pcb_psr
int pcb_psr; /* %psr when switch() was called */
snprintb(bits, sizeof(bits), PSR_BITS, pcb->pcb_psr);
if (pcb && pcb->pcb_psr == 0)
pcb->pcb_psr = getpsr();
opcb->pcb_psr = getpsr();
npcb->pcb_psr &= ~PSR_CWP; /* Run in window #0 */