As a developer of medical device it happens that your system shall include different level of software to be used in the system. Usually we refer to common software applications that are used on one of the common used OS such as Windows, Andriod, iOS etc. as one type of software.
When we are programming our chip set and now include a program to be used on that chip set (Hardware) than we refer to this program as Firmware.
So when you intend to write your FwRS please use this work item, and for your detail design your the FwDD.
Traceability now will be clear and process will be easy to manage.