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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!
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  • Arm Employee Badge
    Note: This was originally posted on 27th March 2012 at http://forums.arm.com

    Not much really, apart from trying to run the SWO as fast as possible.

    If you use separated comparators (one comparator for one variable), you don't need to emit the address offset.
    If you use one comparator for multiple variables, you will need to emit the address offset so that you can tell which access is which data, so it will take more bandwidth.

    Also, if you have the timestamp is enabled it will also need more data bandwidth. So if the bandwidth is limited, then don't enable the timestamp packet generation.

    regards,
    Joseph
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  • Arm Employee Badge
    Note: This was originally posted on 27th March 2012 at http://forums.arm.com

    Not much really, apart from trying to run the SWO as fast as possible.

    If you use separated comparators (one comparator for one variable), you don't need to emit the address offset.
    If you use one comparator for multiple variables, you will need to emit the address offset so that you can tell which access is which data, so it will take more bandwidth.

    Also, if you have the timestamp is enabled it will also need more data bandwidth. So if the bandwidth is limited, then don't enable the timestamp packet generation.

    regards,
    Joseph
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