为什么从STM32F407G-Disc1单片机上的lis3dsh加速度计读取数据时只得到0xff?

所以我正在学习嵌入式开发,最近我学习了SPI的基础知识。作为一个项目,我想与我的STM32F407G-DISC1板上的lis3dsh加速度计通信,只使用CMSIS头。

我把整个代码粘贴到下面,但我会先解释它,因为没人想读所有的代码。

作为参考,这些是通过SPI进行通信所需的管脚(根据MCU的数据表):

• PA5-SPI1_SCK
• PA7-Spi1 ou Mosi公司
• PA6-SPI1-米索
• PE3-碳钢I2c/SPI

以下是我在代码中采取的步骤:

1. 使用AHB1ENR寄存器为GPIOA和GPIOE启用时钟。
2. 对于GPIOA,我将三个管脚设置为备用功能,输出为推拉,速度低,无上拉/下拉,并将备用功能配置为SPI。
3. 对于gpioe,将其设置为gpio模式、推拉、低速、上拉,然后将其设置为高(如写入BSSR寄存器中所示)。
4. 使用APB2ENR寄存器为SPI启用时钟。
5. 配置SPI1:首先禁用它,启用2线单向模式,将波特率设置为fpcl/16,因为APB2外围时钟为84MHz,加速度计的最大时钟为10MHz。然后将时钟相位和极性设置为1。8位数据帧,最高位优先,启用软件从管理,也启用主配置。最后,启用SPI1。
6. 在所有这些之后,我将0x63发送到加速度计的0x20寄存器。这将输出速率设置为100Hz,并启用X轴和Y轴。我不知道这是否真的有效。我假设这是因为检查SPI状态寄存器时,TX缓冲区是空的。
7. 然后,为了测试我是否可以接收,我尝试从加速度计的“谁是谁”寄存器中获取数据。但我只在调试垃圾数据时看到它(0xFF)。

我在谷歌上搜索了一下为什么会出现这种情况,很多人认为时钟的极性和相位可能不正确。但是,我已经检查了多次,我很确定我已经正确地配置了它。

我试过设置中断。在中断期间,即使RXNE(RX缓冲区不是空的)为真,它仍然只读取0xFF。我不明白为什么会发生这种事。

代码如下。起点是 accelerometer_init() .从我注册的人处读取数据 turn_on_accelerometer() .

#include <stdint.h>
#include <stdbool.h>
#include "stm32f4xx.h"
#include "accelerometer.h"

static void gpio_clock_enable(void);
static void gpio_a_init(void);
static void gpio_e_init(void);
static void accelerometer_clock_enable(void);
static void configure_accelerometer(void);
static void pull_slave_high(void);
static void pull_slave_low(void);
static void turn_on_accelerometer(void);
static void wait_till_transmit_complete(void);
static void transmit_only(uint8_t address, uint8_t data);
static void receive_dummy_data(void);

void accelerometer_init(void) {
    gpio_clock_enable();
    gpio_a_init();
    gpio_e_init();

    accelerometer_clock_enable();
    configure_accelerometer();
    turn_on_accelerometer();
}

void gpio_clock_enable(void) {
    RCC_TypeDef *rcc = RCC;
    rcc->AHB1ENR |= (1 << 0) | (1 << 4);
}

void gpio_a_init(void) {
    GPIO_TypeDef *gpio_a = GPIOA;

    // Reset mode and set as alternate function
    gpio_a->MODER &= ~(0x3 << 10) & ~(0x3 << 12) & ~(0x3 << 14);
    gpio_a->MODER |= (0x2 << 10) | (0x2 << 12) | (0x2 << 14);

    // Set output to PP
    gpio_a->OTYPER &= ~(1 << 5) & ~(1 << 6) & ~(1 << 7);

    // Set speed to low
    gpio_a->OSPEEDR &= ~(0x3 << 10) & ~(0x3 << 12) & ~(0x3 << 14);

    // Set to no pull-up / pull-down
    gpio_a->PUPDR &= ~(0x3 << 10) & ~(0x3 << 12) & ~(0x3 << 14);

    // Reset alternate function and set to SPI
    gpio_a->AFR[0] &= ~(0xF << 20) & ~(0xF << 24) & ~(0xF << 28);
    gpio_a->AFR[0] |= (0x5 << 20) | (0x5 << 24) | (0x5 << 28);
}

void gpio_e_init(void) {
    GPIO_TypeDef *gpio_e = GPIOE;

