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The sides of each Bridge component communicate using a Q-Channel interface for power control.
The intra-bridge Q-Channel interface coordinates the powering down of the entire bridge by providing communication between the bridge sides. The power Q-Channel and external gating Q-Channel, on either side of the bridge, use the intra-bridge Q-Channel interface.
The intra-bridge Q-Channel interface also has an extra signal that indicates whether the quiescence request is from the power Q-Channel or the external gating Q-Channel. The bridge can deny a power Q-Channel quiescence request but it cannot deny an external gating Q-Channel quiescence request.
The Q-Channel implements the low-power interfaces that the AMBA® Low Power Interface Specification, Arm® Q-Channel and P-Channel Interfaces describes.