ToolStick
Description
For initial programming of the DSerial bootloader a programming cable is needed. Also it's nice to have for in-circuit debugging of microcontroller programs.
ToolStick is an extremely cheap (about USD 11) evaluation platform by Silicon Laboratories. It's not originally meant to be a generic programming cable for the SiLabs C2 interface, but can be easily modified into a fully-functional one.
See self-explanatory pictures of the modification below. The connector is made out of a 2x4 header and slides onto DSerial PROG connector.