RCC_DeInit();
- RCC_HSEConfig(RCC_HSE_ON);
- Errsts = RCC_WaitForHSEStartUp();
- if (Errsts == SUCCESS)
- {
- FLASH_PrefetchBufferCmd(FLASH_PrefetchBuffer_Enable);
- RCC_PLLConfig(RCC_PLLSource_HSE_Div2, RCC_PLLMul_9);
- RCC_PLLCmd(ENABLE);
- while (RCC_GetFlagStatus(RCC_FLAG_PLLRDY == RESET))
- {
- }
- FLASH_SetLatency(FLASH_Latency_1);
- RCC_SYSCLKConfig(RCC_SYSCLKSource_PLLCLK);
- RCC_HCLKConfig(RCC_SYSCLK_Div1);
- RCC_PCLK1Config(RCC_HCLK_Div2);
- RCC_PCLK2Config(RCC_HCLK_Div1);
- while (RCC_GetSYSCLKSource() != 0x08)
- {
- }
- }
上面是rcc的初始设置,我用的hse作为芯片的时钟信号,根据上面的code可以算出apb2(pclk2)的时钟信号是36mhz,所以我的spi也应该是36mhz。
下面是我的spi初始化设置:
{
- SPI_InitTypeDef SPI_InitStructure;
- GPIO_InitTypeDef GPIO_InitStructure;
- RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOB, ENABLE);
- RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);
- RCC_APB2PeriphClockCmd(RCC_APB2Periph_SPI1, ENABLE);
- GPIO_InitStructure.GPIO_Pin = GPIO_Pin_5| GPIO_Pin_6| GPIO_Pin_7;
- GPIO_InitStructure.GPIO_Speed = GPIO_Speed_10MHz;
- GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
- GPIO_Init(GPIOA, GPIO_InitStructure);
- GPIO_InitStructure.GPIO_Pin = GPIO_Pin_4;
- GPIO_InitStructure.GPIO_Speed = GPIO_Speed_10MHz;
- GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
- GPIO_Init(GPIOA, GPIO_InitStructure);
- GPIO_WriteBit(GPIOA, GPIO_Pin_4,Bit_SET);
- SPI_InitStructure.SPI_Direction = SPI_Direction_2Lines_FullDuplex;
- SPI_InitStructure.SPI_Mode = SPI_Mode_Master;
- SPI_InitStructure.SPI_DataSize = SPI_DataSize_8b;
- SPI_InitStructure.SPI_CPOL = SPI_CPOL_Low;
- SPI_InitStructure.SPI_CPHA = SPI_CPHA_1Edge;
- SPI_InitStructure.SPI_NSS = SPI_NSS_Soft;
- SPI_InitStructure.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_4;
- SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB;
- SPI_InitStructure.SPI_CRCPolynomial = 7;
- SPI_Init(SPI1, SPI_InitStructure);
- /* Enable SPI2 */
- SPI_Cmd(SPI1, ENABLE);
- }
这里SPI_BaudRatePrescaler_4将spi 时钟信号分频了4,理论上spi现在应该是36mhz/4=9mhz。但是我用示波器观测sck管脚,只有200khz左右,而且我不断改变SPI_BaudRatePrescaler的值,发现结果也不是线性的,很奇怪。所以想问一下这个到底是什么原因。
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