Baby LIN

Support for the LIN protocol is provided via the BabyLIN™ USB adapter. The adapter connects to the RT host via a USB port and provides the functionality of either a LIN master node or LIN slave node.

Similar to the CAN bus, the LIN protocol allows transfer of 8 byte message associated to an ID. The ID is 1 byte and the values for the ID are between 0 and 63.

RTDB items can be mapped to multi bit/byte fields defined on the 8 byte buffer payload.

Reference Information BabyLIN

I/O Card Model Number

CS-Baby-LIN-x.

I/O Driver Model Number

Provided via kernel usbserial.

I/O Module License:

ICS-SWB-1252.

NODE Configuration

In LIN terminology, LIN nodes either publish a frame or subscribe to a frame. A frame publisher is responsible for generating the frame content while a frame subscriber is interested in receiving the specific frame to read its content. Master and slave nodes can both be publisher and subscriber of frames. However, there can only be a single publisher of a specific frame on a LIN network. Buttons Expand All Expands the hierarchy tree showing board configuration. Collapse All Collapses the hierarchy tree showing the board configuration to show only the channel nodes. New ID Adds a new LIN frame ID under the selected subscriber/publisher branch. Delete Deletes the selected frame ID and everything, including mappings, below it. Speed bits/s Select the speed at which this Baby LIN will connect to the LIN network. Auto detect can only be specified for a slave node. LIN Master Specify that this BabyLIN node is a LIN master. OS Device Specify the OS device to use for this specific Baby LIN device. Support to access the device is provided by the RedHawk kernel via the usbserial device. Typical name for the OS device is /dev/ttyUSBx where x is a number starting at 0 for the first Baby LIN device. This number may vary if you have other USB serial devices installed in your system. The ttyUSBx name must be unique for each Baby LIN device, when multiple Baby LIN devices are being used. Note: The device name can change if the system configuration changes. For example, when a new USB device is installed.

LIN Frame Configuration

Frame ID The message identifier. This is a 6-bit value, The maximum value allowed is 63. FIFO Specifies that the message is transmitted as soon as it changes. For output messages only. TX on change When a message is defined as FIFO and TX on change is set, the output frame is sent as soon as the content change, when TX on change is not set, the frame is only sent on user request via an API call. Sched Rate (ms) The rate in milliseconds at which transmission/polling is scheduled. Contrary to the CAN network. Input messages (subscriber) need to be retrieved from the LIN slaves by the master node. Thus, the schedule rate must also be specified for subscribed messages. Message Length The number of bytes in the message (maximum 8). LIN Version The LIN protocol version for the frame. Either 1.2/1.3 or 2.0, The protocol will determine how the checksum on the message content is calculated. New Field Adds a new data field for RTDB mapping to the selected frame. Delete Deletes the selected field including mappings.

Message Field Definition

You map RTDB item to a LIN message by creating new fields byte/bit fields within the frame. Each individual field has a raw data type - Packed,int,float,etc. that can be map to individual RTDB items by selecting the field and clicking on the checkbox next to the item name in the right panel. Raw Type How to interpret the raw bits of the field. Packed Integer bit field. Location is specified by the Bit setting. char One-byte integer. Location is specified by the Byte setting. short Two-byte integer. Location is specified by the Byte setting. int Four-byte integer. Location is specified by the Byte setting. float Four-byte floating-point number. Location is specified by the Byte setting. double Eight-byte floating-point number. Location must be specified as 0 by the Byte setting. Byte (offset) Byte offset within the 8-byte data of the non-bit field data. Bit (offset:size) Bit offset and number of bits to reserve for the field within the 64-bit data of the message. Big Endian Interprets the bytes as most significant byte first.

Assigning BabyLIN Device Node

To avoid the possibility of the BabyLIN USB device assignment changing upon reboot, you can use udev to specify the device node that is created in the /dev directory. The following steps describe how to automatically generate a symbolic link to /dev/ttyUSB0 from /dev/babyLIN0. If you have more BabyLIN devices, simply change the device number suffix as appropriate.

• Plug the BabyLIN device into the USB port of choice.
• Execute the following at the terminal to identify unique attributes of the device:

  udevadm info --attribute-walk --path=/sys/bus/usb-serial/devices/ttyUSB0

  
  The output is as follows:

  /* snip */
  
  looking at device '/devices/pci0000:00/0000:00:12.0/usb4/4-3/4-3:1.0/ttyUSB0':
  KERNEL=="ttyUSB0"
  SUBSYSTEM=="usb-serial"
  DRIVER=="cp210x"
  ATTR{port_number}=="0"
  
  looking at parent device '/devices/pci0000:00/0000:00:12.0/usb4/4-3/4-3:1.0':
  KERNELS=="4-3:1.0"
  SUBSYSTEMS=="usb"
  DRIVERS=="cp210x"
  ATTRS{bInterfaceClass}=="ff"
  ATTRS{modalias}=="usb:v10C4p81E2d0201dc00dsc00dp00icFFisc00ip00"
  ATTRS{bInterfaceSubClass}=="00"
  ATTRS{bInterfaceProtocol}=="00"
  ATTRS{bNumEndpoints}=="02"
  ATTRS{supports_autosuspend}=="1"
  ATTRS{bAlternateSetting}==" 0"
  ATTRS{bInterfaceNumber}=="00"
  ATTRS{interface}=="Baby-LIN LIN-Bus Interface"
  
  looking at parent device '/devices/pci0000:00/0000:00:12.0/usb4/4-3':
  KERNELS=="4-3"
  SUBSYSTEMS=="usb"
  
  /* snip */

• Add a file called 98-ttyUSB.rules to /etc/udev/rules.d/. The contents of this file are as follows:

  KERNEL=="ttyUSB*",KERNELS=="4-3",SYMLINK+="babyLIN0"
  KERNEL=="ttyUSB*",KERNELS=="4-4",SYMLINK+="babyLIN1"

  
  The first line references two unique identifiers underlined in the udevadm output. So, the next time the system is booted, udev will ensure that a symbolic link called /dev/babyLIN0 is created to /dev/ttyUSB0, which is plugged into the 4-3 USB port.
  The second line shows an example of referencing a second babyLIN device plugged into the 4-4 USB port.

   

• Unplug the BabyLIN device (remember what port it was plugged into). Remove the device driver (rmmod usbserial cp210x).
  Replug the device in the correct port. The device driver should reload automatically. You should also see messages in dmesg regarding the device.
  If your rules are set up correctly, executing ls -ltrah /dev/baby* will result in an output similar to the following:

  lrwxrwxrwx 1 root root 7 Sep 11 13:15 /dev/babyLIN0 -> ttyUSB0
  lrwxrwxrwx 1 root root 7 Sep 11 13:15 /dev/babyLIN1 -> ttyUSB1

  
  If the rules are not loaded automatically, try:

  udevadm control --reload-rules && udevadm trigger

  
  For more information about udev, type man udev.

   

• In the BabyLIN I/O mapping, update the OS Device field to babyLIN0 to use the symlink you created.

Synchronous I/O Task: babylinout

This process packs all BabyLIN raw output values corresponding to LIN output frames and places them in the BabyLIN output FIFO queue. The process will not queue a request into the FIFO queue if the raw LIN message is unchanged since the last test cycle.

The FIFO queue is read by the babylinasyncio asynchronous task which in turns reads from and writes to the Baby LIN device.