A PDP11/40 emulator that will run Unix v5/v6 and a number of DEC operating systems.
Introduction and acknowledgements:
This is an updated version of Dave Cheney's CPP11 https://github.com/davecheney/cpp11 which will run on a Pi Pico. For this project I have selected the Sparkfun Thing Plus board which contains an RP2040 chip, an SD card and 16Mb flash. See https://www.sparkfun.com/products/17745. Other hardware may be used including a Pi Pico itself. Wire the SDCard as per the Sparkfun schematic. The SD card interface uses Karl Kugler's app (https://github.com/carlk3/no-OS-FatFS-SD-SPI-RPi-Pico) which is included in the repo. The project environment is for Visual Studio Code. The Pico SDK is also required https://github.com/raspberrypi/pico-sdk. This is not included.
The emulator:
The de facto emulator for most old computers is Simh https://github.com/simh/simh. The size and complexity of the individual machine apps is such that a direct port to a memory limited system is not feasible. This is the reason for basing the system on a lightweight emulator as provided by Dave Cheney for the ATMEGA2560 https://github.com/davecheney/avr11 and the C++ version above. The code has been updated with patches to the KL11/KT11/KB11/RK11 systems so that the Pico SDK services may be used. The 11/40 FIS has also been added an this is not a true simulation as found in Simh but an optimised emulation. The emulator will run the instruction test and EIS MAINDECS. It fails the traps tests as a stack limit trap and trace trap are not implemented. Similarly, the KT11 test fails as the maintainence mode is not implemented. Finally, the FIS test fails as the implementation of this uses translation of DEC floating point to IEEE 754. The app is sufficiently accurate to run RT11 V3/V4, Unix V5 and V6 and mini-unix (http://www.tavi.co.uk/unixhistory/mini-unix.html). I would note that the floating point performance for Unix is rather slow. It will also run MINC Basic for which I have included an RK05 image which has the limitation that some command will return to the RT11 . prompt. The original version uses a modified RX02 monitor. There is a KW11 line time clock. The implementation is not good and system time will not be accurate.
Building:
The app is provided as a Visual Studio Code project. Firstly, a copy of the Pico SDK is required in the same top level directory as the app. The path to the SDK will need to be setup on your system. Also, GCC of at least version 10 is required. This may need to be installed and selected as the active kit. The build process will create a .uf2 binary in the build directory. This can be copied to the RP2040 via the virtual drive presented by the RP2040 boot system. Any number of RK05 disk images may be copied to the root of an SDCard formatted to FAT32. I use a 32Gb card and the SPI system works with this. The images are in the same format as used by Simh and may be built or modified in Simh prior to use.
Booting:
After inserting an SDCard and resetting the card, a COM port will appear. Connect a terminal app to this eg TeraTerm. The images on the SDCard will be listed with an index that is used to select the boot volume. The system boots using a boot rom in bootrom.h at address 2000. The start address is set in setup(..) in avr11.cxx. At present, only 1 volume can be attached at a time. Typically, unix images prompt with a '@', then type unix or rkunix to boot. The switchregister is set by default to 0173030 in KB11::reset which will boot unix in single user mode. In addition, the app contains a binary loader which can be called from setup(...) as above with a suitable change to the cpu start address. You can load a binary tape from the SDCard if the name of the tape image starts with 'maindec'. The default start address in 0200;
Unix: It is sooooo easy to trash these old unix volumes! It is a good habit to 'sync' a lot of times just in case something does go wrong!
Update: 20/12/2022
I have now added an RL01/2 driver to the system. By default, the app will attach rt11V.dsk to unit 0. Please make sure this file is on the SD Card (copy is in images). The logic in this driver is slightly different to the RK11 driver in that I/O is defered for 10 CPU cycles. This is due to some curious behavior of RT11 in that without this option, the 'R' command does not work correctly whereas 'RUN' does. After the system has booted into RT11 V4.. .BOOT DL0: This will bring up RT11 V5 from the RL02 image.
On this image there is a copy of the DECUS c compiler. This only compiles really odltime c. Documentation in images directory.
As a test of this system, you can have a really good laugh and run PDP8.sav...
.r pdp8
Argv: (just press return)
PDP8 Emulator
->B (need ucase)
->R 200 (need ucase)
. (now you are running the 4K PDP-8 DMS system.)
.FCL
CONGRATULATIONS!!
YOU HAVE SUCCESSFULLY LOADED 'FOCAL,1969' ON A PDP-8 COMPUTER.
