RISC-V Design · All levels
CSR Programming Model, Privilege Visibility, and Timer Facilities: Theory Deep Dive
Theory Deep Dive for CSR Programming Model, Privilege Visibility, and Timer Facilities.
Theory deep dive
Theory Deep Dive for CSR Programming Model, Privilege Visibility, and Timer Facilities is anchored on CSR read/write hazard rate, timer interrupt accuracy (ns error), and software context-switch overhead attributable to CSR traffic.. Convert observations into mechanism-backed decisions with explicit ownership.
Theory matters when it predicts engineering outcomes. Tie abstract ISA and microarchitecture concepts to measurable behavior in trace and counter data.
Pipeline model
diagram
RISC-V PIPELINE DIAGRAM - CSR Programming Model, Privilege Visibility, and Timer Facilities
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 predictablePrivilege model
diagram
PRIVILEGE MODE STACK - CSR Programming Model, Privilege Visibility, and Timer Facilities
+------------------------------+
| Machine mode (M) |
| firmware, PMP, trap root |
+---------------+--------------+
|
delegated traps
v
+------------------------------+
| Supervisor mode (S) |
| kernel, page tables, drivers |
+---------------+--------------+
|
ecall / syscall
v
+------------------------------+
| User mode (U) |
| applications, libraries |
+------------------------------+
Key rule: each upward transition records cause + PC in trap CSRs.