esp-idf/examples/peripherals/twai/twai_utils

Supported Targets	ESP32	ESP32-C3	ESP32-C5	ESP32-C6	ESP32-H2	ESP32-H21	ESP32-H4	ESP32-P4	ESP32-S2	ESP32-S3	ESP32-S31

TWAI Console Example

This example demonstrates using the TWAI (Two-Wire Automotive Interface) driver through an interactive console interface. It provides comprehensive TWAI functionality including frame transmission/reception, message filtering, and bus monitoring. The example can be used for both standalone testing via loopback mode and real TWAI network communication.

Supported Commands:

Command	Description	Linux can-utils Equivalent
twai_init <controller> -t <tx> -r <rx> [opts]	Initialize TWAI controller with GPIO and mode options	ip link set can0 up type can bitrate 500000
twai_deinit <controller>	Deinitialize TWAI controller	ip link set can0 down
twai_send <controller> <frame>	Send TWAI frame (standard/extended/RTR/FD)	cansend can0 123#DEADBEEF
twai_dump <controller>[,filter] [-t mode] / twai_dump <controller> --stop	Monitor TWAI traffic with hardware filtering and timestamps	candump can0
twai_info <controller>	Display controller configuration, status	ip -details link show can0
twai_recover <controller> [-t <ms>]	Recover controller from Bus-Off state	N/A

• Note: twai_dump runs continuously in the background. Use twai_dump <controller> --stop to stop monitoring.

How to Use This Example

Hardware Required

• Any ESP development board with TWAI support.
• A TWAI transceiver (e.g., SN65HVD230, TJA1050).
• Jumper wires.

Hardware Setup

Connect the ESP board to a transceiver:

ESP32 Pin     Transceiver    TWAI Bus
---------     -----------    --------
GPIO4 (TX) -->  CTX
GPIO5 (RX) <--  CRX
3.3V/5V    -->  VCC
GND        -->  GND
              TWAI_H     <-->  TWAI_H
              TWAI_L     <-->  TWAI_L

Note: The specific GPIO pins for TX and RX must be provided in the twai_init command.

Quick Start - No Transceiver Mode

For immediate testing without any external hardware, you can use the No Transceiver Mode by connecting a single GPIO pin to itself.

# Connect GPIO4 to itself (or leave it unconnected for self-test)
# Initialize with the same TX/RX GPIO, and enable loopback and self-test modes.
twai> twai_init twai0 -t 4 -r 4 --loopback --self-test

# Send a test frame
twai> twai_send twai0 123#DEADBEEF

# Check controller status
twai> twai_info twai0

This mode is ideal for learning the commands, testing application logic, and debugging frame formats without a physical bus.

Configure the project

idf.py menuconfig

Navigate to Example Configuration -> TWAI Configuration and configure:

• Default Arbitration Bitrate: Default arbitration bitrate in bits per second (bps).
• Default FD Data Bitrate: Default data bitrate for TWAI-FD in bits per second (bps).
• Enable TWAI-FD Support: Enable TWAI-FD (Flexible Data-rate) support (default: disabled)
• TX Queue Length: Length of the transmission queue for TWAI messages (default: 10)

Note: For every controller, you must specify the TX and RX pins explicitly with the -t and -r options when issuing twai_init. Failing to do so will make initialization return an error.

Build and Flash

idf.py -p PORT flash monitor

(To exit the serial monitor, type Ctrl-].)

Command Reference

twai_init

Initializes and starts the TWAI driver. TX and RX pins are required.

Usage: twai_init <controller> -t <tx_gpio> -r <rx_gpio> [options]

Arguments:

• <controller>: Controller ID (twai0, twai1).
• -t, --tx: TX GPIO pin number (required).
• -r, --rx: RX GPIO pin number (required).
• -b, --bitrate: Arbitration bitrate in bps (default: CONFIG_EXAMPLE_DEFAULT_BITRATE).
• -B, --fd-bitrate: Data bitrate for TWAI-FD (FD-capable chips only, default: CONFIG_EXAMPLE_DEFAULT_FD_BITRATE).
• --loopback: Enable loopback mode.
• --self-test: Enable self-test mode (internal loopback).
• --listen: Enable listen-only mode.
• -c, --clk-out: Clock output GPIO pin (optional).
• -o, --bus-off: Bus-off indicator GPIO pin (optional).

twai_deinit

Stops and de-initializes the TWAI driver.

