Interrupt control and state register
| VECTACTIVE | Active vector |
| RETTOBASE | Return to base level |
| VECTPENDING | Pending vector |
| ISRPENDING | Interrupt pending flag |
| PENDSTCLR | SysTick exception clear-pending bit |
| PENDSTSET | SysTick exception set-pending bit |
| PENDSVCLR | PendSV clear-pending bit |
| PENDSVSET | PendSV set-pending bit |
| NMIPENDSET | NMI set-pending bit. |