121 lines
4.0 KiB
ReStructuredText
121 lines
4.0 KiB
ReStructuredText
.. _emulators:
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Peripheral and Hardware Emulators
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#################################
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Overview
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========
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Zephyr supports a simple emulator framework to support testing of drivers
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without requiring real hardware.
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Emulators are used to emulate hardware devices, to support testing of
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various subsystems. For example, it is possible to write an emulator
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for an I2C compass such that it appears on the I2C bus and can be used
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just like a real hardware device.
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Emulators often implement special features for testing. For example a
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compass may support returning bogus data if the I2C bus speed is too
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high, or may return invalid measurements if calibration has not yet
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been completed. This allows for testing that high-level code can
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handle these situations correctly. Test coverage can therefore
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approach 100% if all failure conditions are emulated.
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Concept
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=======
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The diagram below shows application code / high-level tests at the top.
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This is the ultimate application we want to run.
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.. figure:: img/arch.png
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:align: center
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:alt: Emulator architecture showing tests, emulators and drivers
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Below that are peripheral drivers, such as the AT24 EEPROM driver. We can test
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peripheral drivers using an emulation driver connected via a native_posix I2C
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controller/emulator which passes I2C traffic from the AT24 driver to the AT24
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simulator.
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Separately we can test the STM32 and NXP I2C drivers on real hardware using API
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tests. These require some sort of device attached to the bus, but with this, we
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can validate much of the driver functionality.
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Putting the two together, we can test the application and peripheral code
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entirely on native_posix. Since we know that the I2C driver on the real hardware
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works, we should expect the application and peripheral drivers to work on the
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real hardware also.
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Using the above framework we can test an entire application (e.g. Embedded
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Controller) on native_posix using emulators for all non-chip drivers:
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.. figure:: img/app.png
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:align: center
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:alt: Example system, using emulators to implement a PC EC
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The 'real' code is shown in green. The Zephyr emulation-framework code is shown
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in yellow. The blue boxes are the extra code we have to write to emulate the
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peripherals.
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With this approach we can:
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* Write individual tests for each driver (green), covering all failure modes,
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error conditions, etc.
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* Ensure 100% test coverage for drivers (green)
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* Write tests for combinations of drivers, such as GPIOs provided by an I2C GPIO
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expander driver talking over an I2C bus, with the GPIOs controlling a charger.
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All of this can work in the emulated environment or on real hardware.
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* Write a complex application that ties together all of these pieces and runs on
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native_posix. We can develop on a host, use source-level debugging, etc.
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* Transfer the application to any board which provides the required features
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(e.g. I2C, enough GPIOs), by adding Kconfig and devicetree fragments.
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Available emulators
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===================
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Zephyr includes the following emulators:
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* EEPROM, which uses a file as the EEPROM contents
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* I2C emulator driver, allowing drivers to be connected to an emulator so that
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tests can be performed without access to the real hardware
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* SPI emulator driver, which does the same for SPI
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* eSPI emulator driver, which does the same for eSPI. The emulator is being
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developed to support more functionalities.
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* CAN loopback driver
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A GPIO emulator is planned but is not yet complete.
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Samples
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=======
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Here are some examples present in Zephyr:
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#. Bosch BMI160 sensor driver connected via both I2C and SPI to an emulator:
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.. zephyr-app-commands::
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:app: tests/drivers/sensor/accel/
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:board: native_posix
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:goals: build
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#. Simple test of the EEPROM emulator:
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.. zephyr-app-commands::
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:app: tests/drivers/eeprom
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:board: native_posix
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:goals: build
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#. The same test has a second EEPROM which is an Atmel AT24 EEPROM driver
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connected via I2C an emulator:
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.. zephyr-app-commands::
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:app: tests/drivers/eeprom
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:board: native_posix
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:goals: build
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