Can mhpmcounter21h be accessed from any privilege level?
No. The official CSR table lists mhpmcounter21h as an RV32-only Machine read/write CSR.
CSR Bit Fields
RISC-V mhpmcounter21h CSR Register
Address 0xB95Privilege MachineAccess RW / RV32 high-half / 32-bitMachine counters and performance-monitoring CSRs
mhpmcounter21h at 0xB95 is the RV32 machine high-half CSR for bits 63:32 of mhpmcounter21.
Bit Overview
Hover for details · Click to jumpbit 3 = only bit 3; bits 12..11 = bits 12 down to 11
MSBLSB
Field Map
Understand mhpmcounter21h By Bit Fields
0 key fields
Official Basis & Search Notes
mhpmcounter21h is the RV32 high-half access CSR for bits 63:32 of mhpmcounter21; its event meaning is still determined by mhpmevent21.
mhpmcounter21 is a WARL register with up to 64 bits of precision; RV32 accesses it through low/high halves mhpmcounter21/mhpmcounter21h.
On RV32, the high-half CSR accesses bits 63:32 and the low-half CSR accesses bits 31:0.
mhpmcounter21h does not select the event; event selection is in mhpmevent21.
What To Check First When Reading This CSR
- - mhpmcounter21h exists only on RV32.
- - mhpmcounter21 is a WARL register with up to 64 bits of precision; event meanings are platform-defined.
- - mcountinhibit.HPM21 controls only whether mhpmcounter21 increments, not its accessibility.
Risk Checks Before Writing
- - On RV32, writing mhpmcounter21h changes only bits 63:32 of mhpmcounter21.
- - A legal implementation may make both mhpmcounter21 and its mhpmevent21 selector read-only zero.
Put It Back Into A Real Flow
1
On RV32, access mhpmcounter21h and mhpmcounter21 separately.
2
The high and low halves correspond to bits 63:32 and 31:0 of one WARL counter.
3
Use mhpmevent21 to determine the platform-selected event for the counter.
FAQ
Is mhpmcounter21h a separate counter?
No. It is only the RV32 access CSR for the upper 32 bits of mhpmcounter21.