2 posts tagged with "Testing"

In the article about unit testing with Unity and CMock I said that the tests on the PC do not find "the differences between the PC and the MCU". This article is about those differences, and about the tool that finds them: a simulator that runs the real binary. Not the logic compiled for the PC, but the very .elf that the ARM compiler made, with the real startup code and the real linker script, on a model of a processor and its peripherals.

I will show two experiments that I ran: the same test source that passes on the PC and fails on the Cortex-M4, and a firmware that writes to the registers of a USART at the real addresses of an STM32F4 and whose text appears in the terminal. At the end there is an honest list of what a simulator will not tell you.

"Embedded software cannot be unit tested, you need the hardware." I hear it often, and it is true for exactly one kind of code: the code that touches the registers. All the rest, the state machines, the protocol parsers, the control logic, the conversion of the values, is plain C that compiles on your PC. And on your PC it runs in milliseconds, without a debugger, without a cable and without flashing.

This article shows how to test a module with Unity (the test framework) and CMock (the generator of mocks), from the design that makes it possible to the CMake file that builds it. Everything was built and run, and the output below is the real one.