickolas <usotsuki(a)buric.co> wrote:
>>> On Mon, 26 Dec 2016, Nick Downing wrote:
>>>> I became frustrated with the limitations of both UZI and NOS and decided to
>>>> port 2.11BSD to the cash register as the next step, my goal was (a) make it
>>>> cross compile from Linux to PDP-11, (b) check it can build an identical
>>>> release tape through cross compilation, (c) port it to Z80 using my
>>>> existing cross compiler.
>>> A Z180 is powerful enough to run 2.11BSD? o.o;
>> I suspect shoe-horning 2.11BSD onto a Z180 would be difficult - 2.11BSD
>> on a PDP-11 requires split I+D and has kernel and userland in separate
>> address spaces. Even with that, keeping the non-overlay part of the
>> kernel in 64KB is difficult. Equivalent Z180 code is going to be much
>> larger than PDP-11 code.
>>
>> I'd be happy to be proved wrong.
>>
>> --
>> Peter Jeremy
--
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
Since Larry started the wish-listing of people we'd like to see on the
list, I'll add mine:
* Doug Gwynn
* Chris Torek
* Guy Harris
Anyone know how to track down any of these folks?
My two cents. :-)
Happy New Year everyone,
Arnold
As Neil Young said when he played with the band, it's been of one of
the great joys of my life to be here with you (yeah, I paraphrased).
As a kid who wanted to be at Bell Labs, a student who got the troff
manual and used it for the next 30 years, a student who got an account
on the vax 11/750 that had the BSD source on it and learned so much,
I just want to thank all of the Bell Labs people for being here and
Warren for putting this list together and for Unix teaching me so much.
If I could have one thing for Christmas it would be bwk joining the list.
I did some extensions to awk and asked him about it and he tarred up
~bwk/awk and sent it to me. I've got the awk source and the book source
in english and french (I think). Brian is awesome, it would be cool to
have him on this list.
All that said, I super grateful to be here amongst the people who were
there when you got an image from Ken. You guys are lucky.
--lm
[ This whole article is just a flight of fancy; feel free to ignore it or
at least treat it as the whimsy that it is. ]
The PDP-7 Unix system is the first step on the evolution of Unix as we know it.
We have a snapshot of the system around the end of 1970/beginning of 1971 at
http://www.tuhs.org/Archive/PDP-11/Distributions/research/McIlroy_v0/
and a reconstructed and working partial system at
https://github.com/DoctorWkt/pdp7-unix
PDP-7 Unix was a playground for Ken, Dennis and others to try out ideas and
implementations, and it was quickly superseded by 1st Edition PDP-11 Unix.
Details of how it evolved are at https://www.bell-labs.com/usr/dmr/www/hist.html
and https://www.bell-labs.com/usr/dmr/www/chist.html
All fine and good. However, I keep wondering, how far could they have taken
Unix on the PDP-7 platform?
The Kernel
----------
The reconstructed kernel only occupies 3070 words of 4096 words available,
so there is room left for more code. There is already an alternative
reconstruction where the "dd" concept has been replaced with the ".."
concept (see https://github.com/DoctorWkt/pdp7-unix/tree/master/src/alt)
PDP-7 Unix doesn't have the concept of absolute or relative filenames
(e.g. /usr/bin/ls or a/b/c or ../../file), Could the nami kernel function
be modified to do this? It would probably mean changing from two characters
packed into a word to a single character per word (to make searching for
'/' easier), and this would turn it into something more recognisable as Unix.
What about pipes? They should not be too hard to implement. Even sixteen
pipes with a 16-word buffer each would only be 256+ extra data words in
the kernel. And a hundred words of code?
There are only a few special devices in the kernel: ttyin, ttyout, keyboard,
display, pptin, pptout. What about a disk block device? Was there a PDP-7
tape device, and if so, why not a tape driver and block device?
Filesystem
----------
The implementation of the filesystem is, in some places, quite inefficient.
The free block list is implemented as follows. In each block, there are
10 free block numbers then a pointer to the next part of the free list.
However, each block can hold 64 block numbers, so why are only 10 free
block numbers stored in each block? By using the whole of a block to store
free block numbers, there would actually be more free blocks to use!
Each i-node (size 12 words, 7 of which are direct or indirect pointers)
has one word which holds a unique value. This doesn't seem to be used at
all. If it was reused as a block pointer, this would allow files to be
up to 8*64=512 (small) or 8*64*64=32768 (large) words in length, instead of
7*64=448 words (small) or 7*64*64=28672 (large) words.
The system is set up to only use one side of the two-sided disk device.
It looks like the other side was used to backup (snapshot) a working
system in case of catastrophic filesystem corruption: they could simply
copy the blocks from the "snapshot" side back to the working side. We
could double the size of the filesystem quite easily.
Macro Assembler
---------------
The kernel is written using fairly tight assembly code, and there probably
isn't a way to translate it into a high-level language. The PDP-7 has an
arcane instruction set, and the existing assembler syntax is nothing special.
What about a macro assembler that makes it easier to write code, especially
readable code? Here are some ideas based on the existing kernel:
u.rq := 8 ==> lac 8; dac u.rq
function swap ==> swap: 0
{
return; jmp swap i
}
subroutine .fork ==> fork: line 1 // i.e. not a function
{
line 1
}
loop ==> 1:
{
} jmp 1b
if (sad dm1) ==> sad dm1
{ jmp 1f
code1 code1
} else { 1: code2
code2
}
betwen(o101,o132) ==> jms betwen; o101; o132
There are probably a bunch more that could be added. The aim is to
make the control structures easier to read and write. The programmer
still has to grok the PDP-7 instruction set.
B (or other) Language
---------------------
PDP-7 Unix has a B compiler while compiles source down to a virtual
instruction set which is interpreted by the B interpreter. We have the
B interpreter code, and Robert Swierczek managed to rewrite the B compiler,
see https://github.com/DoctorWkt/pdp7-unix/blob/master/src/other/b.b
At first glance, the PDP-7 architecture is not that amenable to high level
languages, but it turns out that it is indeed possible to write a compiler for
a C subset that targets the PDP-7, see https://github.com/DoctorWkt/a-compiler.
So, could the B compiler be modified to actually output PDP-7 assembly code?
If so, we could rewrite the utilities (cp, mv, ls etc.) in a high-level
language and make the system easier to maintain. I would recommend treating
int and char as the same and only storing one char per word.
And then, even though the PDP-7 architecture doesn't support it, how hard
would it be to add int/char types and bring the language one step closer to C?
Conclusion
----------
All of this is pie in the sky. It can certainly be done, but a) who has
the time and b) it would be a "tour de force", nothing really useful. But
imagine if, at the beginning of 1970, Unix had a proper B or C compiler,
utilities written in this high-level language, a kernel written in a semi-high
level language, and a system with pipes and proper pathnames.
Cheers, Warren
Let me be the first to say that the International Earth Rotation Service
has announced that there will be a Leap Second inserted at 23:59:59 UTC on
the 31st December, due to the earth slowly slowing down. It's fun to
listen to see how the time beeps handle it; will your GPS clock display
23:59:60, or will it go nuts like my last one did (I had to power cycle
the thing)?
My recording of the last one: horsfall.org/leapsecond.webm .
--
Dave Horsfall DTM (VK2KFU) "Those who don't understand security will suffer."
