RISC-V Design ยท All levels
Privilege Levels, Execution Modes, and Delegation Boundaries: Worked Example
Worked Example for Privilege Levels, Execution Modes, and Delegation Boundaries.
Worked example
Worked Example for Privilege Levels, Execution Modes, and Delegation Boundaries is anchored on Privilege-transition latency and number of unauthorized accesses blocked by PMP/page-permission checks per billion instructions.. Convert observations into mechanism-backed decisions with explicit ownership.
A regression flags Privilege-transition latency and number of unauthorized accesses blocked by PMP/page-permission checks per billion instructions.. Strong closure isolates first failing mechanism, proves causality, applies one bounded change, and validates blast radius.
System view
RISC-V PIPELINE DIAGRAM - Privilege Levels, Execution Modes, and Delegation Boundaries
PC -> IF -> ID -> EX -> MEM -> WB
| | | | |
i-cache decode ALU/BR LSU regfile write
\ |
+-> branch resolve + redirect
Hot paths:
- branch + load-use dependencies in ID/EX
- memory latency stretching MEM stage
- writeback arbitration for integer/vector units
Focus: keep control hazards predictableEvidence matrix
RISC-V EVIDENCE MATRIX - Privilege Levels, Execution Modes, and Delegation Boundaries
+--------------------------+--------------------------------+--------------------------------+---------------------------+
| Evidence | Tells you | Does not prove | Next action |
+--------------------------+--------------------------------+--------------------------------+---------------------------+
| perf counter timeline | where regression appears | exact mechanism causality | correlate with trace |
| decode/control dump | control intent per instruction | pipeline side-effect ordering | inspect retire semantics |
| trap + CSR logs | privilege/fault behavior | performance bottleneck alone | pair with CPI buckets |
| MMU/TLB walk trace | translation behavior | full system QoS impact | test mixed workloads |
| post-fix trend graph | movement after fix | long-term stability | run stress matrix |
+--------------------------+--------------------------------+--------------------------------+---------------------------+Capture baseline and failing traces under fixed metadata tags.
Classify stage loss and dominant mechanism.
Collect Privilege-transition matrix covering entry source, target mode, delegated cause bits, and required state-save set..
Apply one bounded fix with owner signoff.
Run validation matrix and decide ship/rollback.