Usage: twai_deinit <controller>

twai_send

Sends a standard, extended, RTR, or TWAI-FD frame.

Usage: twai_send <controller> <frame_str>

Frame Formats:

• Standard: 123#DEADBEEF (11-bit ID)
• Extended: 12345678#CAFEBABE (29-bit ID)
• RTR: 456#R or 456#R8 (Remote Transmission Request)
• TWAI-FD: 123##{flags}{data} (FD-capable chips only)
  • flags: single hex nibble 0..F
    • bit0 (0x1) = BRS (Bit Rate Switch, accelerate data phase)
    • bit1 (0x2) = ESI (Error State Indicator)
    • other bits reserved (set to 0)
  • data: up to 64 bytes (0..64) of hex pairs, optional . separators allowed (e.g. 11.22.33)
  • example: 123##1DEADBEEF (BRS enabled, data = DE AD BE EF)

twai_dump

Monitors TWAI bus messages with filtering and candump-style output. This command runs in the background.

Usage:

• twai_dump [-t <mode>] <controller>[,filter...]

• twai_dump <controller> --stop

• Options:

• -t <mode>: Timestamp mode. Output format is (seconds.microseconds) with 6-digit microsecond precision, e.g. (1640995200.890123).

  • a: Absolute time (esp_timer microseconds since boot)
  • d: Delta time between frames (time since previous frame)
  • z: Zero-relative time from start (time since dump started)
  • n: No timestamp (default)

• --stop: Stop monitoring the specified controller.

Filter Formats:

• id:mask: Mask filter (e.g., 123:7FF).
• low-high: Range filter (e.g., 100-200, FD-capable chips only).
• Multiple filters can be combined with commas (e.g., twai0,123:7FF,100-200).

twai_info

Displays the TWAI controller's configuration and real-time status.

Usage: twai_info <controller>

Output Includes:

• Status (Stopped, Running, Bus-Off)
• Node State (Error Active, Error Passive, etc.)
• TX/RX Error Counters
• Bitrate (Arbitration and Data)
• Configured GPIOs and operational modes.

twai_recover

Initiates recovery for a controller that is in the Bus-Off state.

Usage: twai_recover <controller> [-t <ms>]

Options:

• -t <ms>: Recovery timeout.
  • -1: Block indefinitely until recovery completes (default).
  • 0: Asynchronous recovery (returns immediately).
  • >0: Timeout in milliseconds.

Notes:

• Recovery only works when the controller is in Bus-Off state
• Use twai_info <controller> to check current node state
• Recovery may fail if bus conditions are still problematic
• In async mode (timeout=0), use twai_info to monitor recovery progress

Typical Command Sequence:

1. twai_init - Initialize controller
2. twai_info - Check status
3. twai_dump - Start monitoring (optional)
4. twai_send - Send frames
5. twai_recover - Recover from errors (if needed)
6. twai_deinit - Cleanup

Basic usage example:

# Initialize controller 0 (bitrate 500 kbps, specify TX/RX pins)
twai> twai_init twai0 -b 500000 -t 4 -r 5

# Display controller information
twai> twai_info twai0
TWAI0 Status: Running
Node State: Error Active
Error Counters: TX=0, RX=0
Bitrate: 500000 bps
GPIOs: TX=GPIO4, RX=GPIO5

# Send standard frame on controller 0
twai> twai_send twai0 123#DEADBEEF

# Start monitoring controller 0 (accept all frames)
twai> twai_dump twai0

# Example received frame display (with default no timestamps)
  twai0  123  [4]  DE AD BE EF

FD-Capable Chips Example

# Initialize controller 0 with TWAI-FD enabled
twai> twai_init twai0 -b 1000000 -t 4 -r 5 -B 2000000

twai> twai_info twai0
TWAI0 Status: Running
Node State: Error Active
Error Counters: TX=0, RX=0
Bitrate: 1000000 bps (FD: 2000000 bps)
GPIOs: TX=GPIO4, RX=GPIO5

# Send FD frame with BRS on controller 0
twai> twai_send twai0 456##1DEADBEEFCAFEBABE1122334455667788

PC Environment Setup (For Full Testing)

