Reasoning in signalling levels between Q Channel and P Channel in ARM Low Power Inteface

In the ARM AMBA Low Power Interface, the Q-Channel Handshaking signals are defined to have the logic such that at quiescence all the signals are low (QREQn, QACCEPTn, QDENY) while in the P Channel, the handshaking signals are all logic high. Why is this so?

  • Rephrasing the same question

    While the handshaking signals in the Q Channel (QREQn, QACCEPTn, QDENY) make all the signals in the interface to be low in the Quiescence state, the handshaking signals in the P Channel are all active high, such that each transaction starts and ends with a low state. In ARM’s protocol documentation, the explanation for either of the above has been provided as to result in better isolation states. How does one differ from the other and any possible reasoning behind such a design?

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