This page documents how the Ring Fit Adventure game uses hidbus for using the Ring-Con ExternalDevice, which attaches to Joy-Cons.
The BusType used with GetBusHandle is value 0 or 1.
The ExternalDeviceId is 0x20. After EnableExternalDevice is used successfully during initialization, EnableJoyPollingReceiveMode(flag=true) is used with 4-byte command 0x020101. For cleanup, DisableJoyPollingReceiveMode is used then on success EnableExternalDevice(flag=false) is used.
Commands (input data for EnableJoyPollingReceiveMode / SendAndReceive) start with the u32 cmd, there's generally no data after that. Data in the replies are at least 0x4-bytes, with fields being 4-byte aligned. Reply+0 is the u8 status. When the output size doesn't match the expected size, or status is non-zero, error 0xEDA is returned. When status is non-zero, a func is called with the status value which updates global state.