MPU_INPUTBUSY
#define RXRDY(m) ( (STATUS(m) & MPU_INPUTBUSY) == 0)
#define D(x,l) kprintf("mpu401_intr %d %x %s %s\n",l, x, x&MPU_INPUTBUSY?"RX":"", x&MPU_OUTPUTBUSY?"TX":"")
while ((s & MPU_INPUTBUSY) == 0 && i < MPU_INTR_BUF) {