TWAI Network Example

This example demonstrates TWAI (Two-Wire Automotive Interface) network communication using the ESP-IDF TWAI driver. It consists of two programs that showcase different aspects of TWAI bus communication.

Overview

Programs

• twai_sender: Sends periodic heartbeat messages and large data packets
• twai_listen_only: Monitors specific message ID using a filter

Key Features

• Event-driven message handling with callbacks
• Message filtering using acceptance filters in listen-only mode
• Single/Burst data transmission and reception
• Real-time bus error and node status reporting

Hardware Setup

Wiring

For multi-device testing:

1. Connect TWAI transceivers to each ESP32xx
2. Wire TWAI_H and TWAI_L between all devices using line topology
3. Add 120Ω termination resistors at both ends of the bus

For single-device testing, enable self_test mode in the sender.

GPIO Configuration

The GPIO pins can be configured using menuconfig:

idf.py menuconfig

Navigate to: Example Configuration → Configure the following:

• TWAI TX GPIO Num: GPIO pin for TWAI TX
• TWAI RX GPIO Num: GPIO pin for TWAI RX

Default configuration:

#define TWAI_TX_GPIO    GPIO_NUM_4
#define TWAI_RX_GPIO    GPIO_NUM_5  
#define TWAI_BITRATE    1000000     // 1 Mbps

Message Types

Building and Running

Build each program (sender, listen_only):

Enter the sub-application directory and run:

idf.py set-target esp32 build flash monitor

Expected Output

Sender

===================TWAI Sender Example Starting...===================
I (xxx) twai_sender: TWAI Sender started successfully
I (xxx) twai_sender: Sending messages on IDs: 0x100 (data), 0x7FF (heartbeat)
I (xxx) twai_sender: Sending heartbeat message: 1234567890
I (xxx) twai_sender: Sending packet of 1000 bytes in 125 frames

Listen-Only Monitor

===================TWAI Listen Only Example Starting...===================
I (xxx) twai_listen: Buffer initialized: 200 slots for burst data
I (xxx) twai_listen: TWAI node created
I (xxx) twai_listen: Filter enabled for ID: 0x100 Mask: 0x7F0
I (xxx) twai_listen: TWAI start listening...
I (xxx) twai_listen: RX: 100 [8] 0 0 0 0 0 0 0 0
I (xxx) twai_listen: RX: 100 [8] 1 1 1 1 1 1 1 1

Implementation Details

Message Buffering

Each program uses a buffer pool to handle incoming messages efficiently:

• Sender: Small buffer for transmission completion tracking
• Listen-Only: 100-slot buffer for monitoring filtered traffic

Operating Modes

• Normal Mode (Sender): Participates in bus communication, sends ACK frames
• Listen-Only Mode (Monitor): Receives filtered messages without transmitting anything

Message Filtering

The listen-only monitor uses hardware acceptance filters to receive only specific message IDs:

twai_mask_filter_config_t data_filter = {
    .id = TWAI_DATA_ID,
    .mask = 0x7F0,      // Match high 7 bits of the ID, ignore low 4 bits
    .is_ext = false,    // Receive only standard ID
};

Error Handling

• Bus error logging and status monitoring

Configuration

Customizing Buffer Sizes

Adjust buffer sizes in each program as needed:

#define POLL_DEPTH  200  // Listen-only buffer size

Changing Message IDs

Update the message ID definitions:

#define TWAI_DATA_ID       0x100
#define TWAI_HEARTBEAT_ID  0x7FF

Use Cases

This example is suitable for:

• Learning TWAI bus communication
• Testing TWAI network setups
• Developing custom TWAI protocols
• Bus monitoring and debugging
• Prototyping automotive communication systems

Troubleshooting

No Communication

• Check GPIO pin connections
• Verify bitrate settings match between devices
• Ensure proper bus termination

Buffer Overflows

• Increase buffer size (POLL_DEPTH)
• Reduce bus message transmission rate
• Optimize message processing code

Bus Errors

• Check physical bus wiring
• Verify termination resistors (120Ω at each end)
• Monitor error counters with twai_node_get_info()