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'c5515 Address of DBSTAT

Hello All,

What is the address of DBSTAT on the 'c5515 - it is mentioned on page 4-8 in the CPU v3.x C55 UG - in Section 4.4 Automatic Context Switching.  It says DBSTAT is a DSP register but I don't find it in Table 2-2 in section 2.2.

Thanks,
John W.

 

  • John,

    After checking with my colleagues, this is a status register used during emulation. It is no longer supported.  It  has been marked for removal and will be removed from future spec.

    Regards,

    Steve

  • Hello Steve,

    What about DBSTAT during automatic context switching - it is still pushed to SSP - correct?  Or not?  And if not - can you give an update on what the stack looks like during automatic context switches?

    Thanks,
    John W. 

  • Hello John,

    Since this register is no longer supported, it is not accessiable at all.

    Regards,

    Steve

  • Hello Steve,

    So, DBSTAT isn't pushed/popped to/from SSP anymore then, correct?

    So, what does the stack frame look like now, i.e. - in the CPU v3.3 doc - how are sections 4.4.2 and 4,4,4 updated?

    Thanks,
    John W.

  • John W,

    SP & SSP registers are accessible under CPU registers.

    Regards,

    Steve

  • The DBSTAT register is used by the TI emulator-based debug tools.  It is reserved for TI and is not available to end users.  It is saved/restored on interrupts, so the pictures as shown are accurate.

    I am not aware of anything about "no longer supported" or "removed from future spec".   I wonder if Steve and I are talking about the same thing.

    In any case, the stack frame descriptions are correct as given in the manual.

     

     

  • Paul,

    Thank you for the clarification. I meant DBSTAT is reserved for TI and is not supported for end user to chnage.

    Thanks,

    Steve 

  • Steve,

    I thought that might have been what you meant.  I suspected that the "removed from future spec" statement just meant that explicit mention of DBSTAT in the manual will be removed.  The register will still be there, will be saved on the stack, etc.  We just won't pique a user's curiosity with the obscure reference.

     

  • Paul & Steve,

    Hmmm, this is a little disturbing to me.  Since TI is allowing end-users to add their own O/S now and not force-feeding DSP/BIOS anymore, or at least I think this is the case, knowing *exactly* what the stack frame looks like is very important.  I need to know the exact definition of the stack, both SP and SSP at all times.

    I think it'll be more confusing if an end-user sees SSP mysteriously increment and decrement without knowing what is going on.  In my case, I will need to relocate(save) DBSTAT - not change it; to make sure it is restored properly.  I don't know why TI doesn't want to fully open the kimono here. 

    I suppose DBSTAT is only utilized during debug, and not during normal execution; so that will have to be taken into account as well.

    Of course I am referring to the removal of DBSTAT from the ref. manuals even though it will be 'there'.  Someone doing a stack-frame 'fix-up' will find their debugger(s) breaking mysteriously if the reference is removed.

    Thanks,
    John W.

  • I can agree that any change to the manual should make clear 1) exactly what the stack frame layout is (and I think the current manual does that), and 2) that the "mystery word" (which I assume would still say something about "reserved for TI" or "reserved for hardware debug" or some such) must be left unmolested (or not?), and perhaps say something about being unused if no hardware debug is active (_IF_ that is the case, and I personally do not know if that is the case).  My guess, and it is only a guess, is that the meaning of particular bits in that word depends on what emulator is in play.

     

  • Hello Paul,

    Fair enough - as long as the stack frame is accurate - even if it says 'reserved for TI' or something to that effect; that will be better than figuring out the hard way why SSP was pushed or popped out from under you.

    Thanks,
    John

    BTW - 'slow' stack frame mode really isn't 'slow'...;)

     

  • Hello All,

    Ha! Here I am again - and DBSTAT is an issue for me in a port for the 'C5535. So, can I get any specifics on DBSTAT?

    I have my port running; but I seem to be unwittingly forcing the processor into single step mode; can I get some info and get this resolved?

    The stack frame information is the same - correct?

    Thanks!
    John W.