我正在STM32 F411 Blackpill板上为W25 Q（25 Q64 FVSIG）编写CMSIS顶部的SPI驱动程序。我的问题是闪存不响应通过SPI的信号。MCU配置为主，闪存配置为从。产生时钟和MOSI信号，CS设置为低电平。然而，我没有观察到MISO的答案，如下图所示。
引脚Map：（PA4 - CS）（PA5 - SCK）（PA7 - MOSI）（PB4 - MISO）
我怀疑闪存芯片有问题，但换成新的后，我观察到没有改善。与此同时，我看着代码和波形，却不知道我做错了什么。我身边也没有人陪我看。所以我指望你的帮助！
Oscilloscope measurement picture - attempt to read JEDEC ID
这是我的驱动程序代码的样子：

uint32_t w25_pin_spi_init(void)
{
    RCC->AHB1ENR |= RCC_AHB1ENR_GPIOAEN;
    RCC->AHB1ENR |= RCC_AHB1ENR_GPIOBEN;
    /* setup alternate functions of PA5/PA7/PB4 and output to PA4 (NSS)*/
    GPIOA->MODER &= ~GPIO_MODER_MODE4;
    GPIOA->MODER &= ~GPIO_MODER_MODE5;
    GPIOA->MODER &= ~GPIO_MODER_MODE7;
    GPIOB->MODER &= ~GPIO_MODER_MODE4;

    GPIOA->MODER |= GPIO_MODER_MODE4_0; //output
    GPIOA->MODER |= GPIO_MODER_MODE5_1; //alternate
    GPIOA->MODER |= GPIO_MODER_MODE7_1;
    GPIOB->MODER |= GPIO_MODER_MODE4_1;

    GPIOA->OSPEEDR |= (GPIO_OSPEEDR_OSPEED4_0 | GPIO_OSPEEDR_OSPEED4_1);

    /* OTYPER in reset state */
    GPIOA->PUPDR &= ~GPIO_PUPDR_PUPD5;
    GPIOA->PUPDR &= ~GPIO_PUPDR_PUPD7;
    GPIOB->PUPDR &= ~GPIO_PUPDR_PUPD4;
    GPIOA->PUPDR &= ~GPIO_PUPDR_PUPD4;
    /* pull-up for MISO */
    GPIOB->PUPDR |= GPIO_PUPDR_PUPD4_0;

    GPIOA->AFR[0] |= (GPIO_AFRL_AFSEL5_0 | GPIO_AFRL_AFSEL5_2);
    GPIOA->AFR[0] |= (GPIO_AFRL_AFSEL7_0 | GPIO_AFRL_AFSEL7_2);
    GPIOB->AFR[0] |= (GPIO_AFRL_AFSEL4_0 | GPIO_AFRL_AFSEL4_2);

    return 0;
}

void w25_CS_enable(void)
{
    GPIOA->BSRR |= GPIO_BSRR_BR4;
}

void w25_CS_disable (void)
{
    GPIOA->BSRR |= GPIO_BSRR_BS4;
}

uint32_t w25_spi_init(void)
{
    RCC->APB2ENR |= RCC_APB2ENR_SPI1EN;
    SPI1->CR1 &= ~SPI_CR1_DFF;
    SPI1->CR1 |= (SPI_CR1_BR_2 | SPI_CR1_BR_1 | SPI_CR1_BR_0);
    SPI1->CR1 |= SPI_CR1_MSTR;
    SPI1->CR1 |= SPI_CR1_SSM;
    SPI1->CR1 |= SPI_CR1_SSI;
    SPI1->CR1 |= SPI_CR1_SPE;
    return 0;
}

uint16_t w25_send_receive_data(uint16_t data)
{
    while(!(SPI1->SR & SPI_SR_TXE));
    SPI1->DR = data;
    while(!(SPI1->SR & SPI_SR_RXNE));
    return SPI1->DR;
}

它的使用方式是读取JEDEC ID：

w25_pin_spi_init();
w25_spi_init();
[...]
w25_CS_enable();
w25_send_receive_data(0x9F);
uint16_t manuf = w25_send_receive_data(0x00);
uint16_t mem_type = w25_send_receive_data(0x00);
uint16_t capa = w25_send_receive_data(0x00);
w25_CS_disable();

/WP和/FLASH引脚通过电路板设计设置为高电平，原理图如下所示。
STM32 F411 Blackpill原理图（左下角 Flink ）：STM32F411 Blackpill schematic