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Cnfiguration of the Flexray GTU (Global Time Unit)

Pradeepa Senanayake
Intellectual 715 points
Other Parts Discussed in Thread: TMS570LS1115

Hello,

I have been checking the Flexray module of TMS570LS1115 Safety Hercules micro-controller. I am using this for a rail application. I am currently setting up the Flexray communication for my devices.

I have been checking the examples given by TI. I would like to clarify few things in those examples related to GTU configuration.

  • How to select the length of the Macrotick? What are the things to configure?(In the example you have selected 1MT = 40uT)

In those examples the Flexray baudrate is set to 10Mbps. So it takes 100ns to transmit a single bit. Since the uT time is 25ns, we need 4uT to transfer one bit. During a Macrotick there will be 10bits transferred(1MT = 40uT). Since the length of a static slot is configured as 86, the number of bits in a static slot is 860.

  • Is the above calculation correct?
  • This means that to transfer a single message buffer in the RAM. It takes multiple communication cycles. Since 860 is not byte/word aligned will this cause any issue? Or is the Flexray controller properly handling this internally?
  • What is the meaning of the initial offset?
  • What is the action point and what are the things to consider when configuring it?

Thank you.

  • 0
    TI__Guru 68920 points
    Please see if there are answers www.ti.com/.../getliterature.tsp
    I don't know much about FlexRay myself. It's not used very commonly.
  • 0 in reply to Anthony F. Seely
    Intellectual 715 points

    Thank you for the help.

    I have referred to that training material. It is a subset of what is available in the Reference Manual.

    The only other thing I have to read is the Flexray specification itself. Which is available here,

    https://svn.ipd.kit.edu/nlrp/public/FlexRay/

    In the meantime, if there is anyone who can answer the above questions please give me some insight. 

    There should be Flexray experts. Or is Flexray outdated or something?

  • 0 in reply to Pradeepa Senanayake
    TI__Guru 68920 points
    "There should be Flexray experts. Or is Flexray outdated or something?"
    You may be onto something. When I googled FlexRay and sorted by time - there wasn't very much that came up this year and the training was at the top of the list. You could look at www.bosch-semiconductors.de/.../in_vehicle_communication_3.html
    But for what it's worth - unless you are required to use FlexRay for an automotive project - you might think twice or three times or four times or even five times about it and consider Ethernet instead.
  • 0 in reply to Anthony F. Seely
    Intellectual 715 points

    Hello,

    Anthony F. Seely said:
    But for what it's worth - unless you are required to use FlexRay for an automotive project - you might think twice or three times or four times or even five times about it and consider Ethernet instead.

    Is there any specific reason for this statement? Or is it because of the simplicity?

    Usually apart from CAN what is the most used communication protocol in Automobiles? Is it Flexray or Byteflight?

    Thank you for the links. So it seems like the E-Ray block is an IP developed by Bosch and then integrated to TI chips?

  • 0 in reply to Pradeepa Senanayake
    TI__Guru 68920 points

    Hi Pradeepa,

    Just my opinion (personal).  You should do some research.   Maybe ask about Ethernet v.s. FlexRay long term on our Ethernet forum

    or read some articles like:

    It's hard to argue with the success of IEEE ethernet and the standard allows for the phy to be adapted to application requirements ...  the requirements for an office are different than a car so there are people working on the car application requirements now.   But  if that get's resolved - think about how many people in the industry already understand ethernet (or CAN) v.s. how many people understand FlexRay.   Again just my own opinion and advice - you need to make up your own mind and this forum is really for technical support more than advice - so I should keep quiet ;)

  • 0 in reply to Anthony F. Seely
    Intellectual 715 points

    Hello,

    Thank you very much for your insights on this matter. I was just curious which is why I inquired. I have to first configure the Flexray module and test the system before thinking about Ethernet.

    Original question here is a technical one, I am reading the Flexray Specification and I will be able to find the answer to my questions within next couple of days. 

    I am also familiar with Ethernet, but I am not the person who decides which protocol to use. I will definitely suggest Ethernet, but still I am too inexperienced to change the architecture. 

    Moving back to the original question, if there is anyone who can help me, it would be highly appreciated.

  • 0 in reply to Pradeepa Senanayake
    TI__Guru 68920 points
    Hi Pradeepa,

    I think we can help when it comes to how the IP integrates with the chip - but how the FlexRay bus works itself and how to set timings for the bus ... that's something that is too application specific and since it's not used by many customers we don't have a lot of experience with it. The training slides you already saw are probably the extent of what we've got in terms of ability to support FlexRay in general.

    You should probably search not for TI Hercules & FlexRay but for some companies that specialize in communication. For example https://vector.com/ is a company that has tremendous expertise in these niche automotive protocols and they produce some great training materials, whitepapers, and I think they even have a full-page poster you can request that illustrates the FlexRay protocol.
    When it comes to how to use the bus - you'll get a lot more useful information from them I think.

    Also check Bosch's website as the IP originally is theirs and they may have more up to date expertise & whitepapers. One reason we buy this IP is we don't have the expertise to build it and it's important to have an IP that has been developed by experts so that it works well..

    But if you have some issue with interrupts, DMA transfers, IO pins, clock inputs, etc.. these are SOC integration issues and you should come here for help definitely.

    -Anthony