RS485:设备的不适当的ioctl

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问题描述

我正在使用以下代码访问RS485从站，但出现错误:

I am using the following code to access the RS485 slave but I get the error:

我的代码如下:

#include <linux/serial.h>
#include <sys/ioctl.h>


    int fd = open ("/dev/ttyUSB0", O_RDWR);
    if (fd < 0) {
        printf("Error Opening\n");
        exit(0);
    }

    struct serial_rs485 rs485conf;

    /* Enable RS485 mode: */
    rs485conf.flags |= SER_RS485_ENABLED;

    /* Set logical level for RTS pin equal to 1 when sending: */
    rs485conf.flags |= SER_RS485_RTS_ON_SEND;

    /* set logical level for RTS pin equal to 0 after sending: */
    rs485conf.flags &= ~(SER_RS485_RTS_AFTER_SEND);

    /* Set rts delay before send, if needed: */
    rs485conf.delay_rts_before_send = 0;

    /* Set rts delay after send, if needed: */
    rs485conf.delay_rts_after_send = 0;

    /* Set this flag if you want to receive data even whilst sending data */
    rs485conf.flags |= SER_RS485_RX_DURING_TX;

    if (ioctl (fd, TIOCSRS485, &rs485conf) < 0) {
        fprintf( stderr, "Error reading ioctl port (%d): %s\n",  errno, strerror( errno ));
        exit(0);
    }

    //TODO read and write

    /* Close the device when finished: */
    if (close (fd) < 0) {
        fprintf( stderr, "Error closing device connection (%d): %s\n",  errno, strerror( errno ));
    }

我从 https://www.kernel获取了源代码.org/doc/Documentation/serial/serial-rs485.txt .我正在树莓派上开发应用程序，并使用Quad RS232-HS芯片连接到FTDI USB串行设备.错误的根源可能是什么?\

I took the source code from https://www.kernel.org/doc/Documentation/serial/serial-rs485.txt. I am developing my application on the raspberry pi and am connected to the FTDI USB Serial device using Quad RS232-HS chip. What might be the source of the error?\

当我连接USB设备时，输出

When USB I connect the USB device, output for

如下:

[16865.640038] usb 3-2: new high-speed USB device number 10 using xhci_hcd
[16865.780365] usb 3-2: New USB device found, idVendor=0403, idProduct=6011
[16865.780367] usb 3-2: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[16865.780369] usb 3-2: Product: Quad RS232-HS
[16865.780370] usb 3-2: Manufacturer: FTDI
[16866.377940] usbcore: registered new interface driver usbserial
[16866.377969] usbcore: registered new interface driver usbserial_generic
[16866.377994] usbserial: USB Serial support registered for generic
[16866.384018] usbcore: registered new interface driver ftdi_sio
[16866.384045] usbserial: USB Serial support registered for FTDI USB Serial Device
[16866.384203] ftdi_sio 3-2:1.0: FTDI USB Serial Device converter detected
[16866.384247] usb 3-2: Detected FT4232H
[16866.384373] usb 3-2: FTDI USB Serial Device converter now attached to ttyUSB0
[16866.384399] ftdi_sio 3-2:1.1: FTDI USB Serial Device converter detected
[16866.384431] usb 3-2: Detected FT4232H
[16866.384727] usb 3-2: FTDI USB Serial Device converter now attached to ttyUSB1
[16866.384751] ftdi_sio 3-2:1.2: FTDI USB Serial Device converter detected
[16866.384786] usb 3-2: Detected FT4232H
[16866.384897] usb 3-2: FTDI USB Serial Device converter now attached to ttyUSB2
[16866.384917] ftdi_sio 3-2:1.3: FTDI USB Serial Device converter detected
[16866.384950] usb 3-2: Detected FT4232H
[16866.385385] usb 3-2: FTDI USB Serial Device converter now attached to ttyUSB3

推荐答案

正如@Richard Chambers在评论中所提到的，您正在使用未初始化的结构.你应该做

As mentioned in the comment by @Richard Chambers you are using the structure uninitialised. You should do

struct serial_rs485 rs485conf = {0};

但是，正如所讨论的那样，并不能解决问题.

However, as discussed that didn't solve the problem.

引用您引用的内核文档

但是，该设备具有专用于此的称为TXDEN的引脚.引用数据表部分4.3.3

However this device has a dedicated pin called TXDEN for that. Quoting from the Data sheet section 4.3.3

您会看到RS232输出未在RS485中连接的RTS/DTR，这与RTS变为TXDEN且需要驾驶员干预的设备形成对比.

and you can see that the RS232 outputs RTS / DTR not connected in RS485, this is in contrast to devices where RTS becomes TXDEN which would require an intervention by the driver.

如果我们分开struct serial_rs485，我们可以看到它主要是为了控制RTS.由于该设备具有专用的TXDEN引脚，因此这些控制字段无关.

If we pick apart struct serial_rs485 we can see that it is mostly about controlling RTS for this purpose. Since this device has a dedicated TXDEN pin, those control fields are irrelevant.

此结构中使用的另一个标志:

Another flag that is used in this structure:

  /* Set this flag if you want to receive data even whilst sending data */
rs485conf.flags |= SER_RS485_RX_DURING_TX;

是的，看看电路，您在线路上输入的内容也会收到.看来您无法关闭它. RS485是多点发送的，因此您应该过滤掉未发送给您的消息.这些消息中的某些消息可能源于您这一事实无关紧要.

And yes looking at the circuit, what you put out on the line you will also receive. Looks like you cannot turn that off. RS485 is multidrop, so you should be filtering out messages that were not addressed to you anyway. The fact that some of those messages may have originated from you doesn't matter.

最后(首先)，我们有这个

Finally (and firstly) we have this

/* Enable RS485 mode: */
rs485conf.flags |= SER_RS485_ENABLED;

这实际上是在说启用所有受此结构控制的特定于RS485的内容".除了我们只是使所有这些东西无关紧要之外，因此启用它没有任何作用.

That's really saying "enable all the RS485-specific stuff that's controlled by this structure". Except that we've just made all that stuff irrelevant, so enabling it has no effect.

这就是为什么未为该UART实现ioctl的原因.

This is why the ioctl is not implemented for that UART.

您有很多选择，这些只是建议，因此请选择适合您的

You have a number of options, these are just suggestions so pick what suits you

删除不需要的初始化代码部分
有条件地进行编译#if RS485_IOCTLS
有条件地运行
处理该errno值ENOTTY表示，在这种情况下，不需要ioctl，实际上您可以像没有错误一样进行操作

Delete this section of the initializtion code as it's not needed
Compile it conditionally #if RS485_IOCTLS
Run it conditionally
Treat that errno value ENOTTY as indicating that, in this context the ioctl was not required and you can in fact proceed as if there was no error

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