This memo provides information about how to read real time CAN data through the OOBD firmware. Distribution of this memo is unlimited.

Copyright (C) OOBD Team (2012). All Rights Reserved.

To surround several constrains like bus speed, real time capabilities and memory size when recording real time data in OOBD, the following concept will be followed

1. To avoid the use of proprietary intellectual property, the data fields to be recorded are not hardcoded in the firmware, they will be instead configured by the application at start-up
2. To avoid unpredictable bus speed bottlenecks, the data will only be collected in the firmware and only transferred on request.
3. To reuse existing code on application side, the configuration and the data request will be implemented as pseudo UDS services: Service 27 (Write Data) to configure, Service 22 (Read Data) to read.

Select the CAN RTD protocol

p 1 1 3 0

Open the CAN filters

p 8 10 1 0
p 8 11 1 0

This activates the CAN Real Time Protocol, clears the internal PID list and sets the CAN bus into “invisible listen” mode

The data to listen to is defined by the application to the firmware with an 27- command:

27 CanID Type [Length [cPos [cStart]]]

Values not given use 0 as default value

where the data byte meanings are as follows:

Request Single frame with ID 0400

27 00000400

Request Single frame (=type 00) with ID 0400 and length 3

27 00000400 00 0003

Request custom multi frame (=type 01) with ID 400 , length 20, sequence counter position at Byte 3 and starting value of 2

27 00000400 01 0014 03 02

Request ISO-TP multiframe (=type 02) with ID 400 (length is taken dynamically out of first frame info)

27 00000400 02

The request to the firmware to send received data to the application is done with an 22- command:

22 AA BB CC DD

where the data byte meanings are as follows:

As result the firmware first repeats the command + 40H (=0x62) , a four byte timestamp (AABBCCDD, FreeRTOS ticks), a one byte flag (FL) and the received data bytes after that:

62 AA BB CC DD FL 00 11 22 ..

In the moment only bit 0 of the flag is used. If set, the data output is new and has not been printed before. After printed, the flag is set to 0 by the firmware. So when bit 0 is set, this is fresh data. By that the application software don't need to control by itself (by the time stamps) if this data has already been received before or if its new data.

the error messages are designed as General Response Code Errors, means they are coded as received bytes, not as clear text error messages. The byte sequence always starts with 7F 00, followed by the error code byte:

1. All requested CAN-IDs are internally handled as list of elements
2. In case a requested CAN ID is > 8 bytes, then the element needs to have two receive buffers (double buffering), to make make sure that there's always one buffer ready to read, while the other one is just in the fill process by the CAN interrupt handler.
3. The implementation needs to make sure, that a buffer is not altered during its printout process
4. The implementation needs to make sure, that a buffer is only declared as valid, if a complete frame sequence (0..x) has been received without disturbance.

This RFC raises security issues. It's need to make sure that the firmware only listens on the bus in invisible mode without creating any active (re)action on the bus.

Steffen Koehler

Phone: +49 172 410 35 98

EMail:steffen@koehlers.de

Copyright (C) OOBD Team (2012). All Rights Reserved.

This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the OOBD Team organizations, except as needed for the purpose of developing standards in which case the procedures for copyrights defined in the Standards process must be followed, or as required to translate it into languages other than English.

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