[TUHS] Porting 2.11 BSD

Oliver Lehmann lehmann at ans-netz.de
Wed Nov 25 20:14:51 AEST 2015

Al Kossow <aek at bitsavers.org> wrote:

> On 11/23/15 12:40 AM, Erik E. Fair wrote:
>> The undergrads who used that system to learn Unix ported many
>> a BSD
>> utility to that system (at least the ones that weren't too RAM-hungry),
>> starting with BerkNet so we could move files around easily & have E-mail.
> That reminds me that you are going to run into utilities that use the
> overlaying ld that jumps through hoops to get large programs (vi) to  
> run in a 16 bit address space.

Good point. I was also thinking if 2.11 is realy the right choice to use
for porting. From what I understood:

- The PDP11 can only access up to 64KB address space.
- 2.11 uses overlay to "show" and "hide" memory into this 64K address

A Z8001 can address up to 128 segments of 64KB. Means, a single array can
only be up to 64KB, but you can have 8MB of memory per "section". My system
has 3 MMUs while one is dedicated to the code section and one to the data
section. So my Code section can be max up to 8MB and my data section can be
up to additional 8MB. Currently my system has up to 5.5MB of RAM (but can
be upgraded to 16MB easily)

I was thinking if 4.3 BSD would be better to port as the whole overlay logic
which is implemented in 2.11 could make 2.11 maybe to complex to port? I
mean, all this overlay logic would not be needed for the Z8001 and it maybe
would not even work. (remember - I plan to use my existing SYSIII compiler
which knows nothing about overlaying!)

What I understand for 4.3 BSD is, that it is meant to run on machines with
a memory configuration where the memory is adressable in "one block" which
is of course not true for the Z8001. But - the compiler/assembler handles
all this adressing for C code so why should it be imported on how the is
addressed internaly?

Additionaly, my system has NO floating point support. The current SYSIII
uses a lengthy floating point emulation Assembler Source to "work around"

I saw, that 2.11 also has some FPU-emulation. What about 4.3?

Could 4.3 be a better choice? If so - which 4.3 should I use?

In general - I'm looking for a good target OS. It should be not too
complex (-> "modern") but should provide a TCP/IP stack which is my
main motivation in porting at all.

> I'll dig through my archives and see if there was a Z8000 version of pcc
> in the MIT compiler kit.

That would be great - maybe you could also answer my private mail about
the Onyx C8002 I sent you some days ago ;)
The compilers for Z8000 I found so far where either able to address 64K
only, or where able to only generate COFF-format objects which I can't
link on my SYSIII...


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