arch-riscv: Add NMI support
NMI is platform dependent according to riscv spec, so we intentionally
propose a very minimal design that doesn't give user any new accessible
register to interact with the NMI mechanism.
In current design, the NMI reset vector is fixed to 0x0 and always set
mcause to zero. mret from NMI handler is still possible, but it's up to
the user to detect whether a M-mode trap handler is interrupted and to
recover from it (if at all possible).
1. Add new fault type to represent NMI fault
2. Add non-standard registers to save the status of NMI
a. nmivec[63:2] = NMI reset vector address
b. nmie[0:0] = is NMI enabled = not in NMI handler
c. nmip[0:0] = is NMI pending
3. Add new function in RiscvInterrupts to raise/clear NMI
Bug: 200169094
Test: None
Change-Id: Ia81e1c9589bc02f0690d094fff5f13412846acbe
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/52363
Reviewed-by: Yu-hsin Wang <yuhsingw@google.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
6 files changed
