Specifications

Cortex-M3 / Cortex-M3 with ETM (AT420/AT425)

Date of Issue: 12-Nov-2008 ARM Errata Notice Document Revision 2.0

PR326-PRDC-009450 v2.0

Non Confidential

429965: Trigger packets sometimes not inserted in trace stream

Status

Affects: product Cortex-M3 with ETM.

Fault status: Cat 2, Present in: r0p0,r1p0,r1p1,r1p1-00rel0, Fixed in r1p1-01rel0.

Description

It is possible to configure a trigger event for the ETM which is used to assist with trace capture and the

subsequent analysis of trace by the user. The trigger condition is indicated by a pulse on the ETMTRIGOUT

signal, and is also inserted in the trace stream using a special packet.

If a trigger condition occurs when there is no data in the ETM's FIFO and there are no instructions yet to be

traced, the ETMTRIGOUT signal is pulsed correctly, but the trigger packet is not inserted in the trace stream.

Conditions

1. The ETM is enabled

2. The trace FIFO is empty

3. There are no instructions already executed but not yet entered in the trace fifo.

Implications

This erratum only affects the trace stream which is generated by the ETM. There is no impact on the normal

processing operation of the core.

This erratum only affects the inclusion of the trigger packet in the trace stream. It does not affect the visibility of

the trigger condition through the ETM's programmers model (bit 2 of the ETM Status Register, register 4).

It does not affect the indication of the trigger condition to the trace capture device, and a formatter trigger packet

will be inserted if enabled.

The erratum does not occur if a trigger is generated using DWT to detect an instruction address if Trace Enable

is high.

When this erratum occurs, the user will not be able to determine the location in the executed instruction

sequence at which the trigger condition occurred. Due to the conditions which are required for this erratum to

occur, it is more likely that the erratum occurs when an external input is being used to generate the trigger

condition.

Workaround

There is no workaround to force the trigger packet to be included in the trace stream. If using the CoreSight

formatter protocol, e.g. TPIU/ETB with trigger embedded, then the position of the embedded trigger can be

used, however the location of the embedded trigger is approximate.