This is an updated version of Dave Cheney's CPP11 which will run on a Pi Pico. For this project I have selected th

GitHub - Isysxp/Pico_1140: A PDP11/40 emulator that will run Unix v5/6

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2023-03-17 01:30:08

This is an updated version of Dave Cheney's 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 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 ( which is included in the repo. The project environment is for Visual Studio Code. The Pico SDK is also required This is not included.

The de facto emulator for most old computers is 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 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 ( 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.

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.

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