To test bidirectional communication between ESP32 and PC, set up a SocketCAN environment on Ubuntu:

Prerequisites

• Ubuntu 18.04 or later
• USB-to-CAN adapter (PEAK PCAN-USB recommended)
• sudo access for network interface configuration

Quick Setup

1. Install CAN utilities:

sudo apt update
sudo apt install -y can-utils

# Verify installation
candump --help
cansend --help

2. Configure CAN interface:

# Classic CAN setup (500 kbps)
sudo ip link set can0 up type can bitrate 500000

# CAN-FD setup (1M arbitration, 4M data) - requires FD-capable adapter
sudo ip link set can0 up type can bitrate 1000000 dbitrate 4000000 fd on

# Verify interface
ip -details link show can0

3. Test PC setup:

# Terminal 1: Monitor
candump can0

# Terminal 2: Send test frame
cansend can0 123#DEADBEEF

# Send FD frame (if FD adapter available)
cansend can0 456##1DEADBEEFCAFEBABE

Bidirectional Testing

Once both PC and ESP32 are set up:

ESP32 to PC:

# PC: Start monitoring
candump can0

# ESP32: Initialize controller 0 and send frame
twai> twai_init twai0 -t 4 -r 5
twai> twai_send twai0 123#DEADBEEF

# PC shows: can0  123   [4]  DE AD BE EF
# ESP32 shows: twai0  123  [4]  DE AD BE EF

PC to ESP32:

# ESP32: Start monitoring controller 0
twai> twai_dump twai0

# PC: Send frame
cansend can0 456#CAFEBABE

# ESP32 shows:  twai0  456  [4]  CA FE BA BE

# Stop monitoring
twai> twai_dump twai0 --stop

Advanced Features

Frame Formats

• Standard frames: 123#DEADBEEF (11-bit ID)
• Extended frames: 12345678#CAFEBABE (29-bit ID)
• RTR frames: 456#R8 (Remote Transmission Request)
• TWAI-FD frames: 123##1DEADBEEF (FD with flags, FD-capable chips only)
• Data separators: 123#DE.AD.BE.EF (dots ignored)

TWAI-FD Frame Format and Examples (FD-capable chips only)

TWAI-FD frames use two # characters: ID##{flags}{data}.

• Flags are a single hex nibble (0..F). Bit meanings:
  • 0x1 BRS: Enable Bit Rate Switch for the data phase
  • 0x2 ESI: Error State Indicator
  • Other bits are reserved (set to 0)
• Data payload supports up to 64 bytes. The driver maps the payload length to the proper DLC per CAN FD rules automatically.
• Payload hex pairs may include . separators for readability (ignored by the parser).

# FD frame without BRS (flags = 0) on controller 0
twai> twai_send twai0 123##0DEADBEEFCAFEBABE1122334455667788

# FD frame with BRS (flags = 1, higher data speed)
twai> twai_send twai0 456##1DEADBEEFCAFEBABE1122334455667788

# FD frame with ESI (flags = 2)
twai> twai_send twai0 789##2DEADBEEF

# FD frame with BRS + ESI (flags = 3)
twai> twai_send twai0 ABC##3DEADBEEF

# Large FD frame (up to 64 bytes)
twai> twai_send twai0 DEF##1000102030405060708090A0B0C0D0E0F101112131415161718191A1B1C1D1E1F202122232425262728292A2B2C2D2E2F303132333435363738393A3B3C3D3E3F

Filtering and Monitoring

# Monitor controller 0 (accept all frames)
twai> twai_dump twai0
  twai0  123  [4]  DE AD BE EF
  twai0  456  [2]  CA FE
  twai0  789  [8]  11 22 33 44 55 66 77 88

# Monitor with absolute timestamps
twai> twai_dump -t a twai0
(1640995200.890123)   twai0  123  [4]  DE AD BE EF
(1640995200.895555)   twai0  456  [2]  CA FE
(1640995200.901000)   twai0  789  [8]  11 22 33 44 55 66 77 88

# Monitor with delta timestamps (time between frames)
twai> twai_dump -t d twai0
(0.000000)   twai0  123  [4]  DE AD BE EF
(0.005432)   twai0  456  [2]  CA FE
(0.005445)   twai0  789  [8]  11 22 33 44 55 66 77 88

