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Explained which addresses are used as compare values for execute/load… #585

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Jun 14, 2022
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Explained which addresses are used as compare values for execute/load… #585

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6 changes: 6 additions & 0 deletions docs/user_manual/source/debug.rst
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Expand Up @@ -34,6 +34,12 @@ The |corev| also supports a Trigger Module to enable entry into Debug Mode on a
- Number of trigger register(s): Parametrizable number of triggers using parameter ``DBG_NUM_TRIGGERS``.
- Supported trigger types: Execute/load/store address match (Match Control) and exception trigger.

The compare value used to determine an execute address match is the PC of the instruction, i.e. only the lowest virtual address
of the instruction is used. The compare value(s) used to determine a load/store address match depend(s) on the size of the transferred
data item as well as the lowest virtual address of the access. A byte load/store for address ``A`` only uses ``A`` as compare value; a
halfword load/store for address ``A`` uses ``A`` and ``A+1`` as compare values; a word load/store for address ``A`` uses ``A``, ``A+1``,
``A+2`` and ``A+3`` as compare values.

A trigger match will cause debug entry if ``tdata1.ACTION`` is 1.

The |corev| will not support the optional debug features 10, 11, & 12 listed in Section 4.1 of [RISC-V-DEBUG]_. Specifically, a control transfer instruction's destination location being in or out of the Program Buffer and instructions depending on PC value shall **not** cause an illegal instruction.
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