第一步：
在stm32f4xx.h中定义宏__FPU_PRESENT ; __FPU_USED #define __CM4_REV 0x0001 /*!< Core revision r0p1 */ #define __MPU_PRESENT 1 /*!< STM32F4XX provides an MPU */ #define __NVIC_PRIO_BITS 4 /*!< STM32F4XX uses 4 Bits for the Priority Levels */ #define __Vendor_SysTickConfig 0 /*!< Set to 1 if different SysTick Config is used */ #define __FPU_PRESENT 1 /*!< FPU present */ #define __FPU_USED 1 第二步：
在stm32f4xx.h中增加头文件arm_math.h #include "core_cm4.h" /* Cortex-M4 processor and core peripherals */ #include "system_stm32f4xx.h" #include #include "arm_math.h" 第三步：
在system_stm32f4xx.c的SystemInit()中添加如下代码： void SystemInit(void) { /* FPU settings ------------------------------------------------------------*/ #if (__FPU_PRESENT == 1) && (__FPU_USED == 1) SCB->CPACR |= ((3UL << 10*2)|(3UL << 11*2)); /* set CP10 and CP11 Full Access */ #endif 第四步：
在配置的c++界面添加宏定义ARM_MATH_CM4, __CC_ARM
第五步 ：
编译写个测试程序测试下代码 static void TaskProcess(void) { static uint8_t flag = 0; static uint8_t eeprom_cmd = 1; static uint16_t i = 0; static float num_f = 0; static float a = 3.1415926; static float b = 87.6; static float c = 76.987; sd_card_test(); TIM_SetCounter(RUNTIMER_TIM, 0); num_f = a * b / c; printf("t %dus ",TIM_GetCounter(RUNTIMER_TIM)); while(1); while (1) { printf("Hello STM32"); } } 定时器时钟为84M，不分频。
开启FPU运算时长为22×1/84 us;
不开启FPU运算时长为192×1/84 us；
可见开启FPU浮点运算乘除法快了8.7倍!!!