Once configuration is complete, the host requests that the tool makes a connection to the target by calling the “activate physical” command. In many interfaces, the physical can be disabled by default or overridden by user code, which implies that an external reset sequence must be applied in order to gain access. In other cases, the external reset must not be used, for example when attaching to a running process. The use of external reset must be specified in the command parameter.
Activating the physical must be followed by device ID validation, to ensure that the session is capable of starting with the device that is expected. For this reason, the activation command returns an ID packet containing the device ID of the target, as read directly from the target. If no valid device is detected, the command will return FAILED.
The GET_ID command can also be used to retrieve this value at any stage during the session. It is read out on demand and not cached.
On completion of a session, the physical must be deactivated. The tool disconnects from the target at this point. In order to re-connect, the physical must be activated again.