S15: Protocol Interface: I2C - CAN Bridge

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Serial Protocol Convertor

Abstract

This project is aimed at developing a device, which is able to convert the incoming data from one protocol to another (I2C, UART, SPI, CAN). In a system operating over a CAN architecture, there is a need of an inbuilt CAN peripheral interface in every controller. Because of hardware limitations, many controllers do not support the CAN peripherals; therefore they are restricted to communicate over the limited number of protocols. This device provides a flexibility to the designers so that they can choose any communication protocol at the input, and convert the data to the desired protocol.

Objectives & Introduction

Basically, this device will convert the incoming data from one protocol to the other desired protocol. Considering the problems faced in an industry, the main goal of this project is to enable the designers to use a controller, that supports any serial protocol, to the system using CAN bus. For designing a protocol converter, there are some aspects such as speed synchronization and bi-directional communication, which are necessary to make this device useful. A practical example would be connecting an I2C device to the CAN system. Since the I2C protocol consists of a master - slave approach, it is not possible to control the I2C master by I2C slave. In this project, these conditions are handled using hardware interrupts. Also speed synchronization is a crucial aspect, as every protocol supports different data speed. The concept of Queues and Mailboxes is used to handle the speed limitations. FreeRTOS is used for designing the software of this system.

Team Members & Responsibilities

S.R. Team Member's Name Tasks
1 Ishan Bhavsar
  • Hardware Design
  • Report and Datasheet
  • Designing of Memory Map, Registers and Addressing Scheme
2 Tej Kogekar
3 Rutwik Kulkarni
  • Software Design for Protocol Interface
  • Software Design for I2C Master and CAN Devices on the bus (For Testing and Demonstration)
4 Mitesh Sanghvi

Schedule

Team Schedule
S.R. Start Date End Date Task Status Actual Completion
Date
1 03/08/2015 03/14/2015 Develop driver for interrupt based I2C acting as a Slave Device Completed 03/14/2015
2 03/15/2015 03/21/2015 Exploring CAN API and building CAN bus for communication Completed 03/21/2015
3 03/22/2015 03/28/2015 Study and Design mailbox system for CAN messages Completed 03/28/2015
4 03/29/2015 04/04/2015 Develop program for configuring the Protocol Interface by I2C Master Completed 04/04/2015
5 04/05/2015 04/11/2015 Create task for storing CAN messages in mailboxes Completed 04/11/2015
6 04/12/2015 04/18/2015 Create task for giving interrupt to I2C Master Completed 04/18/2015
7 04/19/2015 04/25/2015 Create task for sending message on CAN recieved from I2C Master Completed 04/25/2015
8 04/26/2015 05/02/2015 Design of Status Register for Protocol Interface Completed 05/02/2015
9 05/03/2015 05/09/2015 Finalizing appropriate addresses for all registers Completed 05/09/2015
10 05/10/2015 05/16/2015 Testing of Protocol Interface for various conditions Completed 05/12/2015
11 05/17/2015 05/23/2015 Adding a feature of Bit-Masked CAN IDs Completed 05/22/2015

Parts List & Cost

S.R. Description Manufacturer Part Number Qty Cost
1 SJOne Board - - 1 $80.00
2 Ultrasonic Sensor (Optional) Parallax 28015 1 $23.00
3 CAN Transceiver (Free Samples) Microchip MCP2551 1 $0.00
4 Linear Voltage Regulator (Free Sample) LT LT1083-5 1 $0.00
Total $103.00

Design & Implementation

The design section can go over your hardware and software design. Organize this section using sub-sections that go over your design and implementation.

Hardware Design

This project is used as an interface for an I2C controller to communicate over the CAN bus. The I2C controller should act as an I2C master and the Protocol Interface device will act as an I2C slave device. Since the communication from the I2C slave to the I2C master is not possible, external GPIO interrupts are used. The Protocol Interface has an inbuilt CAN peripheral to communicate over the CAN bus. The I2C master is supposed to configure the mailboxes of the interface for the particular CAN ID’s. These mailboxes are used to store the CAN messages received by the Protocol Interface over the CAN bus. Whenever a message is received by the CAN peripheral, it is stored in the respective mailbox. Once the number of Data Frames stored in any mailbox reached the limit (configured by I2C Master), an interrupt is given. The Protocol Interface uses SJOne development board for the communication that supports both I2C and CAN protocols. The write and read address of the Protocol Interface is 0x50 and 0x51 respectively, which are used by the I2C master for the communication.


Figure 1. Block Diagram

Hardware Interface

In this section, you can describe how your hardware communicates, such as which BUSes used. You can discuss your driver implementation here, such that the Software Design section is isolated to talk about high level workings rather than inner working of your project.

