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In this topic:

•ITM Stimuli

 

 

Introduction

The Instrumentation Trace Macrocell (ITM) is an optional IP block found in specific Cortex-M implementations. Typically, Cortex-M3, M4, and M7 devices include the ITM, whereas Cortex-M0 and M0+ do not. The ITM serves as an application-driven trace source, supporting printf() style debugging to trace operating system and application events.

 

The ITM can emit trace messages generated by various trace sources:

•Software Trace: Application software writes data directly to the ITM stimulus registers. These trace messages are captured by the BlueBox and interpreted and visualized by winIDEA.

•Hardware Trace: The Data Watchpoint Trace (DWT) generates trace messages that the ITM outputs.

•Time Stamping: Time stamps are generated relative to the trace messages.

•Global System Timestamping: Time stamps can optionally be generated using a system-wide 48-bit count value.

 

 

 

The Trace Port Interface Unit (TPIU) outputs packets to an external debugger (such as the BlueBox) through either the Single Wire Output (SWO) or the 4-bit Parallel trace port. The ITM module enables software instrumentation in the target application by having the application write specific values into a series of ITM stimulus port registers, which causes trace messages to be output over the trace port. winIDEA displays the ITM output in either the Trace window or the Terminal window.

 

The ITM, along with the DWT, is typically featured on Cortex-M devices and can generate timestamp messages within the trace stream. These timestamps provide information on the timing of event generation in relation to their visibility at a trace output port. A local timestamp packet encodes timestamp information for generic control and synchronization, based on a timestamp counter in the ITM. The local timestamp counter can be clocked via synchronous or asynchronous clocking, depending on the device capabilities.

 

The configuration of the ITM module is located in the Trigger Configuration dialog.

 

 

Enable - Global enable bit for the ITM component. Check the box to enable ITM and generate trace messages

 

Timestamps

Local - Enable and set:

•Source > Sync - Timestamp counter uses the processor system clock. Counter increments on each core clock cycle. No prescaling is available in this mode.

•Source > ASync > Prescaler None - Timestamp counter uses asynchronous clock from the TPIU interface. The clock is connected through configurable Prescaler.

•Source > ASync > Select Prescaler - Configurable Prescaler for clock when using asynchronous source.

 

Global > Generate - Enable and defines how often the ITM generates a global timestamp, based on the global timestamp clock frequency.

Note: Device might not implement support for global timestamping.

 

Record Stimuli

Configure enabled stimulus registers that will generate trace messages. Depending on the ITM implementation in the target device, not all stimulus registers might be available.

 

 

ITM Stimuli

 

Enable ITM timestamps  - Configure the CPU to generate ITM timestamp messages.

Timestamp Source - Use ITM generated timestamps as main analyzer time source. This option is intended to be used together with on-chip trace buffer (OCTB / SWO trace), where timestamps would otherwise not be available.

Do not enable this option when parallel trace is being used. When disabled, winIDEA will use the debugger's internal timestamp (which is only possible when parallel trace is being used). For more information check ARM reference manual.

 

In the Trace window the stimulus register ID is shown in Address column and data written to it in Data column. Click Trace button to open the Trace window.