To activate a subsystem is
to make it operational by requesting (using XPm_RequestNode) all its pre-allocation devices. This is an essential
one-time operation that is required before the subsystem image can start execution.
Every time a subsystem is restarted/shutdown, activation happens before execution of the
new subsystem image.
When the application binaries (ELFs) are downloaded using Programmable Device Image (PDI) as a subsystem image, the PLM automatically activates the corresponding subsystem image using the subsystem image ID that is present in the BIF. Currently, this is the default subsystem as there is no support for custom subsystems. However, there can be debugging use-cases where you need to download and execute application binaries (ELFs) directly on a master using the XSDB, and not through the PDI-flow. In such cases, the PLM is not aware of the corresponding subsystem image ID for ELFs. As a result, pre-allocation devices essential for a subsystem to be operational will not be requested, which may cause unforeseen issues. Therefore, before downloading any application binaries (ELFs) using XSDB, a one-time activation of a subsystem is required.
Currently, XSDB automatically requests the PLM to activate the default subsystem before downloading an application binary/ELF on a specific master. In future, when there are multiple/custom subsystems, you may need to explicitly activate the subsystem of choice for such debugging use-cases.