Multiple Serial devices over USB on Raspberry Pi

2020-02-27T14:51:03.834000Z

Originally created by: KevinR

After writing the instruction, I've checked the forum and have seen, that there is already an instruction available:

Check this link:
l viewtopic.php?f=23&t=6247&start=30 l

Multiple Serial devices over USB on Raspberry Pi

2020-02-27T14:51:02.064000Z

Originally created by: KevinR

Hi pdoubleu,

you can bound the COM-Port Number to the USB-Port, by specifying the USB-port path.
And then you can use the COM-Port numbers for a single motor, for example COM-Port number 1 for motor 1 and COM-Port number 2 for motor 2 and so on.

I've got a little instruction for this:

First let's identify the name of the interface, by using the attribute ATTRS(interface}.
So we can make sure that only a device, with the correct interface name, is "linked".

To check the attributes of a plugged-in device, use following code:

 udevadm info --name /dev/ttyUSB0 --attribute-walk

It will show you the information, from parent device to parent device. So the first info should be something like this:

 
 looking at device '/devices/platform/soc/3f980000.usb/usb1/1-1/1-1.4/1-1.4:1.0/ttyUSB0/tty/ttyUSB0':
    KERNEL=="ttyUSB0"
    SUBSYSTEM=="tty"
    DRIVER==""

So go ahead and look for the attribute "ATTRS{interface}"
This attribute gives you the name of the plugged-in USB extension.

  looking at parent device '/devices/platform/soc/3f980000.usb/usb1/1-1/1-1.4/1-1.4:1.0':
    KERNELS=="1-1.4:1.0"
    SUBSYSTEMS=="usb"
    DRIVERS=="ftdi_sio"
    ATTRS{authorized}=="1"
    ATTRS{bAlternateSetting}==" 0"
    ATTRS{bInterfaceClass}=="ff"
    ATTRS{bInterfaceNumber}=="00"
    ATTRS{bInterfaceProtocol}=="ff"
    ATTRS{bInterfaceSubClass}=="ff"
    ATTRS{bNumEndpoints}=="02"
    ATTRS{interface}=="<Name of the device>"
    ATTRS{supports_autosuspend}=="1"

Now you can create a udev rule, by editing your udev rule file and add:

SUBSYSTEM=="tty", KERNEL=="ttyUSB*", KERNELS=="1-1.4:1.0", ATTRS{interface}=="<Name of the device>", SYMLINK+="ttyRS0"

The Parameter is the fixed path of the usb-port.

So this device will now always have the COM-Port number 1. If you want to add another device and you want to skip Com-Port number 2, you can use following rule:

1.) Find out the name of the interface again
2.) Check the USB-Port path.
3.) add your rule as you want

SUBSYSTEM=="tty", KERNEL=="ttyUSB*", KERNELS=="1-1.3:1.0", ATTRS{interface}=="<Name of the other device>", SYMLINK+="ttyRS2"

What we also did, is to create a SYMLINK. This will avoid further problems, in case of that you're using different devices, like "ttyAMA" or something else. Because as far as I know, you can specify only one Device file name in the codesyscontrol config file, so you can avoid further troubles.

In case of that, you have a totally different device, you can also use other devices.
Example:

SUBSYSTEM=="tty", KERNEL=="ttyAMA*", KERNELS=="1-1.2:1.0", ATTRS{interface}=="<Name of the ttyAMA device>", SYMLINK+="ttyRS3"

The CODESYSControl_User.cfg should look like this:

[SysCom]
Linux.Devicefile=/dev/ttyRS

I think you don't need the last parameter "_:=...". But I'm not sure.

I hope this little instruction helps you.

Let me know if I missed something.

PS: I think this post should be moved to the raspberry pi forum category.

Multiple Serial devices over USB on Raspberry Pi

2020-02-27T14:51:01.502000Z

Hi everyone,

Unfortunately I havent found anything regarding my question using the search function.

Here is my question:

I want to connect 4 serial devices to the 4 USB ports on Raspi. All 4 devices are exactely the same (Roboclaw motor controller).
Using udev rules I am able to give all of them reproducable names, even if I disconnect and reconnect them, so thats all fine.

To use the serial USB in codesys I know that I need to add the following lines to CODESYSControl_User.cfg:

[SysCom]
Linux.Devicefile=/dev/ttyUSB
portnum:=COM.SysCom.SYS_COMPORT1

After this I am able to control the devices vial the CAA serial library.

My question is now if there is a way to assign each Motorcontroller to a specific comport, so that I can decide which motorcontroller to "speak" without sending every command to each motor?

Thank for any help!

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