Table of Contents
Advertisement
22.3.4
Branch Trace Message Operation
22.3.4.1 BTM Capture and Encoding Algorithm
BTM is accomplished by capturing instruction fetch information from the U-bus and
instruction execution information from the RCPU (VF and VFLS signals), and combining
them to generate program trace messages.
22.3.4.2 Instruction Fetch Snooping
Instruction fetches are snooped on the U-bus. There is a one-to-one correspondence
between instruction fetches marked with the U-bus program trace attribute and the
indication of RCPU VF signal (only 3, 4, 5, and 6) between two synchronization events.
Since U-bus program trace attribute occurs after the indication of VF, it is latched and
paired with the nearest (previous) unpaired VF (3, 4, 5, and 6) indication to determine the
instruction address.
For all other VF indications, except 3, 4, 5, and 6, it is not possible to determine the
instruction address.
22.3.4.3 Instruction Execution Tracking
Instruction execution tracking is performed by capturing the RCPU VF and VFLS signals,
and decoding them to infer the state of the processor. The RCPU VF signals indicate two
classifications of information:
• The current instruction type which is being loaded into the RCPU instruction queue.
For further details refer to the RCPU Reference Manual.
• The number of instructions which are currently being flushed from the RCPU
instruction queue. For further details refer to the RCPU Reference Manual.
22.3.4.4 Instruction Flush Cases
The various conditions under which the RCPU may signal instruction flushes of the RCPU
prefetch queue or RCPU history buffer are:
1. A taken branch (direct, indirect, interrupt or exception) will cause the instruction
prefetch queue (which contains instructions from the now old stream) to be flushed,
and fetching will start from the branch target stream. The sequential instruction
count will be updated to reflect this
2. A mispredicted branch will cause instructions fetched from the new stream to be
flushed, and fetching will resume from the old stream. It will also require a
program trace message to be cancelled and the trace to be corrected.
3. An exception can cause cancellation of multiple taken branches which may require
cancelling multiple program trace messages.
MOTOROLA
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
.
Chapter 22. READI Module
Program Trace
22-51
Advertisement
Table of Contents
