STM32开发笔记95: 处理UNUSED宏

单片机型号：STM32F091RCT6

使用C语音在PlatformIO中进行STM32Cube的工程设计，一切正常，希望使用C++语音进行程序开发，顾将main.c文件改为main.cpp文件，再次编译报如下警告：

In file included from C:\users\snmplink\.platformio\packages\framework-stm32cube\f0\Drivers\STM32F0xx_HAL_Driver\Inc/stm32f0xx_hal_rcc.h:45:0,
                 from C:\users\snmplink\.platformio\packages\framework-stm32cube\f0\Drivers\STM32F0xx_HAL_Driver\Inc/stm32f0xx_hal_conf.h:185,
                 from C:\users\snmplink\.platformio\packages\framework-stm32cube\f0\Drivers\STM32F0xx_HAL_Driver\Inc/stm32f0xx_hal.h:46,
                 from include/main.h:31,
                 from src\5_LogicLayer\main.cpp:22:
src\5_LogicLayer\main.cpp: In function 'void MX_GPIO_Init()':
C:\users\snmplink\.platformio\packages\framework-stm32cube\f0\Drivers\STM32F0xx_HAL_Driver\Inc/stm32f0xx_hal_rcc.h:664:48: warning: conversion to void will not access object of type 'volatile uint32_t {aka volatile long unsigned int}'
                                         UNUSED(tmpreg); \
C:\users\snmplink\.platformio\packages\framework-stm32cube\f0\Drivers\STM32F0xx_HAL_Driver\Inc/stm32f0xx_hal_def.h:87:27: note: in definition of macro 'UNUSED'
 #define UNUSED(x) ((void)(x))
                           ^
src\5_LogicLayer\main.cpp:166:3: note: in expansion of macro '__HAL_RCC_GPIOF_CLK_ENABLE'
   __HAL_RCC_GPIOF_CLK_ENABLE();
   ^~~~~~~~~~~~~~~~~~~~~~~~~~
C:\users\snmplink\.platformio\packages\framework-stm32cube\f0\Drivers\STM32F0xx_HAL_Driver\Inc/stm32f0xx_hal_rcc.h:650:48: warning: conversion to void will not access object of type 'volatile uint32_t {aka volatile long unsigned int}'
                                         UNUSED(tmpreg); \
C:\users\snmplink\.platformio\packages\framework-stm32cube\f0\Drivers\STM32F0xx_HAL_Driver\Inc/stm32f0xx_hal_def.h:87:27: note: in definition of macro 'UNUSED'
 #define UNUSED(x) ((void)(x))
                           ^
src\5_LogicLayer\main.cpp:167:3: note: in expansion of macro '__HAL_RCC_GPIOB_CLK_ENABLE'
   __HAL_RCC_GPIOB_CLK_ENABLE();
   ^~~~~~~~~~~~~~~~~~~~~~~~~~
C:\users\snmplink\.platformio\packages\framework-stm32cube\f0\Drivers\STM32F0xx_HAL_Driver\Inc/stm32f0xx_hal_rcc.h:643:48: warning: conversion to void will not access object of type 'volatile uint32_t {aka volatile long unsigned int}'
                                         UNUSED(tmpreg); \
C:\users\snmplink\.platformio\packages\framework-stm32cube\f0\Drivers\STM32F0xx_HAL_Driver\Inc/stm32f0xx_hal_def.h:87:27: note: in definition of macro 'UNUSED'
 #define UNUSED(x) ((void)(x))
                           ^
src\5_LogicLayer\main.cpp:168:3: note: in expansion of macro '__HAL_RCC_GPIOA_CLK_ENABLE'
   __HAL_RCC_GPIOA_CLK_ENABLE();

警告的内容较多，可以一级级分析，最后可将警告语句定位在下列文件：

C:\users\snmplink\.platformio\packages\framework-stm32cube\f0\Drivers\STM32F0xx_HAL_Driver\Inc/stm32f0xx_hal_rcc.h:664:48

