读取时不会返回I2C写入的缓冲区

我写入后尝试从I2C总线上的存储单元读取一个值.当我在终端中运行它时,我得到奇怪的输出.

这是我的计划

    #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,这些街区看起来更像钻石内的问号.我不确定在ASCII中对应什么.

为什么我不读回0x10,这是我最初写入的地址字节后的第二个字节?

根据第一组答案,这里是更新的代码:

#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addr时,无论argv [2]是什么,我都会得到FF,FF,FF作为输出.以下是设备树文件的适用部分.请注意,这是模拟的,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>;
            };
        };
    };
};

以下是几个示例测试

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

这是我的第三次尝试的程序.在记下答案中的笔记之后,我写了这篇文章

#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,即便如此,我也遇到了同样的错误.

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

解决方法:

编辑2:我认为你可能没有正确设置你的I2C设备地址.您拥有的I2C_ADAPTER(“/ dev / i2c-0”)表示设备所在的I2C总线.您甚至没有使用I2C_DEVICE宏,但这应该是您应该传递给ioctl调用的内容(例如ioctl(文件,I2C_SLAVE,I2C_DEVICE);)它应该是您要访问的设备的I2C地址(例如0x5D)对于时钟发生器而不是0x00.

我也认为你的读/写不正确.一旦你通过open()和ioctl()指定了总线和设备,你就不用再担心了.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,上述所有注释都取决于它是使用单字节寄存器地址的I2C器件,并且它支持在一次读取多个字节时自动递增寄存器地址.您需要检查I2C设备的数据表,以确切地确定它是如何被访问的.

编辑:这是一个printf()新手失败.你不能只尝试printf一个字节数组.这不是printf()的工作原理.

试试这个:

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

另外,正如我在原始响应中所写的那样,在读取寄存器内容之前,您可能需要再次将寄存器地址写回.

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