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MPC565/MPC566 Reference Manual
MOTOROLA
Application Notes
23.12.3.2 Read/Write Access
In case the throughput requirements for block data traces are not acceptable, read/write
access should be used to load the variables from the calibration memory.
Option A: Block Read Access
This method calls for setting aside some memory (~ 1-Kbyte RAM locations) for
calibration variable measurement. When the software tasks that modify the variables are
completed, they will copy the variables into contiguous locations in this reserved space.
Then the tasks will indicate to the external tool that the variables are valid by any of various
means (write keyword to special address, watchpoint etc.). The calibration tool will then
proceed to read the variables corresponding to the channel completed using the block read
access feature.
This method may be more preferable because it is more likely to be synchronized and
coherent data for multiple task scenarios.
The disadvantage of using block read access is the impact it has on RCPU performance.
Block word read accesses can be done on the L-bus every 13 clocks. If the block word read
accesses happen to be overlapped with a block access via the RCPU, the maximum
intrusion will be 7.7%.
Option B: Single Read Access
Single read accesses can also be used to acquire calibration variables which are not located
in contiguous memory locations.
Single read accesses also have an the impact on RCPU performance. Single word read
accesses can be done on the L-bus every 74 clocks. If single word read accesses happen to
be overlapped with a block access via the RCPU, the maximum intrusion will be 1.3%. This
is significantly better when compared to block read accesses (7.7%).
The disadvantage of using single read access the data trace throughput. For single read
accesses, 0.41 million words can be messaged out via the READI port, whereas for block
read accesses, approximately 4 million words can be messaged out via the READI port.
23.12.3.3 Calibration Constant Tuning
Calibration constant tuning refers to the third basic requirement for automotive
development tools. READI supports calibration constant tuning via the read/write access
feature.
The read/write access protocol provides run-time access to MCU registers and memory
map. READI implements the run-time read/write access feature via two MDI pins and eight
MDO pins or one MDI pin and two MDO pins.