Debug support (DBG) RM0440
2098/2126 RM0440 Rev 4
47.15 ETM (Embedded Trace Macrocell™)
47.15.1 General description
The ETM enables the reconstruction of program execution. Data are traced using the Data
Watchpoint and Trace (DWT) component or the Instruction Trace Macrocell (ITM) whereas
instructions are traced using the Embedded Trace Macrocell (ETM).
The ETM transmits information as packets and is triggered by embedded resources. These
resources must be programmed independently and the trigger source is selected using the
Trigger Event Register (0xE0041008). An event could be a simple event (address match
from an address comparator) or a logic equation between 2 events. The trigger source is
one of the four comparators of the DWT module, The following events can be monitored:
• Clock cycle matching
• Data address matching
For more informations on the trigger resources refer to Section 47.13: DWT (data
watchpoint trigger).
The packets transmitted by the ETM are output to the TPIU (Trace Port Interface Unit). The
formatter of the TPIU adds some extra packets (refer to Section 47.17: TPIU (trace port
interface unit)) and then outputs the complete packet sequence to the debugger host.
47.15.2 Signal protocol, packet types
This part is described in the section 7 ETMv3 Signal Protocol of the Arm
®
IHI 0014N
document.
47.15.3 Main ETM registers
For more information on registers refer to the chapter 3 of the Arm
®
IHI 0014N specification.
Table 441. Main ETM registers
Address Register Details
0xE0041FB0 ETM Lock Access
Write 0xC5ACCE55 to unlock the write access to the
other ETM registers.
0xE0041000 ETM Control
This register controls the general operation of the ETM,
for instance how tracing is enabled.
0xE0041010 ETM Status
This register provides information about the current status
of the trace and trigger logic.
0xE0041008 ETM Trigger Event This register defines the event that controls trigger.
0xE004101C
ETM Trace Enable
Control
This register defines which comparator is selected.
0xE0041020 ETM Trace Enable Event This register defines the trace enabling event.
0xE0041024 ETM Trace Start/Stop
This register defines the traces used by the trigger source
to start and stop the trace, respectively.
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