AMBA_Bus_transfer_3

Split transfer

Split 이란 bus master 가 bus를 사용하고 있다가, operation 이 시작될때 까지 많이 걸리겠다 판단되면 bus 를 잠시 다른 master 에게 빌려주는거다. bus의 utilization 을 높이는 일이지.

split 의 과정이다. 해석하면 이상하니까 영어로 그대로

1. The master starts the transfer in an identical way to any other transfer and issues address and control information.

2. If the slave is able to provide data immediately it may do so. If the slave decides that it may takes a number of cycles, it gives a SPLIT transfer response.

During every transfer the arbiter broadcasts a number, or tag, showing which master is using the bus.

3. The arbiter grants other masters use of the bus and the action of the SPLIT response allows bus master to handover to occur.

4. When the slave is ready to complete the transfer it asserts the appropriate bit of HSPLITx bus to indicate which master should be regranted access to the bus

5. The arbiter observes the HSPLITx signals on every cycle, and when any bit of HSPLITx is asserted the arbiter restores the priority of the appropriate master

6. Eventually the arbiter will grant  the master so it can re-attempt the transfer. This may not occur immediately if a higher priority master is using the bus.

밑에는 예시이다...........

1. slave 가 뭔가 시간이 걸리겠구나 판단을 해서 2-cycle split 을 response 로 내놓음

2. rising edge 에서 split response 를 catch 하고 IDLE 을 넣어줌

3. B 모드로 바뀜