RMIXL_PIC_IRTENTRYC0
c0 = RMIXL_PICREG_READ(RMIXL_PIC_IRTENTRYC0(irt));
RMIXL_PICREG_WRITE(RMIXL_PIC_IRTENTRYC0(irt), 0); /* low word */
KASSERT(RMIXL_PICREG_READ(RMIXL_PIC_IRTENTRYC0(irt)) == 0);
RMIXL_PICREG_WRITE(RMIXL_PIC_IRTENTRYC0(irt), irtc0); /* low word */