BT848_RISC_VBI
#define BT848_INT_RISCS_VBI (BT848_RISC_VBI << 28)
btv->loop_irq |= BT848_RISC_VBI;
btv->loop_irq &= ~BT848_RISC_VBI;
btv->loop_irq = BT848_RISC_VBI;