2026-01-12: International friends, since this is new release, shipping will be limited within US. Please stay tuned.

My Brain-In-A-Jar Project

Here is the transputer shield you have been waiting for :) Transputers are pioneering processors designed by INMOS, around 1980's, specifically for multi-processor architectures. Each processor has 4x serial-links that can talk to other transputers. This way, it was possible to connect as many as 256 transputers together for high performance computing. INMOS also released superb documentation and extensive software tools to make life easier for programmers. Unfortunately, transputer computers were mostly add-on cards to PC's running DOS so it was a bit hard to play with them. Until now...

The Retroshield Transputer:

• Designed for 32-bit transputers (T4xx or T8xx series).
• Kit comes w/ T805 (w/ FPU) or bring your own.
• 16MBytes Exterrnal Memory for transputer (PSRAM chips for Teensy4.1 provided)
• Teensy can do 100,000 memory transactions/second (SLOW compared to pure hardware implementation)
• iserver runs on Teensy, using SD Card as "C Drive" and UART as "Console"
• You can run BTL files (the OCCAM/C compiler toolset can also run the transputer albeit slow due to large file accesses)
• minishell, a DOS-like environment for basic file operations on SD Card
• INMOS's F folding editor can run (I found key bindings difficult to remember)
• Transputer MINIX runs too (thought not much to do)
• WARNING: Due to wide range of software and hardware available for transputers, please consider this shield as indefinitely experimental.

NOTE: This shield requires Teensy adapter

External Memory interface is SLOW!

Transputer has fast internal 4K RAM (1-cycle access) but INMOS tools dont fit there. For external memory interface, I had to use parallel/serial shift registers for 32-bit address and 32-bit data bus (not enough pins on the MEGA headers). This shifting gives us about 100,000 transactions/second, which is enough (in my opinion) to play with BTL files. For comparison, a true hardware dynamic RAM implementation would give 4 to 8 million transactions/sec (dynamic rams with access time ranging from 125ns to 220ns).

• OCCAM/C compilers can be executed on the transputer but they are slow because they process big library files (1MB's) via iserver. As a result, OCCAM and C compilers/linkers take 5 - 10 minutes to read library files and link the code.
• Therefore if you want to develop code, it is better to use a PC based transputer emulator (two links provided in documentation) so you can go through the code/compile/test cycle in seconds.

What do you get?

Following options are available:

• Asembled and tested
• Kit including T805 transputer (you solder through-hole parts)
• Kit without transputer (Bring your own)
• PCB only (SMT parts already soldered for you)

Sorry, prices are a bit higher than normal because of 50% import tariffs.

What makes it special?

I started Retroshields in 2019. Implementating Transputer shield hardware and software has been the "pinnacle" of my engineering :) I used clever tricks to keep the hardware simple and implementing SW side of things was a challenge. Teensy has to run three tasks in parallel (cpu-tick, link-loop, and iserver-loop). Getting the INMOS compilers running on the retroshield wouldn't be possible without the amazing transputer/iserver emulation originally done by Julian Highfield and well done INMOS documentation.