写入 I2C 的缓冲区在读取时不返回

Question

我试图在写入后从 I2C 总线上的内存位置读取一个值。当我在终端中运行时，我得到了奇怪的输出。

这是我的程序

    #include <stdio.h>
    #include <stdlib.h>
    #include <stdint.h>
    #include <inttypes.h>

    #include <errno.h>
    #include <string.h>

    #include <sys/stat.h>
    #include <fcntl.h>
    #include <unistd.h>

    #include <linux/i2c.h>
    #include <linux/i2c-dev.h>
    #include <sys/ioctl.h>

    #define I2C_ADAPTER "/dev/i2c-0"
    #define I2C_DEVICE  0x00


    int main (int argc, char *argv[])
    {
        int file;
        int addr = 0X00; /* XGPIOPS_DATA_LOW_OFFSET */

        if((file = open(I2C_ADAPTER, O_RDWR)) < 0) {
            printf("Failed to open the bus");
            return -1;
        }

        if(ioctl(file, I2C_SLAVE, addr) < 0) {
            printf("Unable to open device as slave %s", strerror(errno));
            return -1;
        }

        char buf[10];

        buf[0] = addr;
        buf[1] = 0x10;
        if(write(file, buf, 2) != 2) {
            printf("Failed to write to bus %s.\n\n", strerror(errno));
        }
        else {
            printf("Successful write\n");
            printf(buf);
            printf("\n\n");
        }

        if(read(file, buf, 2) != 2) {
            printf("Failed to read from the i2c bus. %s\n\n", strerror(errno));
        }
        else {
            printf("Successful read\n");
            printf(buf);
            printf("\n\n");
        }

        return 0;
    }

The output from the program looks like this

Successful write

Successful read ��

在我的终端上，这些块看起来更像是钻石内部的问号。我不确定在 ASCII 中对应的是什么。

为什么我不读回我最初写入的地址字节后的第二个字节 0x10？

根据第一组答案，更新后的代码如下：

#include <stdio.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <inttypes.h>

#include <errno.h>
#include <string.h>

#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

#include <linux/i2c.h>
#include <linux/i2c-dev.h>
#include <sys/ioctl.h>

#define I2C_ADAPTER "/dev/i2c-0"
#define I2C_DEVICE  0x00


int main (int argc, char *argv[])
{
    int file;

    long addr, reg_addr;

    char *end;

    if(argc == 3) {
        addr = strtol(argv[1], &end, 16);
        printf("Value of addr is: %ld\n", addr);

        reg_addr = strtol(argv[2], &end, 16);
        printf("Value of reg_addr is: %ld\n", reg_addr);
    }
    else {
        printf("arg failed\n\n.");
        addr = 0x00;
    }


    if((file = open(I2C_ADAPTER, O_RDWR)) < 0) {
        printf("Failed to open the bus\n");
        return -1;
    }

    if(ioctl(file, I2C_SLAVE, addr) < 0) {
        printf("Unable to open device as slave \n%s\n", strerror(errno));
        return -1;
    }

    char buf[10];

    buf[0] = addr;
    buf[1] = reg_addr;
    buf[2] = 0x10;
    if(write(file, buf, 3) != 3) {
        printf("Failed to write to bus %s.\n\n", strerror(errno));
    }
    else {
        printf("Successful write\n");
        printf(buf);
        printf("\n\n");
    }

    if(read(file, buf, 3) != 3) {
        printf("Failed to read from the i2c bus.\n %s\n\n", strerror(errno));
    }
    else {
        printf("Successful read\n");
        printf("Buf = [%02X,%02X,%02X]\n", buf[0], buf[1], buf[2]);
        printf("\n\n");
    }

    return 0;
}

此时，每当我使用 0x00 作为地址时，无论 argv[2] 是什么，我都会得到 FF、FF、FF 作为输出。这是设备树文件的适用部分。请注意，这是被模拟的，所以我无法探测物理设备。

