hootswitch

Hootswitch is a prototype ADB multiplexer that allows peripherals (inluding keyboards and mice) to be shared across up to four retro computers.

This project has two parts: an example hardware design and the firmware, located in their respective folders in this repo.

Status

Basic ADB keyboards and mice are supported. Switching between computers works via the button on the front or Control / Option / ⌘ / Shift in sequence, followed by 1 - 4 to choose a port.

The firmware is still under active development and many bugs remain. Other types of ADB devices are not supported yet. No features based on the Pico W wireless chip have not been implemented at this point.

This section will continue to be updated as progress is (hopefully) made.

Building

You will need the Pico SDK and associated tooling. There is a setup script here that assumes you're using a Raspberry Pi as your development environment if you want to try that; I personally use Debian bookworm on a regular x86 system instead, set up as follows.

Dependencies and associated tools:

sudo apt install git cmake gcc-arm-none-eabi gcc gdb-multiarch automake \
    autoconf build-essential texinfo libtool libftdi-dev libusb-1.0-0-dev \
    openocd

Clone the Pico SDK. Execute git submodule update --init in that project to get sub-libraries added. Set PICO_SDK_PATH to point at where the SDK lives via ~/.bashrc or equivalent; something like export PICO_SDK_PATH=/home/saybur/src/pico-sdk would be suitable after being adjusted for your environment.

Also clone or download FreeRTOS. The LTS release is likely fine. Set FREERTOS_KERNEL_PATH to the folder where FreeRTOS-Kernel is located via the above method.

Once you have everything set up, build as follows from the root of the repo.

mkdir -p build
cd build
cmake ../firmware
make

Among other files, this will produce hootswitch.uf2. Make sure your power selection is correct, then hold down the BOOTSEL button while you plug in to your computer via USB. Copy the .uf2 onto the new mass storage device. Reboot.

Debugging

You will want to invoke cmake with -DCMAKE_BUILD_TYPE=Debug.

The official debugger is dirt cheap and works reasonably well if you plan to develop on the firmware. It can be used as follows to upload without needing to fuss with the BOOTSEL button. Be in the dialout group to avoid needing sudo all over the place. OpenOCD can be started as follows.

openocd -c "set USE_CORE 0" -f interface/cmsis-dap.cfg -f target/rp2040.cfg \
    -c "adapter speed 5000" -c "rp2040.core0 configure -rtos FreeRTOS"

See https://github.com/raspberrypi/pico-sdk/issues/1622 for a discussion about USE_CORE 0 above. The above is fine for now with the current state of development, which runs only on a single core anyway.

In another terminal, run gdb-multiarch hootswitch.elf. Connect to the device with target remote localhost:3333 (or automate this step via ~/.gdbinit). See the documentation for specifics; the following commands are likely useful (with the caveat that I am most definitely not an authority on gdb):

• load will update programming with the current ELF.
• monitor reset init will restart and halt for instructions.
• print X prints information about something, including variables.
• br X adds a breakpoint at X, del removes one or more.
• continue will proceed, stopping at breakpoints; Ctrl-C halts.
• finish completes a function.
• bt prints a backtrace, bt f prints a backtrace with symbols.
• up and down moves around the frames of a call.
• i r prints registers.
• p X prints variable X.
• p/x *0x0 prints in hex from the address, useful for peripheral registers.
• i threads prints information relevant to FreeRTOS thread execution.

Licenses

Except where otherwise noted, all software is available under the GNU GPL v3. The example hardware is available under the CERN Open Hardware Licence strongly-reciprocal variant, version 2. Refer to the licenses for specific terms.