CSR_VSCAUSE
nacl_csr_write(nsh, CSR_VSCAUSE, csr->vscause);
csr_write(CSR_VSCAUSE, csr->vscause);
csr->vscause = nacl_csr_read(nsh, CSR_VSCAUSE);
csr->vscause = csr_read(CSR_VSCAUSE);
ncsr_write(CSR_VSCAUSE, trap->scause);