I2C_IIC

at24cxx驱动包中读操作中有错误

发布于 2019-12-06 11:40:52 浏览：2667 订阅该版

最近做项目用到的RT THREAD 在做I2C存储的时候使用EVN工具
menuconfig 
RT-Thread online packages  ---> 
peripheral libraries and drivers  ---> at24cxx: eeprom at24cxx driver library.  --->

下载了at24cxx的驱动包，打开驱动包看了下程序源码发现一些问题

我们看下驱动包里读一个字节的源代码
```uint8_t at24cxx_read_one_byte(struct rt_i2c_bus_device *bus, uint16_t readAddr)
{
    rt_uint8_t buf[2];
    rt_uint8_t temp;
#if        (EE_TYPE > AT24C16)  
    buf[0] = (uint8_t)(readAddr>>8);        
    buf[1] = (uint8_t)readAddr;
    if (rt_i2c_master_send(bus, AT24CXX_ADDR, 0, buf, 2) == 0) 
#else
    buf[0] = readAddr;
    if (rt_i2c_master_send(bus, AT24CXX_ADDR, 0, buf, 1) == 0)
#endif        
    {
        return -RT_ERROR;
    }
    read_regs(bus, 1, &temp);
    return temp;
}```程序调用rt_i2c_master_send对I2C从机写寄存器地址，调用read_regs从I2C从机读一个字节（两个子函数源代码如下）
rt_i2c_master_send源代码
```rt_size_t rt_i2c_master_send(struct rt_i2c_bus_device *bus,
                             rt_uint16_t               addr,
                             rt_uint16_t               flags,
                             const rt_uint8_t         *buf,
                             rt_uint32_t               count)
{
    rt_err_t ret;
    struct rt_i2c_msg msg;

msg.addr  = addr;
    msg.flags = flags & RT_I2C_ADDR_10BIT;
    msg.len   = count;
    msg.buf   = (rt_uint8_t *)buf;

ret = rt_i2c_transfer(bus, &msg, 1);

return (ret > 0) ? count : ret;
}```
read_regs源代码
```static rt_err_t read_regs(struct rt_i2c_bus_device *bus, rt_uint8_t len, rt_uint8_t *buf)
{
    struct rt_i2c_msg msgs;

msgs.addr = AT24CXX_ADDR;
    msgs.flags = RT_I2C_RD;
    msgs.buf = buf;
    msgs.len = len;

if (rt_i2c_transfer(bus, &msgs, 1) == 1)
    {
        return RT_EOK;
    }
    else
    {
        return -RT_ERROR;
    }
}```这里我们看到rt_i2c_master_send和read_regs最终都是调用rt_i2c_transfer这个函数进行的数据传输，我们在看下rt_i2c_transfer的源代码
```static rt_size_t i2c_bit_xfer(struct rt_i2c_bus_device *bus,
                              struct rt_i2c_msg         msgs[],
                              rt_uint32_t               num)
{
    struct rt_i2c_msg *msg;
    struct rt_i2c_bit_ops *ops = bus->priv;
    rt_int32_t i, ret;
    rt_uint16_t ignore_nack;

bit_dbg("send start condition ");
 i2c_start(ops);
 for (i = 0; i < num; i++)
 {
 msg = &msgs*;
 ignore_nack = msg->flags & RT_I2C_IGNORE_NACK;
 if (!(msg->flags & RT_I2C_NO_START))
 {
 if (i)
 {
 i2c_restart(ops);
 }
 ret = i2c_bit_send_address(bus, msg);
 if ((ret != RT_EOK) && !ignore_nack)
 {
 bit_dbg("receive NACK from device addr 0x%02x msg %d ",
 msgs*.addr, i);
 goto out;
 }
 }
 if (msg->flags & RT_I2C_RD)
 {
 ret = i2c_recv_bytes(bus, msg);
 if (ret >= 1)
 bit_dbg("read %d byte%s ", ret, ret == 1 ? "" : "s");
 if (ret < msg->len)
 {
 if (ret >= 0)
 ret = -RT_EIO;
 goto out;
 }
 }
 else
 {
 ret = i2c_send_bytes(bus, msg);
 if (ret >= 1)
 bit_dbg("write %d byte%s ", ret, ret == 1 ? "" : "s");
 if (ret < msg->len)
 {
 if (ret >= 0)
 ret = -RT_ERROR;
 goto out;
 }
 }
 }
 ret = i;

out:
 bit_dbg("send stop condition ");
 i2c_stop(ops);

return ret;
}```在rt_i2c_transfer源代码的最后我们可以看到 该函数在最后对I2C总线发送了停止位（i2c_stop(ops);）那么问题来了 at24cxx的驱动包读一个字节调用了两次rt_i2c_transfer，相当于每次调用就发送一个停止位，这明显与I2C通讯机制不一致。