&i2c0 {
    status = "okay";
    clock-frequency = <400000>;
    pinctrl-names = "default";

    i2cswitch@74 {
        compatible = "nxp,pca9548";
        #address-cells = <1>;
        #size-cells = <0>;
        reg = <0x74>;

        i2c@0 {
            #address-cells = <1>;
            #size-cells = <0>;
            reg = <0>;
            si570: clock-generator@5d {
                #clock-cells = <0>;
                compatible = "silabs,si570";
                temperature-stability = <50>;
                reg = <0x5d>;
                factory-fout = <156250000>;
                clock-frequency = <148500000>;
            };
        };

        i2c@2 {
            #address-cells = <1>;
            #size-cells = <0>;
            reg = <2>;
            eeprom@54 {
                compatible = "at,24c08";
                reg = <0x54>;
            };
        };

        i2c@3 {
            #address-cells = <1>;
            #size-cells = <0>;
            reg = <3>;
            gpio@21 {
                compatible = "ti,tca6416";
                reg = <0x21>;
                gpio-controller;
                #gpio-cells = <2>;
            };
        };

        i2c@4 {
            #address-cells = <1>;
            #size-cells = <0>;
            reg = <4>;
            rtc@51 {
                compatible = "nxp,pcf8563";
                reg = <0x51>;
            };
        };

        i2c@7 {
            #address-cells = <1>;
            #size-cells = <0>;
            reg = <7>;
            hwmon@52 {
                compatible = "ti,ucd9248";
                reg = <52>;
            };
            hwmon@53 {
                compatible = "ti,ucd9248";
                reg = <53>;
            };
            hwmon@54 {
                compatible = "ti,ucd9248";
                reg = <54>;
            };
        };
    };
};

这里有几个示例测试

尝试测试 SiLabs 时钟发生器

root@plnx_arm:~# /usr/bin/i2c-test-mem-location 0x54 0x00

Value of addr is: 84

Value of reg_addr is: 0

Unable to open device as slave

Device or resource busy

尝试测试eeprom设备

root@plnx_arm:~# /usr/bin/i2c-test-mem-location 0x5d 0x00

Value of addr is: 93

Value of reg_addr is: 0

Unable to open device as slave

Device or resource busy

这是我第三次尝试的程序。考虑到答案中的注释后，我写了这个

#include <stdio.h>

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <inttypes.h>

#include <errno.h>
#include <string.h>

#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

#include <linux/i2c.h>
#include <linux/i2c-dev.h>
#include <sys/ioctl.h>

#define I2C_ADAPTER "/dev/i2c-0"
#define DEVICE_ADDRESS 0x54


int main (int argc, char *argv[])
{
    int file;

    uint8_t reg, value;

    char *end;

    printf("The device address on the bus: %d", DEVICE_ADDRESS);

    if(argc == 3) {
        reg = strtol(argv[1], &end, 16);

        printf("Value of register address: %d\n", reg);

        value = strtol(argv[2], &end, 16);
        printf("value to write is: %d\n", value);
    }
    else {
        printf("arg failed\n\n.");
    }


    if((file = open(I2C_ADAPTER, O_RDWR)) < 0) {
        printf("Failed to open the bus\n");
        return -1;
    }

    if(ioctl(file, I2C_SLAVE, DEVICE_ADDRESS) < 0) {
        printf("Unable to open device as slave \n%s\n", strerror(errno));
        return -1;
    }

    char buf[10];

    buf[0] = reg;
    buf[1] = value;

    if(write(file, buf, 2) != 2) {
        printf("Failed to write to bus %s.\n\n", strerror(errno));
    }
    else {
        printf("Successful write\n");
        printf(buf);
        printf("\n\n");
    }

    if(read(file, buf, 2) != 2) {
        printf("Failed to read from the i2c bus.\n %s\n\n", strerror(errno));
    }
    else {
        printf("Successful read\n");
        printf("Buf = [%02X,%02X,%02X]\n", buf[0], buf[1], buf[2]);
        printf("\n\n");
    }

    return 0;
}

不幸的是，我仍然遇到同样的错误。

root@plnx_arm:~# /usr/bin/i2c-test-mem-location 0x00 0x10

The device address on the bus: 84Value of register address: 0

value to write is: 16

Unable to open device as slave

Device or resource busy

root@plnx_arm:~# /usr/bin/i2c-test-mem-location 0x30 0x10

The device address on the bus: 84Value of register address: 48

value to write is: 16

Unable to open device as slave

Device or resource busy

Answer 1

编辑 2：我认为您可能没有正确设置 I2C 设备地址。你的 I2C_ADAPTER ("/dev/i2c-0") 表示设备在哪条 I2C 总线上。您甚至没有使用 I2C_DEVICE 宏，但这是您应该传递给 ioctl 调用的内容（例如 ioctl(file, I2C_SLAVE, I2C_DEVICE);），它应该是您想要的设备的 I2C 地址访问（例如 0x5D 用于时钟发生器）而不是 0x00。

