The firmware for the open-source HDMI KVM switch I built. Note that this repository has the code for both the base and the keypad.

There's also some generic STM8 code in the stm8/ folder, which is used to set up and access various peripherals. Finally, there are some shared definitions in the shared/ folder, which are used for the I2C communication between the base and keypad.

Download SDCC (tested with version 4.0) and stm8flash. Ensure that both commands are in your PATH and working, meaning the sdcc and stm8flash commands both do something.

You may want to use my fork of stm8flash, which allows selecting an ST-LINK adapter based on its USB port number. If you don't use it, then you must edit the upload-base.sh and upload-keypad.sh scripts to remove the port number flags (-S port:1 and -S port:3). See the "fork of stm8flash" section, at the end, for more.

You will also need an ST-LINK adapter supported by stm8flash—either an official one or a clone. To test that the adapter and its connection works, you can try to read data from the STM8S003F3, like so: stm8flash -c stlinkv2 -p stm8s003f3 -s flash -r test.bin. If you are not using an stlinkv2 adapter, then you will probably need to edit the upload scripts to change the adapter type passed to stm8flash.

You should connect the ground, nRST, and SWIM pins from the board to your ST-LINK. You can also connect the 3.3V power pin if you want to power the board from your ST-LINK. If you do that, then make sure the board is not otherwise connected to power. Do not connect multiple sources of power at the same time. For the base, this means not plugging in any HDMI cables, as they can backfeed +5V power! The base does have a +5V pin that you can connect to the ST-LINK's +5V rail instead.

If you want to read debug messages, then you should also connect a USB-to-UART adapter to the TX, RX, and GND pins, with the UART set to 8N1 at 57600 baud.

Run the ./build.sh script to build the firmware for both the base and keypad. The final output will be two Intel HEX files, base/main.ihx and keypad/main.ihx. The ./upload-base.sh and ./upload-keypad.sh scripts will upload the respective firmware to a connected STM8S003F3.

For this project, I forked stm8flash to allow selecting an ST-LINK adapter based on its USB port number.

This was done as a slight hack on top of the existing serial number matching code. For example, to select the adapter on port 1, set the serial number port:1. You can use a tool like lsusbtree to see the port numbers.

This was done because some clone ST-LINK adapters do not have a reliable serial number field, and so the port number is used as an alternative form of identifier. If you're using the official ST-LINK adapter, you can just use the serial number.

The instructions to set up the fork are the same as the normal program: ./configure, then make, then sudo make install.