USB2CAN

Serializer to read and send frames from can bus using an usb connection.

Table of Content:

• General info
• Features
• Setup the can interface on Linux
• Can mask configuration on STM32
• Slcand encapsulation format
• Send can frames
• Dump can frames

General info

Board: Nucleo F446RE

For this project, the can is set in loopback mode in order to conduct tests more easily.
For a "real" test it is possible to connect two boards and set the can interface in normal mode.

Important notes

Baud Rate : 500.000 bits/s

Loopback mode : set PA11 to Pull-up

Normal mode : set PA11 to No pull-up and no pull-down

Features

Here a list of implemented features:

• Sniffing of standard can frames
• Sending of standarddata frames
• Sending of standard remote frames
• Dumping on terminal sniffed frames

An important note is that the board act as a "passive" component, in case it receives a remote frame, the board will not generate any frame as response. Moreover, extended frames are not managed and will not be sniffed nor sended.

Setup the can interface on Linux

In order to send can frames, we need first to setup the interface by using slcand, a module of the can-utils utility of Linux.
After that, we can use cansend and candump to send and receive frames.
Slcand allows us to generate a frame, send it through the UART connection. Before forwarding it to the "real" can bus, the board must create a can frame using the string generated by the slcand module.

It is possible to use the following scripts to manage more easily the setup of the interface and its detaching, both inside the folder Scripts.

./open.sh /dev/ttyACMX canX

./close.sh canX

If you need to change the baudrate, modify open.sh file (CAN bitrate reference).

Can mask configuration on STM32

It is possible not only to set a mask directly on the terminal of the host pc but also on the board to accept or reject the frames it receives.
The file can.c contains the function MX_CAN1_Init in which it is possible to define our mask.
The mask is set to 'anything' so, every frame the board receives will be taken and forwarded to the UART.

Slcand encapsulation format

Slcand uses a specific encapsulation format to send and receive the can frames, more details can be found here from line 133.

Briefly, we have:

• Type : t, r, T, R
• Id : 3 (standard) or 8 (extended) bytes in ASCII Hex (base64)
• Dlc : one byte ASCII number ('0' - '8')
• Data : section has at much ASCII Hex bytes as defined by the dlc

At the moment, the project manages only the standard frames both for tranismit and receiving.

Send can frames

Simply run the following commands:

cansend can0 123#DEADBEEF
cansend can0 123#R4

where as example we send with ID = 123 the payload DEADBEEF and send a remote request for 4 bytes.

cangen can0

If we want to generate a series of random frames, cangen is the solution.

Dump can frames

Simply run the following command:

candump can0

All traffic will be intercepted (based on the mask of the board / terminal) and will be displayed on terminal.

candump can0 -l

If you want to log all frames into an auto-generated file.

Authors

Dorijan Di Zepp dorijan.dizepp@eagletrt.it