Understand the Peripheral Complexity
Before diving into mock generation, first ensure that you have a thorough understanding of the hardware peripheral and its associated API. Complex peripherals often involve tight coupling with hardware registers and callbacks, making them a challenge to mock. Document the peripheral's behavior, expected inputs/outputs, and interactions with other components to clarify what needs to be simulated.
Analyze the Header File
Examine the header file of the peripheral's driver to identify the functions and global variables that need to be mocked. CMock generates mocks based on function prototypes found in header files. Complex peripherals might have hardware-specific types or #defines that need attention. Ensure that these are well-documented and dummy alternatives are provided if necessary.
Preprocess the Header
Preprocessing the header file will help identify any macros, inline functions, or conditional compilation that might affect mock generation. Run a preprocessor on your header file to expand these elements, ensuring that CMock does not attempt to mock macros or functions that are irrelevant or not required.
gcc -E your_header_file.h -o preprocessed_header.h
Create Mock Configuration
To facilitate mock generation for complex hardware peripherals, define a customized CMock configuration. This includes setting up CMock's configuration file (:cmock: section in a yml file) to handle specific attributes or calling conventions used by the hardware APIs.
:cmock:
:unity:
:path: ["unity/src"]
:treat_as:
:uint32: ["REGISTER_TYPE"]
:plugins:
- callback
- ignore
- return_value_history
Refactor Complex Functions
If certain peripheral functions encapsulate intricate logic or direct hardware interactions, consider refactoring them into smaller, mockable units or isolating hardware-specific code within static functions. This allows easier mocking of higher-level functions.
Utilize Callback Plugins
For functions interacting with complex peripherals, use CMock’s callback plugins to simulate hardware interactions. Callback plugins can imitate behavior, change outputs based on inputs, or simulate errors. This is crucial for functions that do not normally return values or rely on indirect side effects.
void PeripheralFunction_CMockIgnoreAndReturn(UNITY_LINE_TYPE cmock_line, int call_count);
void PeripheralFunction_CMockStopIgnore(void);
void PeripheralFunction_CMockExpectAndReturn(UNITY_LINE_TYPE cmock_line, RETURN_TYPE cmock_to_return);
void PeripheralFunction_AddCallback(CMOCK_PeripheralFunction_CALLBACK Callback);
Ensure Order of Operations
Complex peripherals often have strict requirements for call order. Utilize CMock’s expectation feature to verify that functions are called in the right sequence and with expected arguments. This ensures that the peripheral is correctly mocked as it would operate in the real environment.
Integrate with a Testing Framework
Combine CMock with a testing framework, like Unity, to verify the interactions with the peripheral. Implement test cases that validate both the happy path and edge cases, including error handling and unusual interactions with the hardware. This will ensure robust and comprehensive testing coverage.
#include "unity.h"
#include "mock_my_peripheral.h"
void setUp(void) {
// Initialization code here
}
void tearDown(void) {
// Cleanup code here
}
void test_PeripheralBehavior(void) {
PeripheralFunction_ExpectAndReturn(0, expected_value);
// Add your test code here
}
Mock for Interrupt Handlers
For peripherals that involve interrupts, mock the interrupt handlers to test how the firmware responds to asynchronous events. This might involve simulating the peripheral's state changes or directly invoking expected callbacks as would happen during an interrupt.
Keep Mock Configuration Updated
As the driver and related APIs evolve, ensure that the mock configuration and test cases are updated to reflect the latest state. Regularly refactor and optimize the mock setup as new features or changes in the API surface emerge.
Leverage Community and Documentation
Finally, consult CMock documentation and community resources if you encounter issues specific to complex peripherals. Community forums, example projects, or the official CMock GitHub may have solutions or workarounds for hardware-related quirks.