    // Set as general purpose output mode
    gpio_e->MODER &= ~(0x3 << 6);
    gpio_e->MODER |= (1 << 6);

    // Set as push pull
    gpio_e->OTYPER &= ~(1 << 3);

    // Set as low speed
    gpio_e->OSPEEDR &= ~(0x3 << 6);

    // Set to pull up
    gpio_e->PUPDR &= ~(0x3 << 6);
    gpio_e->PUPDR |= (1 << 6);

    // Set it high
    pull_slave_high();
}

void accelerometer_clock_enable(void) {
    RCC_TypeDef *rcc = RCC;
    rcc->APB2ENR |= (1 << 12);
}

void configure_accelerometer(void) {
    SPI_TypeDef *spi_1 = SPI1;

    // First disable it while we configure SPI
    spi_1->CR1 &= ~(1 << 6);

    // 2-line unidirectional data mode enabled
    spi_1->CR1 &= ~(1 << 15);

    // Reset baud rate and set to fPCLK/16
    // because APB2 peripheral clock currently is 84 MHz
    // and the max clock of the accelerometer is 10 MHz.
    spi_1->CR1 &= ~(0x7 << 3);
    spi_1->CR1 |= (0x3 << 3);

    // Set clock phase to 1
    spi_1->CR1 |= (1 << 0);

    // Set clock polarity to 1
    spi_1->CR1 |= (1 << 1);

    // 8 bit data frame format
    spi_1->CR1 &= ~(1 << 11);

    // MSB first
    spi_1->CR1 &= ~(1 << 7);

    // Software slave management enabled
    spi_1->CR1 |= (1 << 9);
    spi_1->CR1 |= (1 << 8);

    // Master configuration enabled
    spi_1->CR1 |= (1 << 2);

    // SS output enabled
//    spi_1->CR2 |= (1 << 2);

    // Enable SPI
    spi_1->CR1 |= (1 << 6);

    // Wait a little bit for accelerometer to turn on
    for (int i=0; i<1000000; i++);
}

void pull_slave_high(void) {
    // Wait until SPI is no longer busy
    SPI_TypeDef *spi_1 = SPI1;
    while ((spi_1->SR >> 7) & 1);

    GPIO_TypeDef *gpio_e = GPIOE;
    gpio_e->BSRR |= (1 << 19);
}

void pull_slave_low(void) {
    // Wait until SPI is no longer busy
    SPI_TypeDef *spi_1 = SPI1;
    while ((spi_1->SR >> 7) & 1);

    GPIO_TypeDef *gpio_e = GPIOE;
    gpio_e->BSRR |= (1 << 3);
}

void turn_on_accelerometer(void) {
    // Set output data rate to 100Hz
    // and enable X-axis, Y-axis.
    transmit_only(0x20, 0x63);
    receive_dummy_data();

    // Temp test checking the WHO_AM_I register on the accelerometer.
    SPI_TypeDef *spi_1 = SPI1;
    pull_slave_low();
    wait_till_transmit_complete();
    uint8_t address = 0x0F | 0x80;
    spi_1->DR = address;
    wait_till_transmit_complete();

    while (true) {
        volatile bool is_busy = (spi_1->SR >> 7) & 1;
        volatile bool is_rx_buffer_not_empty = (spi_1->SR >> 0) & 1;

        if (!is_busy && is_rx_buffer_not_empty) {
            break;
        }
    }
    volatile uint32_t data = spi_1->DR;
    pull_slave_high();
}

/*
 * Transmit is synchronous.
 */
void transmit_only(uint8_t address, uint8_t data) {
    SPI_TypeDef *spi_1 = SPI1;

    // Select the accelerometer as the slave
    pull_slave_low();

    // Wait till transmit buffer is ready
    wait_till_transmit_complete();

    spi_1->DR = address;

    // Wait till transmit buffer is ready
    wait_till_transmit_complete();

    spi_1->DR = data;

    // Wait till transmit buffer has been read
    wait_till_transmit_complete();

    // Deselect the slave
    pull_slave_high();
}

void wait_till_transmit_complete(void) {
    SPI_TypeDef *spi_1 = SPI1;

    while (true) {
        volatile bool is_busy = (spi_1->SR >> 7) & 1;
        volatile bool is_transmit_buffer_empty = (spi_1->SR >> 1) & 1;

        if (!is_busy && is_transmit_buffer_empty) {
            break;
        }
    }
}

void receive_dummy_data(void) {
    SPI_TypeDef *spi_1 = SPI1;
    spi_1->DR;
    spi_1->SR;
}