CSR_VSTIMECMPH
ncsr_write(CSR_VSTIMECMPH, (u32)(t->next_cycles >> 32));
t->next_cycles |= (u64)ncsr_read(CSR_VSTIMECMPH) << 32;
csr_write(CSR_VSTIMECMPH, -1UL);
ncsr_write(CSR_VSTIMECMPH, ncycles >> 32);