AT-to-XT Keyboard Protocol Converter

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.

Prerequisites

This source requires the Rust nightly compiler for the foreseeable future due to the use of abi_msp430_interrupt feature. 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. Alternatively, if you only want to use the nightly compiler for this project, you can run rustup override set --path /path/to/AT2XT/root nightly. This tells rustup to use the nightly compiler by default when compiling the AT2XT crate.

3. Obtain msp430-elf-gcc from TI at the bottom of this page, and make sure the toolchain's bin directory is visible to Rust. Until LLVM gets linker support for msp430, binutils is required for the linker.

Building

MSP430 needs a libcore installed that doesn't conflict w/ your host. The unstable cargo feature -Zbuild-std=core allows a developer to maintain multiple libcores for multiple archs simultaneously.

The current command to build is: cargo build --release -Zbuild-std=core --target=msp430-none-elf. This command has changed over time, so I provide a Justfile as well. Run just --list for a list of avilable recipes. The build can be further customized by setting the following variables on the just command line (e.g. just MODE=release):

• MODE: release or debug. Defaults to release, which must be paired with the --release option to cargo.
• CFLAGS: Flags to pass to cargo. Defaults to --release -Zbuild-std=core --target=msp430-none-elf; the -Zbuild-std=core and --target=msp430-none-elf flags are unconditionally required, but --release should be unset if doing a debug build.

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 CHANGELOG.md). 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).

RTFM

AT2XT at present does not use RTFM framework. This will likely be a version 4.x milestone. 3.x is dedicated to testing the take-based Peripherals API.

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, I provide a generic Makefile instead. To compile, invoke make; there is only a single target, at2xt.elf. This requires the msp430-elf-gcc toolchain from the Prerequisites section.

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.

XTATKEY.ASM

One of the original XT to AT keyboard converters was written by Chuck Guzis in 2009. By my own admission, PIC is a better fit for this project due to 5V compatibility and fewer parts required. However, I wrote my version in 2013 because of my familiarity with msp430, easy 5V interfacing and easy access to parts and an msp430 programmer. In contrast, PIC programmers at the time were expensive (less true today), and I didn't feel like buying or making one.

However, since I've used Chuck(G)'s version as inspiration when I got stuck, I have provided the source and schematics to his version- with permission- under the legacy-src/XTATKEY directory. See linked forum posts for details.

Schematics

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.