Software Design

Configure Mailbox

  1. Start
  2. Receive data over I2C bus from I2C Master
  3. Check if the first data byte i.e. mailbox number lies between 0 and 15
  4. If mailbox number is invalid, then give out an error
  5. Receive next two data bytes which contains the CAN_id and the size of the particular mailbox
  6. Check for the Mask Bit in the data
  7. If mask is one, then receive two more data bytes from I2C Master and store them as Mask_id for that mailbox
  8. Go to Step 2


CAN to Mailbox

  1. Start
  2. Wait for data to be received over CAN bus using CAN_rx() with a timeout of PortMAXDELAY
  3. Check whether received CAN_id is amongst the configured CAN_id for any mailbox
  4. If CAN_id belongs to any mailbox, then check for number of Data Frames already present in that particular mailbox
  5. If CAN_id does not belong to any mailbox, discard the message
  6. If Data Frames present in any mailbox exceeds the configured size of that mailbox, give an external interrupt to I2C Master through GPIO and also set the corresponding bit in the Status Register
  7. Go to Step 2
Figure 2. Flowchart on Configuring Mailbox
Figure 3. Flowchart on Receiving Data from CAN bus and Storing into Mailboxes

Read Status Register

  1. Start
  2. Receive data over I2C bus from I2C Master
  3. Check if the data byte received is 0xFE which is the memory address of Status Register
  4. If yes, then send the two data bytes of Status Register to I2C Master
  5. Go to Step 2


Read Mailbox Data

  1. Start
  2. Receive data over I2C bus from I2C Master and set it as Requested Mailbox
  3. In a new Read Transaction initiated by I2C Master, send the Data Frames of requested Mailbox Number
  4. Clear the corresponding bit in Status Register
  5. Go to Step 2
Figure 4. Flowchart on Reading Status Register
Figure 5. Flowchart on Reading Mailbox Data

Send Data over CAN

  1. Start
  2. Receive data over I2C bus from I2C Master
  3. Check if the data byte received is 0xFF which is the memory address of CAN Transmit Register
  4. If yes, then receive 10 data bytes from I2C Master
  5. Set first two bytes are CAN_id and remaining eight bytes as CAN data bytes
  6. Send the CAN frame over CAN bus
  7. Go to Step 2
Figure 6. Flowchart on Sending Data over CAN Bus

Implementation

The steps involved in implementation of this project are as follows:

  • During boot-up process of Protocol Interface, I2C and CAN drivers are initialized.
  • The device is ready to accept messages from I2C Master to be sent over the CAN bus. The data frame is as follows:
Figure 1. Data Frame sent by I2C Master to Protocol Interface for sending data over CAN Bus
  • The I2C Master write data to Configuration Registers of respective Mailbox. The data frame is as follows:
Figure 1. Data Frame sent by I2C Master to configure mailboxes of Protocol Interface
  • According to the Configuration Registers, the mailboxes are configured for specific CAN_id, size and optional Mask_id.
  • The device will continuously keep on accepting messages from CAN bus. For every message received, the software will check whether the received CAN_id matches with the configured mailbox CAN_id. If the id matches, then the Data Frame i.e. CAN_id and 8-bytes of Data is stored in the particular mailbox.
  • For all the received messages, if a particular mailbox is configured with Mask_id, then it will also check the received CAN_id to match with the masked CAN_id.
  • Once the message is saved in the mailbox, it will check whether the number of frames stored in a mailbox exceeds the configured size for that mailbox. If it exceeds, then device will give an external GPIO interrupt to I2C Master.
  • On receiving an interrupt, I2C Master will initiate read transaction to read the Status Register. The data frame is as follows:
Figure 1. Data Frame for sending Status Register from Protocol Interface to I2C Master
  • Looking at the bits set in the Status Register, I2C Master will decide to read the data from any one mailbox at a time.
  • I2C Master will initiate read transaction for one mailbox and device will send the data frames of requested mailbox. The data frame is as follows:
Figure 1. Data Frame for sending CAN data stored in mailboxes to I2C Master

Testing & Technical Challenges

Describe the challenges of your project. What advise would you give yourself or someone else if your project can be started from scratch again? Make a smooth transition to testing section and described what it took to test your project.

Include sub-sections that list out a problem and solution, such as:

My Issue #1

Discuss the issue and resolution.

Conclusion

Conclude your project here. You can recap your testing and problems. You should address the "so what" part here to indicate what you ultimately learnt from this project. How has this project increased your knowledge?

Project Video

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Project Source Code

References

Acknowledgement

Any acknowledgement that you may wish to provide can be included here.

References Used

  1. LPC_USER_MANUAL
  2. Ultrasonic Sensor
  3. GLCD with Touchscreen
  4. CAN Transceiver
  5. Linear Voltage Regulator
  6. Socialledge Embedded Systems Wiki
  7. Preetpal Kang, Lecture notes of CMPE 243, Computer Engineering, Charles W. Davidson College of Engineering, San Jose State University, Aug-Dec 2014.
  8. en.wikipedia.org/
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