CAN

• Uses CSMA/CD method and bitwise contention to sense the bus at the bit-level and transmit the message.
• Each message is assigned a priority. Messages with the highest priority always control the bus arbitration. Since arbitration is based on bits, there are dominant and recessive bit levels.
• Any node can transmit at any time, no primary-secondary nodes.
• All the data is transmitted through two (differential pair) lines: CAN_H and CAN_L line.
• CAN nodes are synchronized using bit-synchronization where each bit time is divided in to four segments of time quanta.
• Facilitates communication between multiple nodes through a message-based protocol, eliminating the need for extensive wiring.
• Ensures data security with error management including detection, signaling, and correction.

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CAN features

• Multicontroller priority-based bus access
• Nondestructive content-based arbitration
• Broadcast through all-frame transfer
• Multicast frame transfer by acceptance filtering
• Remote data request
• Configuration flexibility
• Network-wide data consistency
• Error detection and error signaling
• Automatically retransmits frames that lose arbitration, lack acknowledgment, or encounter errors during transmission
• Identifies differences between temporary node errors and permanent node failures, and the automatic deactivation of faulty nodes

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CAN architecture

Figure : CAN architecture

Figure : CAN software stack

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CAN APIs

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CAN samples and tools

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CAN analyzer - PCAN-USB FD

• PCAN-View GUI tool
  • Provides easy ways to sniff and send CAN packets as per-user needs.
  • Monitors and debugs CAN packets during development and testing.
• PCAN-USB FD interface
  • Enables a simple connection to CAN FD and CAN networks.
  • Compact plastic casing suitable for mobile applications.
  • Galvanic isolation of up to 500 V decouples the PC from the CAN bus.
• CAN FD standard
  • Characterized by higher bandwidth for data transfer.
  • Allows transmission of up to 64 data bytes per CAN FD frame (instead of 8).
  • Supports bit rates up to 12 Mbit/s.
  • Downward compatible with the CAN 2.0 standard.
  • CAN FD nodes can be inserted into existing CAN networks without CAN FD extensions.

1. Connect to the DB9 connector.
   • The PCAN has a DB9 connector on which any standard DB9 connector can be plugged in.
2. Connect to the Qualcomm device.
   • Pull out the CAN_H, CAN_L, and GND lines.
   • Connect these lines to the two terminal-resistors of 120 Ω.
3. Connect CAN_H, CAN_L, and Ground.

Figure : CAN connections

4. Connect an external terminating resistor.

Figure : CAN terminating resistor

Figure : CAN USB FD, external resistor, and device connection

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Bringup CAN interface

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Send and receive data

• Send data with 11‑bit ID
  cansend can0 7AF#11.22.33.44.55.66.aa.ff
  
• Send data with 29‑bit ID
  cansend can0 111FFFFF#aa.00.cc.aa.33.61.aa.ab
  
• View the current incoming data on can0 node
  candump can0
  

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Configure CAN interface

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Initialize hardware

static struct spi_driver mcp251xfd_driver = {
    .driver = {
        .name = DEVICE_NAME,
        .pm = &mcp251xfd_pm_ops,
        .of_match_table = mcp251xfd_of_match,
    },
    .probe = mcp251xfd_probe,
    .remove = mcp251xfd_remove,
    .id_table = mcp251xfd_id_table,
};
 
static int mcp251xfd_probe(struct spi_device *spi)
{
    struct net_device *ndev;
    struct mcp251xfd_priv *priv;
[..]
ndev = alloc_candev(sizeof(struct mcp251xfd_priv),
                MCP251XFD_TX_OBJ_NUM_MAX);
    if (!ndev)
        return -ENOMEM;
 
    SET_NETDEV_DEV(ndev, &spi->dev); // The SPI node is set as the parent node to the network device. 
 
    ndev->netdev_ops = &mcp251xfd_netdev_ops;
[..]
    err = mcp251xfd_register(priv);
};

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Debug CAN issues

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CAN examples