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22.4.7
Data Trace Queuing
For queuing program trace, data trace, and ownership trace messages, READI implements
a queue 32 messages deep (The queue is 16 messages deep on some versions; refer to
device errata). Messages that enter the queue are transmitted via the output auxiliary port
in the order in which they are queued.
If multiple trace messages need to be queued at the same time,
program trace messages have a higher priority for queue entry
than data trace messages, unless the data trace buffers are full,
in which case the data trace messages are given temporary
higher priority than the program trace messages.
22.4.8
Throughput and Latency
22.4.8.1 Assumptions for Throughput Analysis
• All accesses are data trace only
• Output signals are always free (not in middle of transmission) when requested
• Relative Address field for data trace messages is 20 bits
• Data field for data trace messages is 32 bits
• One idle clock between data trace messages
22.4.8.2 Throughput Calculations
The data (read or write) trace message is 58 bits (6 [TCODE] + 20 [Relative address] + 32
[Data]).
Data trace messages are transmitted out via the MDO signals. Hence it will take eight
clocks (58 bits/8 MDO signals) to send a message. There will be one idle clock before the
next data trace message can be sent.
Therefore, the average number of data trace messages that can be transmitted out is 6.2
million (1/161ns) per second, or 24.8 million bytes of read/write data per second.
MOTOROLA
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
NOTE
Chapter 22. READI Module
Data Trace
22-61
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