E2.9 Wake-up Signaling

The wake-up signals are used to indicate that there is activity associated with the interface. These are: • AWAKEUP. • ACWAKEUP. The Wakeup_Signals property is used to indicate whether a component supports wake-up signaling: TRUE Wake-up signals are supported. FALSE Wake-up signals are not supported. If Wakeup_Signals is not declared, it is considered FALSE. The signals can be routed to a clock controller, or similar component, to enable power and clocks to the connected components. The wake-up signals must be glitch-free and generated directly from a register. They are synchronous to the interface that it relates to, but are appropriate for crossing clock domains to a controller. Wake-up signals must be asserted to guarantee that a transaction can be accepted, but once the transaction is in progress the assertion or deassertion of the wake-up signal is IMPLEMENTATION DEFINED. This specification recommends, but does not require, that the wake-up signal be deasserted when no further transactions are required.

wake_up信号用于喚醒要通信的component，spec建議但不要求，當沒有transaction時，dessert wake_up信号。

E2.9.1 AWAKEUP rules and recommendations

AWAKEUP is an output signal from a master interface and is asserted at the start of a transaction to indicate that there is a transaction to be processed:	AWAKEUP是由master在開始傳輸時發出的
•This specification recommends that AWAKEUP is asserted at least one cycle before the assertion of ARVALID, AWVALID, or WVALID to prevent the acceptance of a new transaction being delayed.	建議AWAKEUP要比xVALID信号早一個時鐘發出，以免傳輸被delay。
•It is permitted for AWAKEUP to be asserted at any point before or after the assertion of ARVALID, AWVALID, or WVALID. • A slave is permitted to wait for AWAKEUP to be asserted before asserting ARREADY, AWREADY, or WREADY. • To ensure progress of the transaction, AWAKEUP must remain asserted until the associated ARVALID, ARREADY handshake, or the AWVALID, AWREADY handshake. • After the ARVALID, ARREADY handshake, or the AWVALID, AWREADY handshake, the interconnect must remain active until the transaction has completed.
• It is required that the AWAKEUP signal is asserted to guarantee progress of a transition on the Coherency Connection signaling. See Coherency Connection signaling on page E2-362: — It is permitted for AWAKEUP to be asserted at any point before or after the assertion of SYSCOREQ. However, it is required to be asserted to guarantee the corresponding assertion of SYSCOACK. When AWAKEUP is asserted with SYSCOREQ asserted and SYSCOACK deasserted, it must remain asserted until SYSCOACK is asserted. — It is permitted for AWAKEUP to be asserted at any point before or after the deassertion of SYSCOREQ. However, it is required to be asserted to guarantee the corresponding deassertion of SYSCOACK. When AWAKEUP is asserted with SYSCOREQ deasserted and SYSCOACK asserted, it must remain asserted until SYSCOACK is deasserted.
• It is permitted, but not recommended, to assert AWAKEUP then deassert it without a transaction taking place.	允許但不建議，當沒有transaction發生時，dessert AWAKEUP信号。
Note There is no requirement relating to the assertion of AWAKEUP relative to WVALID. However, for components that can assert WVALID before AWVALID, the assertion of AWAKEUP at least one cycle before WVALID can prevent the acceptance of a new transaction being delayed.
If a slave has an AWAKEUP input, but the attached master does not have an AWAKEUP output, then either: • Tie AWAKEUP high, however this might prevent the slave interface from using low-power states. • Derive AWAKEUP from AxVALID and SYSCOREQ/ACK. This method enables the slave to use low-power states, but might introduce latency while the clock is enabled.

E2.9.2 ACWAKEUP rules and recommendations

The ACWAKEUP signal is only applicable to: • ACE5. • ACE5-LiteDVM. ACWAKEUP is an output signal from an interconnect interface and is asserted at the start of a snoop transaction to indicate that there is a transaction to be processed. This rule applies to either a normal coherency snoop transaction or a DVM snoop transaction:

• This specification recommends that ACWAKEUP is asserted at least one cycle before the assertion of ACVALID to prevent the acceptance of a new snoop transaction being delayed unnecessary. • ACWAKEUP must remain asserted until the associated ACVALID / ACREADY handshake to ensure progress of the snoop transaction. • After the ACVALID / ACREADY handshake, the master must remain active until the snoop transaction has completed. • It is permitted for ACWAKEUP to be asserted at any point before or after the assertion of ACVALID. • It is permitted, but not recommended, to assert ACWAKEUP and then deassert it without ACVALID being asserted.

ACWAKEUP是snoop channel使用的，用于interconnect喚醒master，根上面的AWAKEUP的使用差不多，提前發出，以免delay