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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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  • Note: This was originally posted on 26th March 2012 at http://forums.arm.com

    Ciao Joseph, thank you again for your support.

    Considering the available documentation, 0x0000000D and 0x0000000E values for DWT_FUNCTIONx are set as reserved.
    Am I reading an old release?

    In any case, I'm not able to read SWO packets with only write information for the registered variable, but only tons of local timestamps (with value 1999999).

    This is my activation flow:

    • DWT_CTRL = 0x400003FE
    • DWT_COMP0= 0x2000017C
    • DWT_MASK0 = 0x00000001
    • DWT_FUNCTION0 = 0x0000000D
    • DEMCR = 0x01000000
    • SELECTED_PIN_PROTOCOL_REGISTER = 0x00000002
    • TPIU_ACPR= (72000000 / 500000) - 1
    • ITM_LOCK_ACCESS_REGISTER = 0xC5ACCE55
    • ITM_TCR = 0x0001000F
    • ITM_TPR = 0x0000000F
    • ITM_TER = 0x00000000
    • TPIU_FFCR = 0x00000100
    The address of the variable to read is 0x2000017C and it represents an unsigned short value, so 2 bytes-length.

    Any idea?

    Thank you again.
Reply
  • Note: This was originally posted on 26th March 2012 at http://forums.arm.com

    Ciao Joseph, thank you again for your support.

    Considering the available documentation, 0x0000000D and 0x0000000E values for DWT_FUNCTIONx are set as reserved.
    Am I reading an old release?

    In any case, I'm not able to read SWO packets with only write information for the registered variable, but only tons of local timestamps (with value 1999999).

    This is my activation flow:

    • DWT_CTRL = 0x400003FE
    • DWT_COMP0= 0x2000017C
    • DWT_MASK0 = 0x00000001
    • DWT_FUNCTION0 = 0x0000000D
    • DEMCR = 0x01000000
    • SELECTED_PIN_PROTOCOL_REGISTER = 0x00000002
    • TPIU_ACPR= (72000000 / 500000) - 1
    • ITM_LOCK_ACCESS_REGISTER = 0xC5ACCE55
    • ITM_TCR = 0x0001000F
    • ITM_TPR = 0x0000000F
    • ITM_TER = 0x00000000
    • TPIU_FFCR = 0x00000100
    The address of the variable to read is 0x2000017C and it represents an unsigned short value, so 2 bytes-length.

    Any idea?

    Thank you again.
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