我也认为你的reads/writes不正确。一旦你通过 open() 和 ioctl() 指定了总线和设备，你就不需要再担心这些了。您只需要担心要访问的寄存器（如果您的 I2C 设备使用寄存器）和实际数据。

要写入您的 I2C 设备，假设它使用一个字节的寄存器，写入两个字节的缓冲区：第一个是寄存器，第二个是您要写入的值：

bool i2cdev_byte_write(int file, uint8_t reg, uint8_t val)
{
    uint8_t bytes[2];

    bytes[0] = reg;
    bytes[1] = val;

    /* Write the register followed by the value */
    if (write(file, bytes, 2) != 2)
        return false;

    return true;
}

要从您的 I2C 设备读取，假设它使用一个字节的寄存器，写入一个字节的缓冲区（寄存器地址），然后读取一个或多个字节的缓冲区（该寄存器和后续寄存器的值） ):

bool i2cdev_bytes_read(int file, uint8_t reg, unsigned int count, uint8_t *out_buf)
{
    if (!out_buf)
        return false;

    /* Write the register */
    if (write(file, &reg, 1) != 1)
    {
        printf("Failed to write register value\n");
        return false;
    }

    /* Read the specified number of bytes */
    if (read(file, out_buf, count) != count)
    {
        printf("Failed to read from the i2c bus\n");
        return false;
    }

    return true;
}

再次注意，以上所有评论都取决于它是一个使用单字节寄存器地址的 I2C 设备，并且它支持在一次读取多个字节时自动递增寄存器地址。您需要查看 I2C 设备的数据表以确定需要如何访问它。

编辑：这是一个 printf() 新手失败。您不能只尝试 printf 一个字节数组。这不是 printf() 的工作方式。

试试这个：

printf("Buf = [%02X,%02X]\n", buf[0], buf[1]);

此外，正如我在原始回复中所写，您可能需要在读取寄存器内容之前再次写回寄存器地址。

Answer 2

i2c 协议要求您指定设备地址（即 0x00）和寄存器地址。然后您可以将值（在您的情况下为 0x10）写入该寄存器地址。试试这个：

char buf[10];

buf[0] = addr;
buf[1] = [REGISTER ADDRESS];
buf[2] = 0x10;
if(write(file, buf, 3) != 3) {
    printf("Failed to write to bus %s.\n\n", strerror(errno));
}
else {
    printf("Successful write\n");
    printf("Addr: %02x Subaddr: %02x Value: %02x\n\n", buf[0], buf[1], buf[2]);
}

完成此写入后，您应该可以阅读：

if(read(file, buf, 1) != 1) {
    printf("Failed to read from the i2c bus. %s\n\n", strerror(errno));
}
else {
    printf("Successful read\n");
     printf("Value: %02x\n\n", buf[0]);
}

Answer 3

根据设备树，需要提供给IOCtl 的地址是i2cswitch mux 地址。这个地址是0x74，可以在设备树中看到。打开 i2c-0 设备文件对应于设备树中的 i2c0 条目，它是 mux 的父级。写入 EEPROM 时，缓冲区中的第一个字节应该是设备地址，如@AndrewCottrell 所述。这个地址是 0x54。第二个字节应该是你要写入的数据

#define I2C_ADAPTER                 "/dev/i2c-0"
#define I2C_SWITHC_MUX_ADDRESS      0x74
#define DEVICE_ADDRESS              0x54

...

file = open(I2C_ADAPTER, O_RDWR); /* Check for error */
ioctl(file, I2C_SLAVE_FORCE, I2C_SWITHC_MUX_ADDRESS); /* Check for error */

uint8_t reg, value;

reg = DEVICE_ADDRESS;

buf[0] = reg;
buf[1] = value;

write(file, buf, 2); /* Check for error */
read(file, buf, 1); /* Check for error */
/* buf[0] should be value*/

Answer 4

我在从 NTAG 5 boost 组件的内存中读取数据时也遇到了问题，我在查找此问题的原因时发现了此线程。事实上，对于我在组件上执行的每个 I2C 读取，我都会收到“FF”值。我没有在此线程中找到答案，但也许你在 .

中回答了我的问题

写入 I2C 的缓冲区在读取时不返回

Written Buffer to I2C Not Returned when Read

c

linux

embedded

qemu

i2c