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SWO and variables reading

Pietsuro Botsutoshi
Note: This was originally posted on 27th February 2012 at http://forums.arm.com

Dear all,

I would like to create a SWV application, and my question is the following: how many variables can I read via SWO communication?

I mean, without considering the overflow packet that could be sent in case of huge information traffic, is there a physical limit regarding this topic?

If I've understood weel, DWT_COMPx registers, with x={1, .., 4} is used in order to store the variable address that I would like to monitor, and DWT_MASKx are also used in order to raise a valid new SWO packet.

Does this mean that it's possible to check only for four variables, or should I set the mask register in order to detect ranges of variables?
With the latter case I could be able to monitor a very large number of items.

Am I wrong or is this the right approach?

Thank you very much!
Parents
  • Arm Employee Badge
    Note: This was originally posted on 10th April 2012 at http://forums.arm.com

    Hi,

    Sorry for the delay. I was having a very busy schedule last week.

    Try think of it as bit stream
    The sync packet is 47 bit of 0 followed by a 1.
    Depends on your synchronization situation before you get the first byte, you might have already missed 7 bit of zeros which was merged into last bytes.

    Then you get 1 byte of zeros (8 bits), so you get minimum of 4 bytes of sub sequence zeros.
    Then you will get things like
    xxxxxxx1, or
    xxxxxx10, or
    xxxxx100, or
    ...
    10000000

    If MASK size is set to 0x2 (word size), the address value set in COMPx must be multiple of word size.
    So your solution does not work.
    regards,
    Joseph
    P.S. I am out of office next two weeks.
Reply
  • Arm Employee Badge
    Note: This was originally posted on 10th April 2012 at http://forums.arm.com

    Hi,

    Sorry for the delay. I was having a very busy schedule last week.

    Try think of it as bit stream
    The sync packet is 47 bit of 0 followed by a 1.
    Depends on your synchronization situation before you get the first byte, you might have already missed 7 bit of zeros which was merged into last bytes.

    Then you get 1 byte of zeros (8 bits), so you get minimum of 4 bytes of sub sequence zeros.
    Then you will get things like
    xxxxxxx1, or
    xxxxxx10, or
    xxxxx100, or
    ...
    10000000

    If MASK size is set to 0x2 (word size), the address value set in COMPx must be multiple of word size.
    So your solution does not work.
    regards,
    Joseph
    P.S. I am out of office next two weeks.
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