SHALL I RETAIN LOG, EXP, ATN ?:YES
PROCEED.
So, now you have an emulated PDP-8 runnning on an emulated PDP-11 .... Rabbit hole or what!!!! See PDP8.COM for the command lines to build this app and PDP8.C for the source code.
Have fun, Ian Schofield Dec 2022.
Update Jan 2023
I have committed a substantial update to the code base which has been in test for some time.
The major features are:
- Added an RL01/2 handler. The image and boot device can be selcted from the initial dialogues.
- Updated a significant problem with register mapping into I/O space. This is only a partial fix. See KB11.H for the apparently trivial changes.
- Minor changes to other handlers to allow for the below.
- Added a suitable minimal RSTS/E image which is built to use the FIS instruction set.
- Added a suitable minimal Multi-User BASIC image.
It has turned out to be quite complex to allow for the function of UNIX/RT11/RSTS/MUBAS as they all have some interesting differences.
Due to the changes, it remains possible that something will have broken.
Any comments welcome.
Ian Schofield Jan 2023
Update Jan 2023
This is a major update with many minor change. The most important point is that the app has now gone multi-user!
I have added and extra DL11 interface. If you use a SparkFun board, upload the .uf2 in the images directory.
2 comm ports will appear ... connect a terminal instance to both of them.
For thse who wish to build the code .... edit tusb_config.h in Pico-SDK\src\rp2_common\pico_stdio_usb\include<br>
#define CFG_TUD_CDC (2)
(I hope this works for you)
This required quite a lot of changes to the app and to the supported operating systems:
- RT11. RT11_V5_CFB: Fortran/Basic/C.
- RT11_V5_MUBasic: Multi user basic. Boot to RT11XM and run MUBASX. Type '2user' for the config file.
- Unix_V6: I have rebuilt the kernel to add an extra DL11 device. You should see a login in both terminal windows.
- RSX_31_Fortran: This image boot RSX11/M in 2 user mode. This is a very complex OS. Best of luck!
- MINC_BASIC is as before and boots to a 'READY' prompt.
- Rsts_DL: This boot Rsts/E in multi user mode. A bit easier to use than RSX/11.
You may note that these operating system have one thing in common (except Unix) ... this is BASIC.
The history and logic behind this is very interesting in that DEC's view of the language to use was Basic!. This was at a time just prior to c appearing and it was believed that Fortran was not the language of the future. As it happens, I am a Basic fan and I still use VB.Net for a number of projects. But c was in the pipeline and one of the RT11 disc contains DECUS c. The rest as they say is history but I have to say that I am not keen on Rust etc.!
Ian Schofield Jan 2023
Update Mar 2023.
Many thanks to Bruno Novak for his work on sysgening various versions of RSX11M to include Cobol, Fortran and Basic Plus 2. It became apparent that there was a significant problem with the emuation. I have traced this to the original use of 16bit IOPAGE addresses used to reference the major registers. These references did not use a valid address and bypassed the KT11 memory mapping system. This has been corrected and the details are in KB11.CXX. All of the above compilers and runtimes pass some very basic tests. At some stage, an RSX11M image wil be made available.
Ian Schofield Mar 2023
Update Mar 2023
Bill Saltzstein has created a battery powered Pico_11/40 with a BLE interface. Do read the enclosed paper.
Bruno Novak has built a version of RSX11 4.6 BL56 with a C compiler and a Y2K compliant version of TIME.
Update September 2023
Pico_1140 now has an FP11 device! To avoid re-inventing the wheel, I have used a copy of the FP11 emulator from SIMH.
Please note the GPL license in the header of fp11.cxx as this was written by Bob Supnik and I would not presume to add my name next to his.
This is in addition to the existing FIS code in kb11.cxx. This required some minor changes to interface with the Pico_1140 environment.
Those of you who are DEC experts will immediately point out that the 11/40 never had an FPP and the 11/45 does not have a FIS option.
So, the Pico_1140 is a somewhat hybrid system. So far as I can tell, this does not seem to cause a problem.
The reason for adding this option is to be able to run more recent version of RSX11 and RSTS/E. RSTS/E was a particular
problem in that most builds on the web need an FPP to run Basic. There is just enough memory to run RSTS/E V 9.3.
(Having said this, there is a sysgen option to use FIS if you wish).
Further to the memory limit of the Pico, there is no point in going for 22 bit addressing. This option is being considered
as part of a parallel build for the ESP32 with PSRAM (4Mb). This is WIP
In the meanwhile, have fun and try some apps that need an FPP.
Ian Schofield September 2023.