Nexus3/ Module
e200z3 Power Architecture Core Reference Manual, Rev. 2
10-38
Freescale Semiconductor
Exception conditions that result in data trace synchronization are summarized in
.
10.8.3
DTM Operation
10.8.3.1
DTM Queueing
Nexus3/ implements a programmable depth queue (a minimum of 32 entries is recommended)
for queuing all messages. Messages that enter the queue are transmitted through the auxiliary pins in the
order in which they are queued.
NOTE
If multiple trace messages need to be queued simultaneously, watchpoint
messages have the highest priority:
WPM
→
OTM
→
BTM
→
DTM. Up to two messages may be
simultaneously queued.
Table 10-25. Data Trace Exception Summary
Exception Condition
Exception Handling
System reset negation
At the negation of JTAG reset (
j_trst_b), queue pointers, counters, state machines,
and registers within the Nexus3/ module are reset. If data trace is
enabled, the first data trace message is a data write/read with synchronization
message.
Data trace enabled
The first data trace message (after data trace has been enabled) is a
synchronization message.
Exit from low power/debug
Upon exit from a low-power mode or debug mode, the next data trace message is
converted to a data write/read with synchronization message.
Queue overrun
An error message occurs when a new message cannot be queued due to the
message queue being full. The FIFO discards messages until it has completely
emptied the queue. Once emptied, an error message is queued. The error
encoding indicates which type(s) of messages attempted to be queued while the
FIFO was being emptied. The next DTM message in the queue will be a data
write/read with synchronization message.
Periodic data trace
synchronization
A forced synchronization occurs periodically after 255 data trace messages have
been queued. A data write/read with synchronization message is queued. The
periodic data trace message counter then resets.
Event in
If the Nexus module is enabled, a
nex_evti_b assertion initiates a data trace
write/read with synchronization message upon the next data write/read (if data
trace is enabled and the EIC bits of the DC1 register have enabled this feature).
Attempted access to secure
memory
For SOCs that implement security, any attempted read or write to secure memory
locations temporarily disables data trace and causes the corresponding DTM to be
lost. A subsequent read/write queues a data trace read/write with a
synchronization message.
Collision priority
All messages have the following priority: WPM
→
OTM
→
BTM
→
DTM. A DTM
message that attempts to enter the queue at the same time as a watchpoint
message or ownership trace message or branch trace message will be lost. A
subsequent read/write queues a data trace read/write with a synchronization
message.