# Monitor with zero-relative timestamps (from start of monitoring)
twai> twai_dump -t z twai0
(0.000000)   twai0  123  [4]  DE AD BE EF
(0.005432)   twai0  456  [2]  CA FE
(0.010877)   twai0  789  [8]  11 22 33 44 55 66 77 88

# Monitor without timestamps (default)
twai> twai_dump -t n twai0
  twai0  123  [4]  DE AD BE EF
  twai0  456  [2]  CA FE
  twai0  789  [8]  11 22 33 44 55 66 77 88

# Monitor controller 0 with exact ID filter (only receive ID=0x123)
twai> twai_dump twai0,123:7FF
  Mask Filter 0: ID=0x00000123, mask=0x000007FF, STD
   twai0  123  [4]  DE AD BE EF

# Monitor controller 0 with ID range 0x100-0x10F (mask filter approach)
twai> twai_dump twai0,100:7F0
  Mask Filter 0: ID=0x00000100, mask=0x000007F0, STD

# Monitor controller 0 with range filter (0xa to 0x15) - FD-capable chips only
twai> twai_dump twai0,a-15
  Range Filter 0: 0x0000000a - 0x00000015, STD

# Monitor controller 0 with range filter (0x000 to 0x666)
twai> twai_dump twai0,000-666
  Range Filter 0: 0x00000000 - 0x00000666, STD

# Monitor controller 0 with mixed filters (mask + range)
twai> twai_dump twai0,123:7FF,a-15
  Mask Filter 0: ID=0x00000123, mask=0x000007FF, STD
  Range Filter 0: 0x0000000a - 0x00000015, STD

# Monitor controller 0 with dual filters
twai> twai_dump twai0,020:7F0,013:7F8
  Mask Filter 0: ID=0x00000020, mask=0x000007F0, STD
  Mask Filter 1: ID=0x00000013, mask=0x000007F8, STD

# Monitor controller 0 with multiple range filters  
twai> twai_dump twai0,10-20,100-200
  Range Filter 0: 0x00000010 - 0x00000020, STD
  Range Filter 1: 0x00000100 - 0x00000200, STD

# Monitor all frames on controller 0 (no filter)
twai> twai_dump twai0

# Stop monitoring controller 0
twai> twai_dump twai0 --stop

Filter Types (FD-capable chips only):

• Mask filters: id:mask format - Uses bitwise matching with configurable mask
• Range filters: low-high format - Hardware range filtering for ID ranges
• Mixed filtering: Combine both types in one command for maximum flexibility

Testing Modes

No Transceiver Mode (Testing without external hardware):

# Use same GPIO for TX and RX with loopback and self-test
twai> twai_init twai0 -t 4 -r 4 --loopback --self-test
twai> twai_dump twai0
twai> twai_send twai0 123#DEADBEEF
# Frame appears immediately in dump output:
  twai0  123  [4]  DE AD BE EF
twai> twai_dump twai0 --stop

Note: This mode is perfect for testing TWAI functionality without external transceivers or wiring. The same GPIO is used for both TX and RX, and the combination of --loopback and --self-test flags ensures frames are properly transmitted and received internally.

Loopback mode (with external transceiver):

twai> twai_init twai0 -t 4 -r 5 --loopback
twai> twai_dump twai0
twai> twai_send twai0 123#54455354
# Frame appears immediately in dump output:
  twai0  123  [4]  54 45 53 54

# Stop monitoring when done
twai> twai_dump twai0 --stop

# FD loopback test (FD-capable chips only)
twai> twai_init twai0 -t 4 -r 5 --loopback -B 2000000
twai> twai_dump twai0
twai> twai_send twai0 456##1DEADBEEFCAFEBABE1122334455667788
  twai0  456  [16]  DE AD BE EF CA FE BA BE 11 22 33 44 55 66 77 88  # FD frame (BRS)

# Stop monitoring
twai> twai_dump twai0 --stop

Listen-only mode:

twai> twai_init twai0 -t 4 -r 5 --listen
twai> twai_dump twai0
# Can receive but cannot send frames
# Stop with: twai_dump twai0 --stop

Error Recovery and Diagnostics

Bus-Off Recovery: The TWAI controller can enter a Bus-Off state due to excessive error conditions. Use the twai_recover command to initiate recovery:

