OHCI_IROFF
off = OHCI_IROFF(dmach);
#define OHCI_IRCTL(CH) (OHCI_IROFF(CH))
#define OHCI_IRCTLCLR(CH) (OHCI_IROFF(CH) + 4)
#define OHCI_IRCMD(CH) (OHCI_IROFF(CH) + 0xc)
#define OHCI_IRMATCH(CH) (OHCI_IROFF(CH) + 0x10)