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DM should ignore some bits while abstract command is executing #1046

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merged 5 commits into from
Jul 23, 2024
Merged

DM should ignore some bits while abstract command is executing #1046

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ca36be7
DM may ignore things when dmactive is changing.
rtwfroody Jun 13, 2024
7acbfa2
Hardware can ignore some bits during abstract command
rtwfroody Jul 11, 2024
2637350
Make language more clear
rtwfroody Jul 12, 2024
d84c6a8
should -> must
rtwfroody Jul 15, 2024
02a164f
Remove special behavior when dmactive is written low.
rtwfroody Jul 19, 2024
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2 changes: 2 additions & 0 deletions debug_module.adoc
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Original file line number Diff line number Diff line change
Expand Up @@ -369,6 +369,8 @@ of {dm-data0}) or hart (e.g. contents of a register modified by a Program Buffe
Before starting an abstract command, a debugger must ensure that {dmcontrol-haltreq}, {dmcontrol-resumereq}, and {dmcontrol-ackhavereset} are all 0.

While an abstract command is executing ({abstractcs-busy} in {dm-abstractcs} is high), a debugger must not change {hartsel}, and must not write 1 to {dmcontrol-haltreq}, {dmcontrol-resumereq}, {dmcontrol-ackhavereset}, {dmcontrol-setresethaltreq}, or {dmcontrol-clrresethaltreq}.
The exception to this rule is when 0 is written to {dmcontrol-dmactive}, in
which case the DM may ignore all bits other than {dmcontrol-dmactive}.

If an abstract command does not complete in the expected time and
appears to be hung, the debugger can try to reset the hart (using {dmcontrol-hartreset} or {dmcontrol-ndmreset}).
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6 changes: 5 additions & 1 deletion xml/dm_registers.xml
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Expand Up @@ -340,13 +340,17 @@ same project unless stated otherwise.
state change has completed. Hardware may
take an arbitrarily long time to complete activation or deactivation and will
indicate completion by setting {dmcontrol-dmactive} to the requested value.
During this time, the DM may ignore any register writes.

<value v="0" name="inactive">
The module's state, including authentication mechanism,
takes its reset values (the {dmcontrol-dmactive} bit is the only bit which can
be written to something other than its reset value). Any accesses
to the module may fail. Specifically, {dmstatus-version} might not return
correct data.

When this value is written, the DM may ignore any other bits written
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to {dmcontrol} in the same write.
</value>

<value v="1" name="active">
Expand All @@ -356,7 +360,7 @@ same project unless stated otherwise.
No other mechanism should exist that may result in resetting the
Debug Module after power up.

To place the Debug Module into a known state, a debugger may write 0 to {dmcontrol-dmactive},
To place the Debug Module into a known state, a debugger should write 0 to {dmcontrol-dmactive},
poll until {dmcontrol-dmactive} is observed 0, write 1 to {dmcontrol-dmactive}, and
poll until {dmcontrol-dmactive} is observed 1.

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