NMI spec updates: removed UNMI, added new mnie bit to mnstatus #2904
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ingallsj
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ernie-sifive
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Nov 11, 2021
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Related issue:
Type of change: bug report | feature request | other enhancement
Impact: API modification
Development Phase: implementation
Release Notes
The NMI arch spec is being prepared for submission to RISC-V International. As part of that, the UNMI feature has been removed from it. External IO unmi_* were removed and all internal implementation referring to unmi was removed. Most changes are in the CSR modules where NMI is processed.
The latest NMI spec has added a bit
mnie(notnmie) tomnstatus. This bit reflects the internalrnmiestate.rnmieis set at reset, is cleared when an NMI is taken, and is set by executingmnretat the end of the NMI handler (unchanged by this PR). Nowrnmiecan also be read and set by software so that nested NMIs can be processed.rnmiecannot be cleared by software, per the spec.The mnstatus register read value was using
io.status.mpp(=mstatus.mpp) instead ofmnstatus.mpp.