SLCAN Terminal

An interactive terminal application for sending and receiving raw SLCAN commands over a serial port. This is a C++ version based on slcan_attach.c that provides a direct command-line interface instead of creating a CAN network interface.

I created this to work with CANable 2.0 adapters with new firmware found here: https://github.com/Elmue/CANable-2.5-firmware-Slcan-and-Candlelight

Features

• Interactive terminal interface for SLCAN communication
• Automatic device detection (searches /dev/serial/by-id/ for devices with "slcan" in the name)
• Initialization commands for automatic device configuration
• Real-time display of received data
• Separate transmit (TX) and receive (RX) indicators
• Automatic feedback code interpretation - displays human-readable descriptions for SLCAN feedback codes (#, #1-#9, #:, #;, #<)
• Error code interpretation - automatically decodes detailed error reports (Exxxxxxxx format) with bus status, protocol errors, and error counts
• cansend-like syntax - use <can_id>#<data> format, automatically converted to SLCAN (like can-utils cansend)
• Support for all standard SLCAN commands
• Line editing with backspace support
• Graceful exit with 'quit', 'exit', or Ctrl+C

Building

Requirements

• CMake 3.10 or higher
• C++11 compatible compiler (g++, clang++)
• pthread library

Build Instructions

mkdir build
cd build
cmake ..
make

For a release build with optimizations:

mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Release ..
make

Installation

sudo make install

This will install the binary to /usr/local/bin/slcan_terminal.

Usage

./slcan_terminal [options] [tty_device]

Options

• -h, --help - Show help message
• -i, --init <commands> - Send initialization commands (comma-separated)

Note: If no tty_device is specified, the tool will automatically search for the first device in /dev containing "slcan" in its name.

Examples

Auto-detect SLCAN device:

./slcan_terminal

Auto-detect with initialization commands:

./slcan_terminal -i "C,S6,O"

Specify device explicitly:

./slcan_terminal /dev/ttyUSB0

With initialization commands (close, set speed to 500k, open):

./slcan_terminal -i "C,S6,O" /dev/ttyUSB0

With version check and configuration:

./slcan_terminal --init "C,V,S6,ON" /dev/ttyS1

Terminal Commands

Once in the terminal, you can enter SLCAN commands directly. Common commands include:

Configuration Commands

• V - Get version and serial number
• S0 to S8 - Set CAN speed:
  • S0 = 10 Kbit/s
  • S1 = 20 Kbit/s
  • S2 = 50 Kbit/s
  • S3 = 100 Kbit/s
  • S4 = 125 Kbit/s
  • S5 = 250 Kbit/s
  • S6 = 500 Kbit/s
  • S7 = 800 Kbit/s
  • S8 = 1000 Kbit/s

Channel Control

• O - Open channel (normal mode)
• ON - Open channel (normal mode, SLCAN 2.5)
• OS - Open channel (silent mode)
• L - Open channel (listen-only mode)
• C - Close channel
• F - Read status flags

CAN Frame Transmission

• tiiildd... - Transmit standard CAN frame

  • iii = 3-digit hex CAN ID
  • l = data length (0-8)
  • dd = data bytes in hex

  Example: t12348AABBCCDDEE1122 (ID=0x123, 8 bytes of data)

• Tiiiiiiiildd... - Transmit extended CAN frame

  • iiiiiiii = 8-digit hex CAN ID
  • l = data length (0-8)
  • dd = data bytes in hex

• riiil - Transmit standard RTR frame

• Riiiiiiiil - Transmit extended RTR frame

Simplified CAN Frame Format

The terminal supports a simpler format with automatic DLC calculation:

Format: <packet_type><can_id>#<data>

Packet Types:

• t - Standard (11-bit) CAN frame
• T - Extended (29-bit) CAN frame
• r - Standard RTR frame
• R - Extended RTR frame
• d - Standard CAN FD frame (FDF, no BRS)
• D - Extended CAN FD frame (FDF, no BRS)
• b - Standard CAN FD frame (FDF + BRS)
• B - Extended CAN FD frame (FDF + BRS)

Features:

• Data can be hex bytes optionally separated by dots (.) or spaces
• DLC is automatically calculated from data length
• Standard IDs are zero-padded to 3 hex digits
• Extended IDs are zero-padded to 8 hex digits