# Basic recovery (default: block until complete)
twai> twai_recover twai0
I (1234) cmd_twai_core: Starting recovery from Bus-Off state...
I (1345) cmd_twai_core: Waiting for recovery to complete...
I (1456) cmd_twai_core: Recovery completed successfully in 100 ms

# Recovery with custom timeout
twai> twai_recover twai0 -t 5000
I (1234) cmd_twai_core: Starting recovery from Bus-Off state...
I (1345) cmd_twai_core: Waiting for recovery to complete...
I (1456) cmd_twai_core: Recovery completed successfully in 150 ms

# Asynchronous recovery (return immediately)
twai> twai_recover twai0 -t 0
I (1234) cmd_twai_core: Starting recovery from Bus-Off state...
I (1245) cmd_twai_core: Recovery initiated (async mode)

# If node is not in Bus-Off state
twai> twai_recover twai0
I (1234) cmd_twai_core: Recovery not needed - node is Error Active

Enhanced Status Information: The twai_info command now displays real-time dynamic status information:

twai> twai_info twai0
TWAI0 Status: Running
Node State: Error Active
Error Counters: TX=0, RX=0
Bitrate: 500000 bps
GPIOs: TX=GPIO4, RX=GPIO5

Status and Node State Interpretations:

• Status: Running: Driver initialized and operational (not Bus-Off)
• Status: Bus-Off: Controller offline due to excessive errors, requires recovery
• Status: Stopped: Driver not initialized
• Node State: Error Active: Normal operation, can transmit and receive freely
• Node State: Error Warning: Warning level reached (error counters ≥ 96)
• Node State: Error Passive: Passive mode (error counters ≥ 128, limited transmission)
• Node State: Bus Off: Controller offline (TX error counter ≥ 256, requires recovery)

Troubleshooting

Restoring Default Configuration: Use twai_deinit <controller> followed by twai_init <controller> to reset the driver to default settings.

Bus-Off Recovery Issues:

• "Node is not in Bus-Off state": Recovery only works when the controller is in Bus-Off state. Use twai_info to check current node state.
• Recovery timeout: If recovery takes longer than expected, try increasing the timeout with -t option (e.g., -t 15000 for 15 seconds).
• Recovery fails: Check physical bus conditions, ensure proper termination and that other nodes are present to acknowledge recovery frames.

TWAI-FD specific issues:

• "TWAI-FD frames not supported": Your chip doesn't support FD mode. Use chips like ESP32-C5
• FD bitrate validation: Ensure FD data bitrate is higher than arbitration bitrate
• PC FD compatibility: Ensure your PC CAN adapter supports FD mode

PC CAN issues:

# Reset PC interface
sudo ip link set can0 down
sudo ip link set can0 up type can bitrate 500000

# For FD mode
sudo ip link set can0 up type can bitrate 1000000 dbitrate 4000000 fd on

No communication:

• Verify bitrates match on both sides
• For FD: Ensure both sides support FD and have compatible transceivers
• Check physical connections and transceiver power
• GPIO pins must be specified in the twai_init command (common: TX=GPIO4, RX=GPIO5)
• For no-transceiver testing, use the same GPIO for both TX and RX with --loopback --self-test flags
• Ensure proper CAN bus termination (120Ω resistors)
• Use loopback mode to test ESP32 functionality independently

Quick diagnostic with no-transceiver mode:

# Test if basic TWAI functionality works
twai> twai_init twai0 -t 4 -r 4 --loopback --self-test
twai> twai_send twai0 123#DEADBEEF
# If this fails, check ESP-IDF installation and chip support

Common Error Messages:

# Controller ID missing
twai> twai_send 123#DEADBEEF
E (1234) cmd_twai_send: Controller ID is required

# Interface not initialized
twai> twai_send twai0 123#DEADBEEF
E (1234) cmd_twai_send: TWAI0 not initialized

# Invalid frame format
twai> twai_send twai0 123DEADBEEF
E (1456) cmd_twai_send: Frame string is required (format: 123#AABBCC or 12345678#AABBCC)

# Invalid controller ID
twai> twai_init twai5 -t 4 -r 5
E (1678) cmd_twai_core: Invalid controller ID