MUSB_TXINTERVAL
musb_readb(epio, MUSB_TXINTERVAL);
musb_writeb(epio, MUSB_TXINTERVAL,
musb_writeb(epio, MUSB_TXINTERVAL, 0);
musb_writeb(epio, MUSB_TXINTERVAL, qh->intv_reg);
#define MUSB_NAKLIMIT0 MUSB_TXINTERVAL /* Re-used for EP0 */