STM32F303芯片，72M的主頻，GPIO的達(dá)到了14.4M的翻轉(zhuǎn)速率

再來(lái)上代碼：

RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOC, ENABLE);

GPIOC->MODER |= 0x55555555;

GPIOC->OSPEEDR |= 0xFFFFFFF;

GPIOC->PUPDR |= 0x55555555;

u32 Gpio_data[4]= {0x0000FFFF,0xFFFF0000,0x0000FFFF,0xFFFF0000};

DMA_InitTypeDef DMA_InitStructure;

TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;

NVIC_InitTypeDef NVIC_InitStructure;

/* TIMx clock enable */

RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM4, ENABLE);

/* DMAx clock enable */

RCC_AHBPeriphClockCmd(RCC_AHBPeriph_DMA1, ENABLE);

DMA_DeInit(DMA1_Channel7);

DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t)(&(GPIOC->BSRR));

DMA_InitStructure.DMA_MemoryBaseAddr = (uint32_t)Gpio_data;

DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralDST;

DMA_InitStructure.DMA_BufferSize = 4;

DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;

DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;

DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Word;

DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_Word;

DMA_InitStructure.DMA_Mode = DMA_Mode_Circular;

DMA_InitStructure.DMA_Priority = DMA_Priority_VeryHigh;

DMA_InitStructure.DMA_M2M = DMA_M2M_Enable;

DMA_Init(DMA1_Channel7, &DMA_InitStructure);

DMA1_Channel7->CCR |= DMA_CCR_EN;

　　用DMA內(nèi)存到內(nèi)存的模式，直接把Gpio_data的數(shù)據(jù)循環(huán)的搬到GPIOC的BSRR寄存器上來(lái)控制GPIOC上電平的翻轉(zhuǎn)，這樣使得GPIO的速度達(dá)到了最快，輸出70ns的脈寬，這已經(jīng)是達(dá)到了DMA總線帶寬的極限，要想再提高速度的話，就得提高STM32芯片的主頻。

　　再來(lái)看用代碼來(lái)實(shí)現(xiàn)的話，GPIO能達(dá)到多快的速度。

　　先是用庫(kù)函數(shù)來(lái)操作，在Main函數(shù)的While循環(huán)來(lái)翻轉(zhuǎn)電平

while(1)

{

GPIO_Write(GPIOC,0xffff);

GPIO_Write(GPIOC,0x0000);

}

可以看到最快只能輸出320ns的脈寬電平，而且高低電平脈寬還不一樣，那是因?yàn)樘幚韜hile(1)占用了CPU的時(shí)間導(dǎo)致的。

再來(lái)看用寄存器直接操作GPIO

while(1)

{

GPIOC->ODR = 0xFFFF;

GPIOC->ODR = 0x0000;

}

可以看到，最小脈寬電平可以達(dá)到40ns,直接操作寄存器的速度明顯要到庫(kù)函數(shù)操作要快好多，低電平的時(shí)間要比高電平的時(shí)間長(zhǎng)很多，同樣也是因?yàn)樘幚韜hile的原因。

用CPU操作寄存器可以達(dá)到最快的電平翻轉(zhuǎn)，但是這樣CPU的資源全用在這上面，不能再做其它的操作。如果用DMA的話，完全可以不占用CPU資源來(lái)達(dá)到更高速率的GPIO翻轉(zhuǎn)速度。假如我們要根據(jù)自己的需求來(lái)產(chǎn)生我們所需要的時(shí)序，那要怎樣做。其實(shí)也很簡(jiǎn)單，我們只要用定時(shí)器觸發(fā)DMA搬一次數(shù)據(jù)到BSRR寄存器，然后再通過(guò)調(diào)整Gpio_data數(shù)組里的數(shù)據(jù)，就可以來(lái)實(shí)現(xiàn)我們所要的時(shí)序。

下面的代碼就是通過(guò)這種方式來(lái)實(shí)現(xiàn)讓GPIOC產(chǎn)生1us脈寬的時(shí)鐘，

RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOC, ENABLE);

GPIOC->MODER |= 0x55555555;

GPIOC->OSPEEDR |= 0xFFFFFFF;

GPIOC->PUPDR |= 0x55555555;

u32 Gpio_data[4]= {0x0000FFFF,0xFFFF0000,0x0000FFFF,0xFFFF0000};

DMA_InitTypeDef DMA_InitStructure;

TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;

NVIC_InitTypeDef NVIC_InitStructure;

/* TIMx clock enable */

RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM4, ENABLE);

/* DMAx clock enable */

RCC_AHBPeriphClockCmd(RCC_AHBPeriph_DMA1, ENABLE);

DMA_DeInit(DMA1_Channel7);

DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t)(&(GPIOC->BSRR));

DMA_InitStructure.DMA_MemoryBaseAddr = (uint32_t)Gpio_data;

DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralDST;

DMA_InitStructure.DMA_BufferSize = 4;

DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;

DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;

DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Word;

DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_Word;

DMA_InitStructure.DMA_Mode = DMA_Mode_Circular;

DMA_InitStructure.DMA_Priority = DMA_Priority_VeryHigh;

DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;

DMA_Init(DMA1_Channel7, &DMA_InitStructure);

TIM_TimeBaseStructure.TIM_Period = 72;

TIM_TimeBaseStructure.TIM_Prescaler = 0x0;

TIM_TimeBaseStructure.TIM_ClockDivision = 0x0;

TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;

TIM_TimeBaseInit(TIM4, &TIM_TimeBaseStructure);

TIM_DMACmd(TIM4, TIM_DMA_Update, ENABLE);

TIM_SelectOutputTrigger(TIM4,TIM_TRGOSource_Update);

TIM_Cmd(TIM4, ENABLE);

DMA1_Channel7->CCR |= DMA_CCR_EN;