SSTC extension allows nuttx to implement S-mode timer directly,
which is useful for starting at S-mode.
Signed-off-by: Inochi Amaoto <inochiama@outlook.com>
Using CSR name depends on compiler support heavily, but CSR
encoding does not have this problem. It also make it easy to
add new CSR support even if the compiler does not support.
Unify CSR access by using the CSR encoding macro.
Signed-off-by: Inochi Amaoto <inochiama@outlook.com>
- Add config "ARCH_USE_S_MODE" which controls whether the kernel
runs in M-mode or S-mode
- Add more MSTATUS and most of the SSTATUS register definitions
- Add more MIP flags for interrupt delegation
- Add handling of interrupts from S-mode
- Add handling of FPU from S-mode
- Add new context handling functions that are not dependent on the trap
handlers / ecall
NOTE: S-mode requires a companion SW (SBI) which is not yet implemented,
thus S-mode is not usable as is, yet.
