APB协议学习

APB主要用来连接高性能低带宽的外围设备，在APB总线系统中，只有一个master，其他的都是slave。一般情况下，APB挂在AHB总线系统下，通过AHB-APB Bridge将事务在AHB总线系统之间进行转化，此时Bridgre即为APB的master，其他的外围设备均为slave。

APB协议学习

• Introduction
  • The APB protocol is not pipelined
  • Every transfer takes at least two cycles
• Write transfers
  • With no wait states
  • With wait states
    • PREADY can take any value when PENABLE is LOW.
    • Note:It is recommended that the address and write signals are not changed immediately after a transfer, but remain stable until another access occurs. This reduces power consumption.
• Read transfers
  • With no wait states
  • With wait states
• Error response
  • PSLVERR is only considered valid during the last cycle of an APB transfer, when PSEL, PENABLE, and PREADY are all HIGH.
  • Write transfer
  • Read transfer
• Protection