3.6.2. Single-processor tracing

Some chips might not dedicate 16 pins to the TRACEPKT bus. Under some circumstances you might be able to reuse miscellaneous output signals from the chip as trace port pins. To allow this the ETM7 has the following outputs:

Figure 3.13 shows one way in which the TRACEPKT pins can be shared with the ASIC pins.

Figure 3.13. Reusing TRACEPKT pins

You can use the PORTSIZE and ETMEN signals to control on-chip logic to select between the normal ASIC output signals and the ETM7 trace port signals. This allows you to control the port width of the trace, and the number of pins used, from the debugger.

At reset the ETM7 is disabled (ETMEN LOW) and a 4-bit port is selected (PORTSIZE = 000). This ensures that normal operation of the ASIC is undisturbed.

Once the debug session starts, the debug tools can control ETMEN and PORTSIZE by programming the ETM control register.

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