代码如下：

#define __HAL_RCC_GPIOA_CLK_ENABLE()   do { \
                                        __IO uint32_t tmpreg; \
                                        SET_BIT(RCC->AHBENR, RCC_AHBENR_GPIOAEN);\
                                        /* Delay after an RCC peripheral clock enabling */\
                                        tmpreg = READ_BIT(RCC->AHBENR, RCC_AHBENR_GPIOAEN);\
                                        UNUSED(tmpreg); \
                                      } while(0U)
#define __HAL_RCC_GPIOB_CLK_ENABLE()   do { \
                                        __IO uint32_t tmpreg; \
                                        SET_BIT(RCC->AHBENR, RCC_AHBENR_GPIOBEN);\
                                        /* Delay after an RCC peripheral clock enabling */\
                                        tmpreg = READ_BIT(RCC->AHBENR, RCC_AHBENR_GPIOBEN);\
                                        UNUSED(tmpreg); \
                                      } while(0U)
#define __HAL_RCC_GPIOC_CLK_ENABLE()   do { \
                                        __IO uint32_t tmpreg; \
                                        SET_BIT(RCC->AHBENR, RCC_AHBENR_GPIOCEN);\
                                        /* Delay after an RCC peripheral clock enabling */\
                                        tmpreg = READ_BIT(RCC->AHBENR, RCC_AHBENR_GPIOCEN);\
                                        UNUSED(tmpreg); \
                                      } while(0U)
#define __HAL_RCC_GPIOF_CLK_ENABLE()   do { \
                                        __IO uint32_t tmpreg; \
                                        SET_BIT(RCC->AHBENR, RCC_AHBENR_GPIOFEN);\
                                        /* Delay after an RCC peripheral clock enabling */\
                                        tmpreg = READ_BIT(RCC->AHBENR, RCC_AHBENR_GPIOFEN);\
                                        UNUSED(tmpreg); \
                                      } while(0U)
#define __HAL_RCC_CRC_CLK_ENABLE()   do { \
                                        __IO uint32_t tmpreg; \
                                        SET_BIT(RCC->AHBENR, RCC_AHBENR_CRCEN);\
                                        /* Delay after an RCC peripheral clock enabling */\
                                        tmpreg = READ_BIT(RCC->AHBENR, RCC_AHBENR_CRCEN);\
                                        UNUSED(tmpreg); \
                                      } while(0U)
#define __HAL_RCC_DMA1_CLK_ENABLE()   do { \
                                        __IO uint32_t tmpreg; \
                                        SET_BIT(RCC->AHBENR, RCC_AHBENR_DMA1EN);\
                                        /* Delay after an RCC peripheral clock enabling */\
                                        tmpreg = READ_BIT(RCC->AHBENR, RCC_AHBENR_DMA1EN);\
                                        UNUSED(tmpreg); \
                                      } while(0U)
#define __HAL_RCC_SRAM_CLK_ENABLE()   do { \
                                        __IO uint32_t tmpreg; \
                                        SET_BIT(RCC->AHBENR, RCC_AHBENR_SRAMEN);\
                                        /* Delay after an RCC peripheral clock enabling */\
                                        tmpreg = READ_BIT(RCC->AHBENR, RCC_AHBENR_SRAMEN);\
                                        UNUSED(tmpreg); \
                                      } while(0U)
#define __HAL_RCC_FLITF_CLK_ENABLE()   do { \
                                        __IO uint32_t tmpreg; \
                                        SET_BIT(RCC->AHBENR, RCC_AHBENR_FLITFEN);\
                                        /* Delay after an RCC peripheral clock enabling */\
                                        tmpreg = READ_BIT(RCC->AHBENR, RCC_AHBENR_FLITFEN);\
                                        UNUSED(tmpreg); \
                                      } while(0U)

具体语句为：

UNUSED(tmpreg)

仔细分析以上语句可以看出程序中定义了tmpreg变量，并给tmpreg进行了赋值操作，但是并没有使用tmpreg变量。如果不使用UNUSED(tmpreg)语句，则会报“变量已赋值，但没有使用”的警告。所以UNUSED(tmpreg)是为了避免警告发生。

再看UNUSED宏的实现代码，在下列文件中：

C:\users\snmplink\.platformio\packages\framework-stm32cube\f0\Drivers\STM32F0xx_HAL_Driver\Inc/stm32f0xx_hal_def.h:87:27:

具体程序如下：

#define UNUSED(x) ((void)(x))

可看到GCC认为不应将volatile uint32_t变量强制转换为void类型。

由于这条警告没有提示类型，我在网上查找很长时间，均没有找到屏蔽的方法，故考虑直接解决，实际上避免“变量已赋值，但没有使用”的警告，还有另外一种方法，就是使用如下宏：

#define UNUSED(x) ((x) = (x))

将UNUSED宏修改后，问题解决。

snmplink

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STM32开发笔记95: 处理UNUSED宏

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