关于工作频率修改的问题，用于USB上

bluezap · 发表于 2014-6-12 15:46:01

我现在遇到个问题，因为设备要省电所以，工作频率是8M,但是要接USB，所以接USB的时候频率要转成72M，现在我如果转成72MHZ后，我发现USB无法工作了，这个是什么原因

static void USB_Open(void)
{
EXTI_InitTypeDef EXTI_InitStructure;
NVIC_InitTypeDef NVIC_InitStructure;

MySetClock72M();
/* Select USBCLK source */
RCC_USBCLKConfig(RCC_USBCLKSource_PLLCLK_1Div5);

/* Enable the USB clock */
RCC_APB1PeriphClockCmd(RCC_APB1Periph_USB, ENABLE);

/* Configure the EXTI line 18 connected internally to the USB IP */
EXTI_ClearITPendingBit(EXTI_Line18);
EXTI_InitStructure.EXTI_Mode = EXTI_Mode_Interrupt;
EXTI_InitStructure.EXTI_Line = EXTI_Line18;
EXTI_InitStructure.EXTI_Trigger = EXTI_Trigger_Rising;
EXTI_InitStructure.EXTI_LineCmd = ENABLE;
EXTI_Init(&EXTI_InitStructure);

/* 2 bit for pre-emption priority, 2 bits for subpriority */
NVIC_PriorityGroupConfig(NVIC_PriorityGroup_2);

/* Enable the USB interrupt */
NVIC_InitStructure.NVIC_IRQChannel = USB_LP_CAN1_RX0_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 2;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);

/* Enable the USB Wake-up interrupt */
NVIC_InitStructure.NVIC_IRQChannel = USBWakeUp_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
NVIC_Init(&NVIC_InitStructure);

/* Call usb initialization */
USB_Init();
}

void MySetClock72M()
{
__IO uint32_t StartUpCounter = 0, HSEStatus = 0;

/* Reset the RCC clock configuration to the default reset state(for debug purpose) */
/* Set HSION bit */
RCC->CR |= (uint32_t)0x00000001;

/* Reset SW, HPRE, PPRE1, PPRE2, ADCPRE and MCO bits */

RCC->CFGR &= (uint32_t)0xF8FF0000;

/* Reset HSEON, CSSON and PLLON bits */
RCC->CR &= (uint32_t)0xFEF6FFFF;

/* Reset HSEBYP bit */
RCC->CR &= (uint32_t)0xFFFBFFFF;

/* Reset PLLSRC, PLLXTPRE, PLLMUL and USBPRE/OTGFSPRE bits */
RCC->CFGR &= (uint32_t)0xFF80FFFF;

#if defined (STM32F10X_LD_VL) || defined (STM32F10X_MD_VL) || (defined STM32F10X_HD_VL)
/* Disable all interrupts and clear pending bits */
RCC->CIR = 0x009F0000;

/* Reset CFGR2 register */
RCC->CFGR2 = 0x00000000;
#else
/* Disable all interrupts and clear pending bits */
RCC->CIR = 0x009F0000;
#endif /* STM32F10X_XX */

#if defined (STM32F10X_HD) || (defined STM32F10X_XL) || (defined STM32F10X_HD_VL)
#ifdef DATA_IN_ExtSRAM
    SystemInit_ExtMemCtl();
#endif /* DATA_IN_ExtSRAM */
#endif

/* SYSCLK, HCLK, PCLK2 and PCLK1 configuration ---------------------------*/
/* Enable HSE */
RCC->CR |= ((uint32_t)RCC_CR_HSEON);

/* Wait till HSE is ready and if Time out is reached exit */
do
{
    HSEStatus = RCC->CR & RCC_CR_HSERDY;
    StartUpCounter++;
} while((HSEStatus == 0) && (StartUpCounter != HSE_STARTUP_TIMEOUT));

if ((RCC->CR & RCC_CR_HSERDY) != RESET)
{
HSEStatus = (uint32_t)0x01;
}
else
{
HSEStatus = (uint32_t)0x00;
}

if (HSEStatus == (uint32_t)0x01)
{
/* Enable Prefetch Buffer */
FLASH->ACR |= FLASH_ACR_PRFTBE;

    /* Flash 2 wait state */
    FLASH->ACR &= (uint32_t)((uint32_t)~FLASH_ACR_LATENCY);
    FLASH->ACR |= (uint32_t)FLASH_ACR_LATENCY_2;

    /* HCLK = SYSCLK */
    RCC->CFGR |= (uint32_t)RCC_CFGR_HPRE_DIV1;

    /* PCLK2 = HCLK */
    RCC->CFGR |= (uint32_t)RCC_CFGR_PPRE2_DIV1;

    /* PCLK1 = HCLK */
    RCC->CFGR |= (uint32_t)RCC_CFGR_PPRE1_DIV2;

    /* PLL configuration: PLLCLK = HSE * 9 = 72 MHz */
    RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_PLLSRC | RCC_CFGR_PLLXTPRE |
                                        RCC_CFGR_PLLMULL));
    RCC->CFGR |= (uint32_t)(RCC_CFGR_PLLSRC_HSE | RCC_CFGR_PLLMULL9);

/* Enable PLL */
RCC->CR |= RCC_CR_PLLON;

    /* Wait till PLL is ready */
    while((RCC->CR & RCC_CR_PLLRDY) == 0)
    {
    }

    /* Select PLL as system clock source */
    RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_SW));
    RCC->CFGR |= (uint32_t)RCC_CFGR_SW_PLL;

    /* Wait till PLL is used as system clock source */
    while ((RCC->CFGR & (uint32_t)RCC_CFGR_SWS) != (uint32_t)0x08)
    {
    }
}
else
{ /* If HSE fails to start-up, the application will have wrong clock
         configuration. User can add here some code to deal with this error */
}

#ifdef VECT_TAB_SRAM
SCB->VTOR = SRAM_BASE | VECT_TAB_OFFSET; /* Vector Table Relocation in Internal SRAM. */
#else
SCB->VTOR = FLASH_BASE | VECT_TAB_OFFSET; /* Vector Table Relocation in Internal FLASH. */
#endif
}