TWAI Bus-Off Recovery Example

This example demonstrates how to recover a TWAI node from a Bus-Off error condition and resume communication. The recovery is triggered by physically inducing bus errors and handled using the ESP TWAI on-chip driver with callback support.

How It Works

1. Initialize and start the TWAI node using esp_twai_onchip.
2. Transmit a few TWAI frames in normal operation.
3. Manually trigger bit errors by either:
   • Briefly disconnecting the TX or RX connection
   • Briefly short-circuiting the TWAI H and TWAI L lines
4. When the node enters the Bus-Off state, an error recovery process will automatically initiated.
5. Once recovered, resume normal transmission.

Hardware Requirements

• An ESP32xx chip with TWAI peripheral support
• External TWAI transceiver (e.g., TJA1050, MCP2551, or similar)
• TWAI bus setup with proper termination resistors

Pin Configuration

Modify TX_GPIO_NUM and RX_GPIO_NUM in the twai_recovery_main.c if needed. Connect these pins to your TWAI transceiver's TX and RX pins respectively.

#define TX_GPIO_NUM         GPIO_NUM_4
#define RX_GPIO_NUM         GPIO_NUM_5

Manual Error Triggering

To trigger bus errors and test the recovery mechanism, you can use either of these methods:

1. Connection Disruption: Briefly disconnect the TX or RX wire between the ESP32 and the TWAI transceiver while frames are being transmitted.

2. Bus Short Circuit: Briefly short-circuit the TWAI H and TWAI L lines on the bus. This simulates a bus fault condition.

⚠️ Important: The disconnection or short-circuit should be brief enough to trigger bus error messages in the log output. Too long may cause permanent damage to the transceiver or affect other nodes on the bus.

Build and Flash

idf.py set-target esp32 build
idf.py -p PORT flash monitor

Example Output

install twai success
node started

sending frame 0, please trigger error during sending
sending frame 1, please trigger error during sending

...
sending frame 4, please trigger error during sending
// Manually trigger error here (disconnect TX/RX or short H/L)
bus error: 0x2
state changed: error_active -> error_warning

...
sending frame 9, please trigger error during sending
// Trigger error again
bus error: 0x2
state changed: error_passive -> bus_off

node offline, start recover ...
waiting ... 0
...
state changed: bus_off -> error_active
node recovered! continue

sending frame 0, please trigger error during sending

Troubleshooting

If the example doesn't enter the error_warning/error_passive/bus_off states after manual error triggering:

1. Check Hardware Connections: Ensure the TWAI transceiver is properly connected and powered.
2. Verify Bus Termination: Make sure the TWAI bus has proper 120Ω termination resistors at both ends.
3. Timing of Error Injection: The manual error should be triggered while frames are actively being transmitted.
4. Transceiver Type: Different TWAI transceivers may have different fault detection sensitivities.

If errors are not being detected:

• Try holding the disconnection/short-circuit for a slightly longer duration
• Ensure the error is introduced during active frame transmission
• Check that the TWAI H and TWAI L lines are properly connected to the transceiver