code так может - в документации об этом не слова.
While CSRs are primarily used by the privileged architecture, there are several uses in
unprivileged code including for counters and timers, and for floating-point status.
The counters and timers are no longer considered mandatory parts of the standard base
ISAs, and so the CSR instructions required to access them have been moved out of Chapter
2 into this separate chapter.
if (write && csr_read_only)
throw trap_illegal_instruction(insn.bits());