7 Debug Transport Module (DTM)
Debug Transport Modules provide access to the DM over one or more transports (e.g. JTAG or USB).
There may be multiple DTMs in a single platform. Ideally every component that communicates with the outside world includes a DTM, allowing a platform to be debugged through every transport it supports. For instance a USB component could include a DTM. This would trivially allow any platform to be debugged over USB. All that is required is that the USB module already in use also has access to the Debug Module Interface.
Using multiple DTMs at the same time is not supported. It is left to the user to ensure this does not happen.
This specification defines a JTAG DTM in Section [sec:jtagdtm]. Additional DTMs may be added in future versions of this specification.
An implementation can be compliant with this specification without implementing any of this section. In that case it must be advertised as conforming to “RISC-V Debug Specification , with custom DTM.” If the JTAG DTM described here is implemented, it must be advertised as conforming to the “RISC-V Debug Specification , with JTAG DTM.”