AT to XT Keyboard Protocol Converter firmware + schematic
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AT-to-XT Keyboard Protocol Converter

Build Status

This repository provides the source, schematics, and Gerber files that converts the AT-keyboard protocol to the XT keyboard protocol. As XT keyboards are expensive (seriously, type in "PC XT keyboard" or "PC 5150 keyboard" in Ebay), this provides a cheaper alternative for someone willing to wait for PCB and parts. This circuit supports 101-key extended keyboards using the XT protocol, but older pre-386 systems may not know how to handle extended keys. The extended keycodes are based on a document from Microsoft that includes XT keycodes for compatibility.

Rust Source

As an experiment to test the MSP430 Rust/LLVM backend, the current source has been rewritten in Rust. All future development will be in Rust. The rewrite is not exactly semantically equivalent to the C source code; in particular, in the Rust version, the keyhandling Finite State Machine (FSM) returns immediately and I/O processing occurs in the main loop. In the C version the FSM is the main loop, and I/O processing is embedded.


This source requires the Rust nightly compiler for the foreseeable future. To obtain the nightly compiler and relevant dependencies:

  1. Visit the rustup website and follow the instructions to first get a stable compiler. I have only tested the GNU ABI version of Rust on Windows, but choose which version makes sense for you.

  2. rustup should now be on your path. Obtain the nightly compiler with: rustup install nightly. As of before July 16, 2017, MSP430 support is enabled in Rust nightly. Switch to the nightly compiler by running: rustup default nightly.

  3. MSP430 needs a libcore installed that doesn't conflict w/ your host. The xargo program allows a developer to maintain multiple libcores for multiple archs simultaneously: cargo install xargo.

  4. Obtain msp430-elf-gcc from TI at the bottom of this page, and make sure the toolchain's bin directory is visible to Rust. As I understand it, the GCC toolchain is required because Rust is hardcoded to call the compiler driver to assemble if LLVM is not emitting object files itself; LLVM doesn't emit objects for MSP430 as of this writing. Furthermore, binutils will be required for the foreseeable future for the linker.


The current command to build is: xargo build --release --target=msp430-none-elf. This command has changed over time, so I provide a Makefile as well: make to build, and make prog to program using a Launchpad, mspdebug, and Spy-Bi-Wire connections.

Dependencies Caveats

Compiler/Dependency Mismatches

As Rust the language evolves, certain features in nightly may be enabled which break old commits that once compiled. For example, a ThinLTO bug in rustc ensured compilation for targets using an external assembler- including MSP430- was broken in nightly from August until January!

I can give approximate ranges for which nightlies work with which range of commits, but because the functionality of the nightly I make no guarantees that previous commits will compile; using the correct compiler may not solve all dependency version mismatches in libraries whose public APIs are in flux

That said, it was my intent when porting the code to Rust that tagged commits should be able to serve as an example of how to write bare-metal Rust applications using a variety of different code structures and varying number of external dependencies (see Previous versions should still be able to compile/function with a small to moderate amount of work (see "data layout" in Tags/Comparing Versions for an example).


The most up-to-date version of the firmware uses the Real Time For The Masses (RTFM) Framework. RTFM has underwent various syntax changes for both the Cortex M and MSP430 variants. However, due to space concerns with the most up-to-date version of the MSP430 RTFM implementation, AT2XT opts to use an earlier syntax of RTFM. Using up-to-date RTFM syntax/features is pending improvements in LLVM to convert runtime checks into compile time checks that thus do not take up space in the final binary. To avoid dependency problems for the time being, the variant of RTFM used is available here under the at2xt-pin branch.

Tags/Comparing Versions

Tags to previous versions are included to compare the overhead of adding various abstractions and making the source code look more like an idiomatic hosted Rust program. Some considerations when comparing versions:

  • The MSP430 data layout changed between the time I started writing this firmware (June 12, 2017) and as of this writing (July 16, 2017). Recent nightly compilers will crash with custom provided layout up until commit c85088c. The data layout in msp430.json before this commit should be: e-m:e-p:16:16-i32:16-i64:16-f32:16-f64:16-a:8-n8:16-S16.

  • MSP430 became a supported target within Rust nightly in July 2017, and the target "triple" changed from msp430 to msp430-none-elf. I switched to the internal target as of commit c0dc9b9, but the immediate commit prior c85088c shows how to generate an equivalent binary with the originally-used custom target.

Legacy Source

For comparison purposes, I have kept the old C-based source code as well under the legacy-src directory.

Currently, it is up to the user to set up their toolchain to compile the files for programming an MSP430G2211 or compatible 14-pin DIP MSP430. I recommend the former, if only because MSP430 is already overkill for this project and G2211 is a low-end model :P. However, I . When the C source was written, TI expected users to compile with Code Composer Studio (CCS). Today, a Makefile generic to all OSes and requiring only a command line should work, and will be available soon. Compile using -O2 or better.

The C source code itself should be easy to port to other microcontrollers, except for the use of a __delay_cycles() intrinsic. I had no choice here, as using the timer for a software delay can lock the keyboard FSM to a single state.


Schematics are provided in DIPTrace ASCII format. PCB is provided using Gerber Files and an N/C Drill File.

It is my intention sometime soon to redo the schematic using KiCAD.