[BUG] : mip.MSIP and mie.MSIE are read-only zeros

[AyoubJalali]

Is there an existing CVA6 bug for this?

• I have searched the existing bug issues

Bug Description

According to CV32A65X Spec, As the system has only one hart then mip.MSIP and mie.MSIE are read-only zeros.

So there's a bug on RTL, it allow modifying mip.MSIP and mie.MSIE

[JeanRochCoulon]

This issue has not been detected up-to-now, the reason is maybe linked to the fact that Spike get the same RTL behavior allowing to modify mip.MSIP and mie.MSIE. So, there' maybe a bug in Spike.

[AyoubJalali]

This issue has not been detected up-to-now, the reason is maybe linked to the fact that Spike get the same RTL behavior allowing to modify mip.MSIP and mie.MSIE. So, there' maybe a bug in Spike.

I opened an issue on core-v-verif related to the same bug in (openhwgroup/core-v-verif#2531)

[zchamski]

When building the mask of modifiable mie bits at https://github.com/openhwgroup/cva6/blob/master/core/csr_regfile.sv#L1440, the mask for bit mie.MSIE should only be set if the configuration of the core supports multi-core setups.

[JeanRochCoulon]

This issue is present in both Spike and RTL. It was hidden by SpikeTandem

[zchamski]

The Spike side was fixed in #2523. The remaining action is to update the RTL and add an appropriate RTL configuration parameter, as pointed out by @AyoubJalali.

[valentinThomazic]

The CSR embedded regression test is failing because of this.
Mismatch example :

mismatch_description: 'CSR 304  Mismatch   [REF]: 0x880              [CORE]: 0x888             '
mismatches:
- 0: null
  core:
    insn: 0000000030419073
    insn_disasm: csrrw   zero, mie, gp
    mode: 3
    pc_rdata: 00000000800036ac
    pc_wdata: 0
    rd1_addr: 0
    rd1_rdata: 0
    rs1_addr: 3
    rs1_rdata: 0000000000000008
    rs2_addr: 4
    rs2_rdata: 196
    trap: 0
  reference_model:
    insn: 0000000030419073
    insn_disasm: csrrw   zero, mie, gp
    mode: 3
    pc_rdata: 00000000800036ac
    pc_wdata: 0
    rd1_addr: 0
    rd1_rdata: 0
    rs1_addr: 3
    rs1_rdata: 0000000000000008
    rs2_addr: 4
    rs2_rdata: 0000000080000000
    trap: 0

This should be resolved as soon as the RTL is aligned on Spike