{"id":1973,"date":"2020-08-29T16:55:04","date_gmt":"2020-08-29T23:55:04","guid":{"rendered":"http:\/\/visualgdb.com\/w\/?p=1973"},"modified":"2020-08-30T15:01:17","modified_gmt":"2020-08-30T22:01:17","slug":"improving-your-embedded-firmware-quality-with-unit-tests","status":"publish","type":"post","link":"https:\/\/visualgdb.com\/tutorials\/tests\/arm\/","title":{"rendered":"Improving your Embedded Firmware Quality with Unit Tests"},"content":{"rendered":"

This tutorial shows how to use VisualGDB to create unit tests for embedded projects that will run directly on the embedded device. Unit tests are supported on the ARM Cortex devices using Segger J-Link or OpenOCD and can be supported on other devices using VisualGDB extension SDK. Before you begin, install VisualGDB 5.2<\/a> or later.<\/p>\n

In this tutorial we will create a simple test project for the STM32F4Discovery board that will verify that the execution time of the sinf()<\/strong> function matches a certain constraint. We will show how switching the FPU mode from hardware to software would instantly cause the test to fail. If your program contains performance-critical code, you can use this approach to separately test the performance of each critical part and catch slowdowns caused by recent changes before they start causing trouble.<\/p>\n

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  1. Begin with starting Visual Studio and selecting File->New Project->VisualGDB->Embedded Project Wizard<\/strong>:\"\"<\/a><\/li>\n
  2. Enter the name and location for your project:\"\"<\/a><\/li>\n
  3. On the first page select Create a new project -> Unit test project -> MSBuild -> TinyEmbeddedTest<\/strong>:\"\"<\/a>VisualGDB also supports CppUTest<\/strong> and GoogleTest<\/strong> frameworks out-of-the-box, so you can use one of those if your device has enough FLASH memory. The TinyEmbeddedTest<\/strong> framework provided by Sysprogs focuses on using as little FLASH space as possible and providing basic CppUTest-compatible API:<\/li>\n
  4. On the next page select the ARM toolchain and choose your device from the device list:\"\"<\/a>Make sure the hardware floating point mode is selected.<\/li>\n
  5. Proceed with the default sample for the test project:\"\"<\/a><\/li>\n
  6. Finally select your debug method. Unit tests work with OpenOCD and Segger J-Link, so we select OpenOCD here:\"\"<\/a><\/li>\n
  7. Press “Finish” to create your project. VisualGDB will create a basic project with 3 tests. Check the SuccessfulTest1<\/strong> test for a quick overview of various checks supported by the test framework:\"\"<\/a><\/li>\n
  8. Build your project and select Test->Run->All Tests<\/strong> to verify that the tests can be started properly. Alternatively you can select the tests you want to run in the Test Explorer, right-click there and select “Run”: \"\"<\/a><\/li>\n
  9. Now we will measure the time taken by the sinf()<\/strong> function in soft-FP and hard-FP modes. On many ARM Cortex devices (including most STM32F4 devices) this can be done by enabling the debug cycle counter, setting the CYCCNT register to 0 before running a function and then reading the CYCCNT register immediately after. The following function demonstrates this:\n
    void MeasureSinTime()\r\n{\r\n\u00a0\u00a0\u00a0 volatile double arg = 0.1;\r\n\u00a0\u00a0\u00a0 CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;\r\n\u00a0\u00a0\u00a0 DWT->CTRL |= DWT_CTRL_CYCCNTENA_Msk;\r\n\u00a0\u00a0\u00a0 DWT->CYCCNT = 0;\r\n\u00a0\u00a0\u00a0 volatile float result = sinf(arg);\r\n\u00a0\u00a0\u00a0 volatile unsigned cycles = DWT->CYCCNT;\r\n\u00a0\u00a0\u00a0 asm(\"nop\");\r\n}<\/pre>\n<\/li>\n
  10. VisualGDB test projects are normal executable projects with a main() function. Hence you can quickly prototype things by calling functions like this one directly from main() after the HAL_Init() call. Then set a breakpoint at the “nop” line and start debugging. Once the breakpoint is hit, note down the value of the “cycles” variable:\"\"<\/a>Note how the IsRunningUnitTests()<\/strong> check in main() <\/strong>is used to distinguish regular debug sessions from unit test runs. It will only return true when running or debugging unit tests via the VisualGDB interfaces.<\/li>\n
  11. Now we will switch the project to the software floating point mode:\"\"<\/a><\/li>\n
  12. Build it and check the new time:\"\"<\/a>Using the hardware FP mode makes more than 7.5x difference! So if a toolchain update or an accidental change in settings breaks this setting, the performance impact could be critical.<\/li>\n
  13. Now let’s make a simple test that will automatically verify that the sinf()<\/strong> function completes in time. Declaring tests using TinyEmbeddedTest and CppUTest consists of 2 steps:\n