RISC-V mhpmcounter9 CSR Register

Address 0xB09Privilege MachineAccess RW / Up to 64-bit precisionMachine counters and performance-monitoring CSRs

mhpmcounter9 at 0xB09 is machine hardware performance-monitor counter 9, with up to 64 bits of precision for the event selected by mhpmevent9.

Related Search Terms

mhpmcounter9 CSR mhpmcounter9 0xB09 HPM counter 9 mhpmevent9 event machine performance counter up to 64-bit precision

Bit Overview

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bit 3 = only bit 3; bits 12..11 = bits 12 down to 11

MSBLSB

COUNT63:0RW

Field Map

Understand mhpmcounter9 By Bit Fields

1 key fields

63:0

COUNT

Machine HPM count for the event selected by mhpmevent9; this is a WARL register with up to 64 bits of precision, and a legal implementation may make it and the corresponding mhpmevent9 selector both read-only zero.

COUNT (bits 63:0) — Machine HPM count for the event selected by mhpmevent9; this is a WARL register with up to 64 bits of precision, and a legal implementation may make it and the corresponding mhpmevent9 selector both read-only zero.

What This Field Controls

- Machine HPM count for the event selected by mhpmevent9; this is a WARL register with up to 64 bits of precision, and a legal implementation may make it and the corresponding mhpmevent9 selector both read-only zero.

Common Values

This field is better understood together with surrounding context than as a fixed memorized enumeration.

Official Basis & Search Notes

mhpmcounter9 is machine HPM counter 9. It does not define event meaning itself; with up to 64 bits of precision, it counts the platform-defined event currently selected by mhpmevent9.

The official machine HPM mechanism defines mhpmcounter9 as a WARL counter with up to 64 bits of precision.

mhpmevent9 selects the event; event meaning is platform-defined, and event 0 means "no event".

On RV32, mhpmcounter9h accesses bits 63:32; a legal implementation may make both mhpmcounter9 and mhpmevent9 read-only zero.

RISC-V Privileged Architecture Manual: CSR Listing RISC-V Privileged Architecture Manual: Machine-Level ISA

What To Check First When Reading This CSR

- The event source for mhpmcounter9 is selected by mhpmevent9; event meaning is platform-defined.
- S/U-mode reads of the read-only hpmcounter9 view are controlled by mcounteren.HPM9; U-mode is additionally controlled by scounteren.HPM9.
- On RV32, mhpmcounter9h accesses bits 63:32 of mhpmcounter9.

Risk Checks Before Writing

- Writing mhpmcounter9 changes its current count; a CSR write takes effect after the writing instruction has otherwise completed.
- mcountinhibit.HPM9 controls whether this counter increments, not its accessibility.
- This counter and mhpmevent9 are WARL; event encodings are platform-defined, and event 0 means "no event".

Put It Back Into A Real Flow

Configure mhpmevent9 to select the platform-defined event to count.

Set mcountinhibit.HPM9 when needed to stop mhpmcounter9 from incrementing.

Read mhpmcounter9; on RV32, also read mhpmcounter9h to obtain the value with up to 64 bits of precision.

FAQ

Can mhpmcounter9 be accessed from any privilege level?

No. The CSR table lists mhpmcounter9 as a machine read/write CSR. Lower-privilege access is to the corresponding read-only hpmcounter9 view: S/U-mode reads are controlled by mcounteren.HPM9, and U-mode reads are additionally controlled by scounteren.HPM9. A disallowed read raises an illegal-instruction exception.

How is mhpmcounter9 related to hpmcounter9?

mhpmcounter9 is the machine read/write counter; hpmcounter9 is its corresponding lower-privilege read-only shadow. S/U-mode reads are controlled by mcounteren.HPM9, and U-mode reads are additionally controlled by scounteren.HPM9.