5447173fec
The naive order of the assembly files given to the assembler was to put the st?.s files first followed by fop.s at the end. This caused Space Travel to crash, why that happend is explained below. st1.s through st5.s contain code, while st6. and st7.s contain constants and data storage respectively. The order of the given assembler files meant that the code st?.s ended up at 010000 onwards, while the code in fop.s ended up after the data storage defined in st7.s. In particular the function fmp ended up immediately after dspl. At the end of st7.s there is a display list, dspl. At runtime this list is pointed to by the clistp variable stored at the auto-indexing memory register at address 017. Auto-indexing means that the pointer will be incremented after use. However the display list dspl does not reserve memory for the entire list, instead it assumes that the memory immediately after dpsl is unused. This conflicts with storing fmp from fop.s immediately after st7.s! Despite this conflict the first few frames of space travel could be rendered because clistp was never referenced. By the time it was referenced it changed the code in fmp to invalid code. At a later stage when fmp was called the program crashed. The solution I chose is to reorder the files at the command-line given to the assembler; specifically I opted to put fop.s after all the code in st1.s though st4.s. This means that Space Travel now runs without crashing!
pdp7-unix
About
pdp7-unix is a project to resurrect Unix on the PDP-7 from scans of the original assembly code done by Norman Wilson. The scans of PDP-7 Unix are in the Unix Archive as the files 0*.pdf.
Current Status
January 2020
Unixv0 is running on a real PDP-7 at the Living Computer Museum. Youtube.
October 2019
A second notebook with missing sources has been discovered and scanned. New files are being added to the scans directory as they are typed in!
March 2016
We've written an assembler, a user-mode simulator and commented several source files. We now have these utilities running: as, cat, chmod, chown, chrm, cp, date, ln, ls, mv, stat. We have a working shell with some functionality missing. We have a working filesystem and we can now boot the kernel, launch init, login, get to a shell prompt and run the utilities.
Things to do: bring the system fully up on a PDP-7 system, fix any bugs and document everything. We have a real PDP-7 and SimH as target platforms.
Building pdp7-unix
pdp7-unix requires Perl5 to build.
To compile it:
make
Running pdp7-unix
You will need simh 4.0 to run pdp7-unix. You can get the source code here. On 64-bit systems, you may need to set the C compiler's optimisation level to -O1.
Running from source
To run pdp-unix from the pdp7-unix source tree, do:
make run
Press ctl-e to break out the simulator into simh
Typical Output
A typical pdp7-unix session on simh looks like:
pdp7 unixv0.simh k PDP-7 simulator V4.0-0 Current git commit id: b848cb12 CPU idle disabled 8KW, EAE /Users/tom/projects/pdp7-unix/build/unixv0.simh-13> att rb image.fs RB: buffering file in memory /Users/tom/projects/pdp7-unix/build/unixv0.simh-17> att -U g2in 12345 Listening on port 12345 PDP-7 simulator configuration CPU idle disabled CLK 60Hz, devno=00 PTR devno=01 PTP devno=02 TTI devno=03 TTO devno=04 LPT disabled DRM disabled RB devno=71 DT disabled G2OUT devno=05 G2IN devno=43-44 login: ken password: ken @ ls .. dd maksys.s s1.s s2.s s3.s s4.s s5.s s6.s s7.s s8.s sop.s system sys.rc trysys.s @ ls system .. adm apr as b cas cat check chmod chown chrm cp date db dd display ds dskres dsksav dsw dttt ed init keyboard link list ln ls moo mv nm od p password pptin pptout rm rn roff salv sh stat tm ttyin ttyout ttt un @
Source Tree
The code in the original scans are (c) Micro Focus who own the rights to the Unix source code. Everything that didn't come from the scanned files is GPLv3.
- /build is an area to build the kernel & filesystem and run them
- /man holds man pages
- /misc holds miscellaneous notes and information
- /scans holds the unmodified OCR versions of the scanned files
- /src/cmd holds the modified source code of the user-mode programs
- /src/sys holds the modified source code of the kernel
- /src/other holds PDP-7 source code which did not come from the scanned files
- /tools holds the source for the tools written to assist the project
License
pdp7-unix is under the GPLv3
Mailing List
We have a mailing list for those people actively involved in the restoration effort. Send e-mail to Warren Toomey (DoctorWkt) if you are keen to help out.