Examples:

# Standard CAN frame
> t123#DEADBEEF
[TX] t12304DEADBEEF

# With dots separating bytes
> t7E0#11.22.33.44
[TX] t7E00411223344

# Extended CAN frame
> T18AABBCC#112233
[TX] T18AABBCC03112233

# RTR frame (no data)
> r123#
[TX] r1230

# CAN FD with BRS (12 bytes)
> b123#112233445566778899AABBCC
[TX] b1239112233445566778899AABBCC

SLCAN Feedback Codes

When feedback mode is enabled (with MF command), the adapter sends feedback codes to indicate command status. The terminal automatically interprets these codes:

Code	Description
#	Success - command executed successfully
#1	Invalid command
#2	Invalid parameter
#3	Adapter must be open
#4	Adapter must be closed
#5	HAL error from ST Microelectronics
#6	Feature not supported/implemented
#7	CAN Tx buffer full (no ACK, 67 packets waiting)
#8	CAN bus off (severe error occurred)
#9	Sending not possible in silent mode
#:	Baudrate not set
#;	Flash Option Bytes programming failed
#<	Hardware reset required - reconnect USB

Example with feedback enabled:

> MF
[RX] # (Success)
> O
[RX] # (Success)
> InvalidCmd
[RX] #1 (Invalid command)

Error Code Interpretation

The terminal automatically decodes detailed error reports sent by the adapter in response to the F (status flags) command or error conditions. Error reports use the format Exxxxxxxx (E + 8 hex digits):

Format: Exxxxxxxx

Position	Description	Values
Digit 1	Bus Status	0=Active, 1=Warning Level, 2=Passive, 3=Bus Off
Digit 2	Last Protocol Error	0=None, 1=Bit stuffing, 2=Frame format, 3=No ACK, 4=Recessive bit, 5=Dominant bit, 6=CRC
Digits 3-4	Firmware Error Flags (hex)	0x01=Rx Failed, 0x02=Tx Failed, 0x04=CAN Tx overflow, 0x08=USB IN overflow, 0x10=Tx Timeout
Digits 5-6	Tx Error Count (hex)	0x00-0xFF
Digits 7-8	Rx Error Count (hex)	0x00-0xFF

Example error report:

> F
[RX] E03000505 (Bus Active, No ACK received, Tx Errors: 5, Rx Errors: 5)

Example Session

Basic session without initialization:

./slcan_terminal -i C,MF,MD,ME,MS,s\"1,239,80,80\",y\"4,10,9,9\",V,ON /dev/ttyACM0
command string: C,MF,MD,ME,MS,s"1,239,80,80",y"4,10,9,9",V,ON

=== Sending initialization commands ===
[INIT] C
[INIT] MF
[RESP] #
[INIT] MD
[RESP] #
[INIT] ME
[RESP] #
[INIT] MS
[RESP] #
[INIT] s1,239,80,80
[RESP] #
[INIT] y4,10,9,9
[RESP] #
[INIT] V
[RESP] +Board: MksMakerbase	MCU: STM32G431	DevID: 1128	Firmware: 2428963	Slcan: 100	Clock: 160	Limits: 512,256,128,128,32,32,16,16
[INIT] ON
[RESP] #
[RESP] >Nominal: 500k baud, 75.0%; Data: 2M baud, 55.0%; Perfect match: No
=== Initialization complete ===


=== SLCAN Terminal ===
Connected to: /dev/ttyACM0
Commands: Enter SLCAN commands (e.g., 'V' for version, 'O' to open)
Special: 'quit' or 'exit' to close, Ctrl+C to abort
======================

[RX] b01223456
[RX] b023A8877665544332211AABBCCDDEEFF0000
> C  
[TX] C
> quit

Terminal closed.

Differences from slcan_attach.c

The original slcan_attach.c creates a network CAN interface using the Linux SLCAN line discipline. This C++ version instead:

• Provides an interactive terminal interface
• Allows manual entry of SLCAN commands
• Displays both transmitted and received data in real-time
• Does not create a network interface
• Useful for debugging, testing, and direct SLCAN device interaction

License

Based on slcan_attach.c:

• SPDX-License-Identifier: (GPL-2.0-only OR BSD-3-Clause)