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TMS320F280049C: LIN auto baud rate

Angela Zou
Intellectual 885 points
Part Number: TMS320F280049C

Hi experts,

BU offered a demo software of auto baud rate.    

There is an issue when my customer is testing the auto baud rate of LIN. It only works in a certain range at 17.6Kbps~19.23Kbps. The baud rate seems to be limited. For example, when setting the baud rate as 10.417kbps, the LIN communication is disconnected. I see the description of the MBRSR in the manual,  whether an update to the MBRSR is required? I mean does this API need to be updated all the time? For example, if the frequency changes, does he need to update this maximum baud rate limit in main-loop?

 

Another question is in the following description,  what is the meaning of 10%? Is that mean the baud rate of master must be more than MBRSR*10%? Or anything else?  

  • 0
    TI__Genius 15385 points

    Hi Zou,

    I am looking into this and discussing with experts within the team to understand the implementation of Automatic baud rate. Let me get back to you by end of this week.

    Best Regards,

    Nirav

  • 0 in reply to Nirav Ginwala
    TI__Genius 15385 points

    Hi Zou,

    Please find below response to your questions:

    For example, when setting the baud rate as 10.417kbps, the LIN communication is disconnected. I see the description of the MBRSR in the manual,  whether an update to the MBRSR is required?

    -- Yes, MBRSR needs to be configured to max  of 10% of the operating Baud Rate.

    I mean does this API need to be updated all the time? For example, if the frequency changes, does he need to update this maximum baud rate limit in main-loop?

    -- Yes, LIN in slave mode should know what the operating baud rate is and needs to configure MBRSR to max of that value.

    Another question is in the following description,  what is the meaning of 10%? Is that mean the baud rate of master must be more than MBRSR*10%? Or anything else?  

    - When LIN is configured in Adaptive mode, MBRSR needs to be configured 10% higher than actual / incoming baud rate. Baud rate of the Master has to be within 10% of operating baud rate. Meaning if expected baud rate from Master is x, MBRSR needs to be configured to 1.1*x (10%). More than 10% is not allowed. And transmitting baud rate by master has to be within this 10% window. LIN in adaptive baud rate configuration can only tune to incoming baud rate in this 10% window, outside this window it will not detect package and will not work.

    Best Regards,

    Nirav

  • 0 in reply to Nirav Ginwala
    Prodigy 60 points

    Hi Nirav,

    This is Haisong. Thanks for your feedback.

    Assuming that if the master baud rate is 15Kbps, the MBRSR should be set to 16.5Kbps based on your description, I think. If we don't update the MBRSR, when the master baud rate is changed from 15Kbps to 12Kbps, what will happen on LIN commucation? Another situation is that if we don't update the MBRSR, when the master baud rate is changed from 15Kbps to18Kbps, what will happen on LIN commucation?

  • 0 in reply to user5008793
    TI__Genius 15385 points

    Hi Haisong,

    Any baud rate change outside 10% of configured MBRSR value will not work without updating MBRSR value to new max value.

    Answer to both your questions is No.

    Before baud rate is reduced to 12Kbps from 15kbps, MBRSR needs to be configured to 13.2kbsp.

    Similarly, before baud rate is increased from 15kbps to 18kbps, MBRSR needs to be configured to 19.8kbsp.

    Best Regards,

    Nirav

  • 0 in reply to Nirav Ginwala
    Prodigy 60 points

    Hi Nirav,

    Actually, I have tried to set the max baud rate as 17Kbps by configuring the MBRSR. And I have tested the baud rate as the range from 19.32Kbps t0 15Kbps. The LIN communication is working normally. But when the baud rate is lower than 15Kbps, LIN communication will be failed. Can you help me to explain these two cases? As you said, when any baud rate change outside 10% of MBRSR, the LIN will not work. Our test result didn't agree with what you said.

    Can you help to test our cases in your side?

  • 0 in reply to user5008793
    TI__Genius 15385 points

    Hi,

    Can you please provide more details on configured MBR value when baud rate is less than 15kbps, where you see LIN communication failing?

    If you can share different configuration that you tested with the results seen that will help us try it out at our end.

    We did try below 15kbps with MBR value set to 10% of operating baud rate, and it worked. It will be good if you can give specific configuration for us to check.

    Best Regards,

    Nirav

  • 0 in reply to Nirav Ginwala
    Prodigy 60 points

    Ok, Nirav.

    So firstly, you can set the MBR as 17Kbps. So why the LIN can work with 19.23Kbps? I think this is already beyond the 10% of 17Kbps.

    Can you give me an explanation?

  • 0 in reply to user5008793
    TI__Genius 15385 points

    Hi,

    Yes I have seen similar results on my setup as well, where it can work beyond 10% operating baud rate, that may be due to delays associated with synchronizers in the path, but by design it is guranteed to work at 10%. So we do not recommend to configure Max BR beyond 10% because synchronizer delay can vary across operating conditions and may not work beyond 10%.

    Best Regards,

    Nirav