I don't understand this marco in stm32 HAL library: #define assert_param(expr) ((void)0U)

Question

I'm a newbie just starting to learn about stm32 and have some confusion with the HAL library, thank you so much for taking the time to help.

I used STM32 to generate code, in the MX_GPIO_Init() and then try to understand how these functions work but i don't fully understand. -Marco below initializes portC's clk, but why put it in a loop that is sure to run only once:

#define __HAL_RCC_GPIOC_CLK_ENABLE()   do { \
                                        __IO uint32_t tmpreg; \
                                        SET_BIT(RCC->APB2ENR, RCC_APB2ENR_IOPCEN);\
                                        /* Delay after an RCC peripheral clock enabling */\
                                        tmpreg = READ_BIT(RCC->APB2ENR, RCC_APB2ENR_IOPCEN);\
                                        UNUSED(tmpreg); \
                                      } while(0U)

-i want to ask an other question, i understand this code is checking if the GPIOx is valid

assert_param(IS_GPIO_ALL_INSTANCE(GPIOx));

but:

#define assert_param(expr) ((void)0U);

As I understand, assert_param(IS_GPIO_ALL_INSTANCE(GPIOx)); will be replaced by ((void)0U), where did I misunderstand?

i know it is important to understand and able to build project from scratch. But in companies, will project use libraries like HAL?

That is two separate questions, and the first does not relate to your title. You should post the questions separately. — Clifford, May 11 '23 at 21:32

pmacfarlane · Accepted Answer · 2023-05-11T12:11:15.783

The do { } while(0) construct is to allow you to invoke the macro and put a ; at the end of it. i.e. you want to be able to have:

__HAL_RCC_GPIOC_CLK_ENABLE();

There is a lot more information about that here: do { ... } while (0) — what is it good for?

As to your question about:

#define assert_param(expr) ((void)0U);

This is a disabled assert, because you have not defined USE_FULL_ASSERT. It basically does nothing. If you define USE_FULL_ASSERT in your project, assert_param() will be defined as an actual assert. From a random project I have open:

#ifdef  USE_FULL_ASSERT
/**
  * @brief  The assert_param macro is used for functions parameters check.
  * @param  expr If expr is false, it calls assert_failed function
  *         which reports the name of the source file and the source
  *         line number of the call that failed.
  *         If expr is true, it returns no value.
  * @retval None
  */
#define assert_param(expr) ((expr) ? (void)0U : assert_failed((uint8_t *)__FILE__, __LINE__))
/* Exported functions ------------------------------------------------------- */
void assert_failed(uint8_t *file, uint32_t line);
#else
#define assert_param(expr) ((void)0U)
#endif /* USE_FULL_ASSERT */

To enable USE_FULL_ASSERT, open your .ioc file in CubeIDE, click on the Project Manager tab at the top, click the Code Generator box on the left-hand side, and enable the Enable Full Assert tick-box.

the `do {} while (0)` construct doesn't just __allow you__ to add a semicolon at the end, it __forces you__ so it looks like a normal C/C++ line of code, and also doesn't give you a warning for a dead line of code if you have two `;` in a row. — Russ Schultz, May 11 '23 at 15:03

I don't understand this marco in stm32 HAL library: #define assert_param(expr) ((void)0U)

1 Answers1