22ba9456de
This patch adds a way to simplify using an external tool to measure timer behaviour on Zephyr. It modifies the timer behaviour jitter_drift.c tests to toggle a GPIO pin (defined via a new DTS compatible, "test-kernel-timer-behavior-external") that can be connected to an external tool, such as a logic analyzer, to measure timer behaviour. This GPIO pin toggle is behind a new CONFIG_TIMER_EXTERNAL_TEST Kconfig. A new pytest test is added so that it can collect the statistics from the external tool and assert some measurements. To collect statistics from the external tool, one needs to provide a Python module which provides a `run(seconds, config)` method, that will perform the test and return the statistics. Check the README file for more information about this interface. Finally, this on twister, this new test is behind a new fixture, "gpio-timerout". Signed-off-by: Ederson de Souza <ederson.desouza@intel.com> Signed-off-by: Tom Burdick <thomas.burdick@intel.com>
72 lines
3.1 KiB
Plaintext
72 lines
3.1 KiB
Plaintext
# Test a timer implementations variance and long term drift
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Records and calculates statistical values against a timer validating that.
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1. Timer variance and standard deviation is below defined acceptable values.
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2. Periodic timers do not drift in either direction from expected total time.
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Timers are meant to be precise and accurate. This test validates an implementation is both.
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External tool testing
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It's also possible to use an external tool, such as a logic analyzer, to
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collect samples. The "kernel.timer.timer_behavior_external" test will toggle a
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GPIO pin on every cycle - first cycle will be a rising edge. This test expects
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a Python module to interface with the external tool, which will provide the
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necessary statistics that the test will use to assert the test status.
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GPIO pin
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To enable external tool testing on a board, it must provide the compatible
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"test-kernel-timer-behavior-external", with property "timeout-gpios" being the
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GPIO pin that will be toggled each period.
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External tool interface
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In order to get data from the external tool, the test expects a Python module,
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named on testcase.yaml, with the following interface:
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run(seconds: float, options: str) -> {}
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The `seconds` parameter defines for how long the data collection is expected
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to run; `options` is a string defined on testcase.yaml with options known to
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the external tool helper module. It should return a dictionary with the
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following statistics, in seconds:
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'mean': Mean time of each period
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'stddev': Standard deviation from the mean time
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'var': Variance from the mean time
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'min': Minimum period registered
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'max': Maximum period registered
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'total_time': Total time, between first and last period.
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Note that the collection may need to go a bit after the "seconds" parameter,
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to account for expected drift in the test and between the DUT and the external
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tool.
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Twister
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For Twister execute the external tool testing, the fixture "gpio_timerout"
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must be available on the device. Also, testcase.yaml
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"harness_config/pytest_args" from "kernel.timer.timer_behavior_external" must
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have parameters "tool", with the name of a loadable Python module and
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"tool-options", a string with options passed to the Python module helper.
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Configuration options
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At its heart, the external testing is actually comparing two clocks: one on
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the board under test and one at the external tool (Zephyr implementation of
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the timer also plays a role, and it's the real target of the test, but it
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depends on the board's clock). Different clocks run at different speeds, so
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they tend to drift. To be able to account for this drift, the external test
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doesn't reuse CONFIG_TIMER_TEST_MAX_DRIFT and
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CONFIG_TIMER_TEST_PERIOD_MAX_DRIFT_PERCENT, instead introducing
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CONFIG_TIMER_EXTERNAL_TEST_MAX_DRIFT_PPM and
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CONFIG_TIMER_EXTERNAL_TEST_PERIOD_MAX_DRIFT_PPM, that can be more finely tuned
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for the hardware in question.
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Also, CONFIG_TIMER_EXTERNAL_TEST_SYNC_DELAY is used to set a delay before a
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test cycle starts, so that the external tool can be set up.
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