Arm(R) Ethos(TM)-U Monitor
Ethos-U monitor is a library that provides an example of how to extract the values of the PMU registers on the Arm Ethos-U55 NPU during an ongoing inference, using an arbitrary timer source to trigger interrupts at a set interval. It implements two backends, EventRecorder and printf. An example application showing how to use Ethos-U monitor is included.
Usage
When the Ethos-U monitor constructor is called, the user specifies which backend to use, as well as the EventIDs for the EventRecorder entries. In the second step, configure is used to configure which PMU registers that is to be recorded. A list of available PMU registers can be found in pmu_ethosu.h in the core-driver repository. monitorSample is then used to record the values of the registers on the selected backend. Lastly, release disables the PMU.
Functions
| Function name | Description |
|---|---|
EthosUMonitor(eventRecordIds, backend) | eventRecordIds lists the EventIDs that will be associated with the list of PMU registers configured in configure when using EVENT_RECORDER as backend.backend describes which backend to use, and can be either PRINTF or EVENT_RECORDER |
configure(driver, eventIds) | Configures the PMU to monitor the PMU registers listed in eventIds. The maximum number of PMU registers to monitor is 4. |
release(driver) | Disables the PMU. |
monitorSample(driver) | Samples the PMU registers configured in configure and logs them using the selected backend. |
Example
An example on how to use Ethos-U monitor can be found in the baremetal application in the ethosu-core-platform repository.
The functions ethosu_inference_begin and ethosu_inference_end are defined as weak symbols in ethosu_driver.c.
They are called by the Ethos-U driver before and after the Ethos-U custom operator is executed. In the example application a timer source is configured to periodically trigger an interrupt, on which the the configured PMU registers are sampled one by one and recorded using EventRecorder as backend. Note that the events in this example are logged from an interrupt context which will impact the execution time.
Below is a sequence diagram showing a simplified version of how the different components interact.
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Output format
EventRecorder
For each of the configured PMU registers, an event is recorded using the EventRecord2 function. Each event consists of two int32-values and an id.
In the example application, the following PMU registers are recorded: | EventID | Value 1 | Value 2 | | ------- | ------- | ------- | | Id1 | ETHOSU_PMU_CYCLE | Register value | | Id2 | ETHOSU_PMU_NPU_ACTIVE | Register value |
Id1 and Id2 are defined by the eventRecordIds parameter in the constructor of Ethos-U monitor. Value 1 is the PMU register number, as represented by the ethosu_pmu_event_type enum. Value 2 is the value of the PMU register when read by the monitorSample function.
printf
When using printf the register values are printed on the format ethosu_pmu_cntr<counter_no> : <register_value>, where counter_no is the index (0-3) of the configured PMU register, and register_value is the value of the PMU register.