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This is not forwards compatible. Debuggers that rely on haltsum0 would break with this change. But it makes the debug interface on tiny 1-hart systems smaller, especially because it allows the number of address bits in the DMI to be 1 less. (Haltsum0 at 0x40 due to other efforts to maintain backwards compatibility.) Fixes #389.
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@markuslauterbach, can you comment? |
| is halted or not. Unavailable/nonexistent harts are not considered to | ||
| be halted. | ||
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| This register may not be present in systems with fewer than 2 harts. |
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"May not" is ambiguous, possibly meaning "shall not" and possibly meaning "may." How about something like:
This register must be present in systems with 2 or more harts and may be in systems with 1 hart.
Also, is this statement related to the number of harts in the system or the number of harts attached to this DM?
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Does "might not" instead of "may not" work?
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That sounds good.
My other question still applies. Should it be something like "This register might not be present if fewer than 2 harts are attached to the DM." or do you think it's correct as written?
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You are right on that point. I've pushed a change to reflect all this.
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I can't really comment on whether it's justified to make a backwards-incompatible change here, but I agree that the change itself would be reasonable. So far my debug driver does not use haltsum at all. |
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Thank you, @markuslauterbach. Knowing it won't be a problem for you either makes me more confident that this change is OK. |
ernie-sifive
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ernie-sifive
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That wording sounds good to me.
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This is not forwards compatible. Debuggers that rely on haltsum0 would
break with this change. But it makes the debug interface on tiny 1-hart
systems smaller, especially because it allows the number of address bits
in the DMI to be 1 less. (Haltsum0 at 0x40 due to other efforts to
maintain backwards compatibility.)
Fixes #389.