Multidrop serial wire debug (SWD) allows simultaneous access to an unlimited number of devices through a single connection. This is useful for connectivity-constrained products that have several chips with multidrop support.
To select a target in a multidrop capable product, the debugger must write the correct TPARTNO, and TDESIGNER fields into the SW-DP TARGETSEL register. Values for these fields are located in DLPIDR.
For more information about multidrop SWD, see the Arm Debug Interface Architecture Specification, ADIv5.0 to ADIv5.2.