Nexus3/ Module
e200z3 Power Architecture Core Reference Manual, Rev. 2
Freescale Semiconductor
10-23
2. The second pass through the DR then shifts the data in or out of the JTAG port, least significant bit
first.
a) During a read access, data is latched from the selected Nexus register when the JTAG state
machine passes through the capture-DR state.
b) During a write access, data is latched into the selected Nexus register when the JTAG state
machine passes through the update-DR state.
10.6
Ownership Trace
This section details the ownership trace features of the Nexus3/ module.
10.6.1
Overview
Ownership trace provides a macroscopic view, such as task flow reconstruction, when debugging software
is written in a high-level or object-oriented language. It offers the highest level of abstraction for tracking
operating system software execution. This is especially useful when the developer is not interested in
debugging at lower levels.
10.6.2
Ownership Trace Messaging (OTM)
Ownership trace information is messaged by means of the auxiliary port using OTM. For e200z3
processors, there are two distinct methods for providing task/process ID data. Some e200 processors
contain a Book E–defined process ID register within the CPU while others may not. Within Nexus,
task/process ID data is handled in one of the following two ways in order to maintain IEEE-ISTO 5001
compliance.
1. If the process ID register exists, it is updated by the operating system software to provide
task/process ID information. The contents of this register are replicated on the pins of the processor
and connected to Nexus. The process ID register value can be accessed using the mfspr/mtspr
instructions. See
Section 2.16.5, “Process ID Register (PID0).”
2. If the process ID register does not exist, the user base address register (UBA) is implemented
within Nexus. The UBA can be accessed by means of the JTAG/OnCE port and contains the
address of the ownership trace register (OTR). The memory-mapped OTR is updated by the
operating system software to provide task/process ID information.
NOTE
The e200z3 includes a process ID register (PID0), thus the UBA
functionality is not implemented.
There are two conditions that cause an ownership trace message:
1. When new information is updated in the OTR register or process ID register by the e200z3
processor, the data is latched within Nexus and is messaged out through the auxiliary port, allowing
development tools to trace ownership flow.
2. When the periodic OTM message counter expires after 255 queued messages without an OTM, an
OTM is sent. The data is sent from either the latched OTR data or the latched process ID data. This
allows processors using virtual memory to be regularly updated with the latest process ID.