pready can take any value when penable is low.this ensures that peripherals that have a fixed two cycle access can tie pready high.前后两句因果关系是怎样的？尤其后面那句如何理解？
pready can take any value when penable is low.this ensures that peripherals that have a fixed two cycle access can tie pready high.前后两句因果关系是怎样的？尤其后面那句如何理解？
这句话的意思是，当penable为低的时候，pready可以是任意值。
如果外设（apb slave）是固定的两个周期的读写设备，也就是没有反压情况，那么就可以将pready一直置高，简化apb slave的处理。