我们都知道I2C读一个字节数据的的流程是（大概流程 没写ACK NACK）
起始位  --  器件地址+写  --  寄存器地址 -- 起始位 --  器件地址+读  --  送机发送数据  --  停止位

而 at24cxx的驱动包读一个字节的流程变成了
起始位  --  器件地址+写  --  寄存器地址 -- 停止位  --  起始位 --  器件地址+读  --  送机发送数据  --  停止位

很明显这是错误，不明白这么明显有错误的包官方为什么收录了。

5 个回答

tyustli 2019-12-07

这家伙很懒，什么也没写！

sync 2020-03-11

这家伙很懒，什么也没写！

Acuity 2020-04-16

这家伙很懒，什么也没写！

ArvinLv 2020-04-16

这家伙很懒，什么也没写！

>1、读函数应该调原始接口
>
>2、写函数没有加入页写算法，效率有点低。

---

static rt_size_t imxrt_i2c_mst_xfer(struct rt_i2c_bus_device *bus,
                                    struct rt_i2c_msg msgs[],
                                    rt_uint32_t num)
{
    struct imxrt_i2c_bus *imxrt_i2c;
    rt_size_t i;
    RT_ASSERT(bus != RT_NULL);
    imxrt_i2c = (struct imxrt_i2c_bus *) bus;

imxrt_i2c->msg = msgs;
    imxrt_i2c->msg_ptr = 0;
    imxrt_i2c->msg_cnt = num;
    imxrt_i2c->dptr = 0;

for (i = 0; i < num; i++)
 {
 if (imxrt_i2c->msg[i].flags & RT_I2C_RD)
 {
 if (LPI2C_MasterStart(imxrt_i2c->I2C, imxrt_i2c->msg[i].addr, kLPI2C_Write) != kStatus_Success)
 {
 i = 0;
 break;
 }

while (LPI2C_MasterGetStatusFlags(imxrt_i2c->I2C) & kLPI2C_MasterNackDetectFlag)
            {
            }

if (LPI2C_MasterRepeatedStart(imxrt_i2c->I2C, imxrt_i2c->msg[i].addr, kLPI2C_Read) != kStatus_Success)
            {
                i = 0;
                break;
            }

if (LPI2C_MasterReceive(imxrt_i2c->I2C, &imxrt_i2c->msg[i].buf, imxrt_i2c->msg[i].len) != kStatus_Success)
            {
                i = 0;
                break;
            }
        }
        else
        {
            if (LPI2C_MasterStart(imxrt_i2c->I2C, imxrt_i2c->msg[i].addr, kLPI2C_Write) != kStatus_Success)
            {
                i = 0;
                break;
            }

while (LPI2C_MasterGetStatusFlags(imxrt_i2c->I2C) & kLPI2C_MasterNackDetectFlag)
            {
            }

if (LPI2C_MasterSend(imxrt_i2c->I2C, imxrt_i2c->msg[i].buf, imxrt_i2c->msg[i].len) != kStatus_Success)
            {
                i = 0;
                break;
            }

if (LPI2C_MasterWaitForTxFifoAllEmpty(imxrt_i2c->I2C) != kStatus_Success)
            {
                i = 0;
                break;
            }
        }
    }

if (LPI2C_MasterStop(imxrt_i2c->I2C) != kStatus_Success)
    {
        i = 0;
    }

imxrt_i2c->msg = RT_NULL;
    imxrt_i2c->msg_ptr = 0;
    imxrt_i2c->msg_cnt = 0;
    imxrt_i2c->dptr = 0;

return i;
}
这个imxrt_i2c_mst_xfer函数是RTT的抽象层函数，但是从这个函数来看读一个字节的流程变成了
起始位  --  器件地址+写--  起始位 --  器件地址+读  --  送机发送数据  --  停止位；
理论上在写完器件地址后应该写寄存器地址啊，这个怎么没了？感觉这个驱动有问题啊？