Functional Description
2-4
Copyright © 2002, 2003 ARM Limited. All rights reserved.
ARM DDI 0275D
2.2
Operation
The on-chip ETB11 operates as follows:
1.
The ETM architecture version is supplied to the Data Formatter using the
PROTOCOL[1:0]
signal. This must be set to b10.
2.
Configuration registers are set up through the TAP controller or through the AHB
interface.
3.
Trace capture is enabled using the control register.
4.
Trace data is continuously written into the trace RAM while the ETB11 is enabled
and the trigger counter value is nonzero. Once the ETM11RV indicates a trigger
by asserting
TRIGGER
, the trigger counter decrements once per word of trace
stored.
When the trigger counter reaches zero the acquisition complete flag, AcqComp,
is activated and trace capture stops. The value loaded into the trigger counter
therefore sets the number of data words stored in the trace RAM after a trigger
event.
5.
The debugging tools through the TAP controller can read trace data stored in the
trace RAM through the TAP controller or through the AHB interface.
•
To read data through the TAP controller you must:
1.
Disable trace capture. If trace capture is enabled when the RAM Data
Register is accessed, the RAM value read is incorrect.
2.
Write the location that data is read from into the RAM Read Pointer
Register.
3.
Read the RAM Data Register to return the data at the address stored
in the RAM Read Pointer Register. The read address pointer
increments after each RAM Data Register read and the next data
value is automatically read from the RAM and stored in the RAM
Data Register.
Note
You must precede the read access by a write to the RAM Read Pointer
Register to ensure that the first RAM Read Register access returns
valid data.
•
The trace data can also be read using the AHB interface. The trace RAM is
aliased into the system memory space. This means that reading a value from
the trace RAM requires an
LDR
type instruction from the trace RAM address
space. The AHB interface can also write to the ETB11 memory when trace
capture is disabled.
Summary of Contents for ETB11
Page 6: ...List of Tables vi Copyright 2002 2003 ARM Limited All rights reserved ARM DDI 0275D ...
Page 8: ...List of Figures viii Copyright 2002 2003 ARM Limited All rights reserved ARM DDI 0275D ...
Page 46: ...Functional Description 2 26 Copyright 2002 2003 ARM Limited All rights reserved ARM DDI 0275D ...
Page 70: ...Signal Descriptions A 6 Copyright 2002 2003 ARM Limited All rights reserved ARM DDI 0275D ...
Page 78: ...Glossary Glossary 4 Copyright 2002 2003 ARM Limited All rights reserved ARM DDI 0275D ...