2.1.2 LPD-Q operating in sequencer mode

If the SEQUENCER parameter is set to one, then the LPD-Q operates in sequencer mode.

In sequencer mode, when the LPD-Q receives a quiescent entry or exit request on the control Q-Channel, it then sequentially sends the request to all the device Q-Channels. The LPD-Q waits for the response from each device before sending a quiescence request to the next device. The LPD-Q waits for all devices to respond before generating the response to the controller.

The following figure shows the LPD-Q configured as a sequencer.

Figure 2-2 Example LPD-Q sequencer connections
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Quiescence entry sequence

When the controller issues a quiescence entry request by asserting ctrl_qreqn_i, the LPD-Q sends a quiescence entry request on the highest device Q-Channel, dev_qreqn_o<NUM_QCHL−1>. If the device accepts the request by setting dev_qacceptn_i<NUM_QCHL−1> LOW, the LPD-Q decrements the device number and then sends a quiescence entry request to the next device. The LPD-Q repeats this process until all Q-Channels are quiescent or a denial occurs. The LPD-Q only sends an accept response to the controller, by asserting ctrl_qacceptn_o, when all devices accept the quiescence entry requests.

If any device denies the quiescence entry request by asserting dev_qdeny_i<X>, or asserts dev_qactive_i<X> when ACTIVE_DENY=1, then the LPD-Q asserts the ctrl_qdeny_o output. The LPD-Q does not send the remaining entry requests to Q-Channels that are in the Q_RUN state. If the quiescence entry request sequence was interrupted due to the assertion of:

dev_qdeny_i<X>

The LPD-Q returns channels to the Q_RUN state in ascending numerical order, from the device that asserted dev_qdeny_i<X> to device [NUM_QCHL−1].

dev_qactive_i<X>

The LPD-Q returns channels to the Q_RUN state, starting with the last channel to enter the Q_STOPPED state, followed by the channels in ascending numerical order, from the last device that accepted to device [NUM_QCHL−1].

When a dev_qactive_i<x> asserts, the LPD-Q waits until the device Q-Channel to which it is currently requesting quiescence accepts or denies the request, before it returns it to the running state. The point at which this channel returns to Q_RUN might not be in sequence with the other channels.

The LPD-Q only deasserts ctrl_qdeny_o, when all device channels return to the Q_RUN state and the controller sets ctrl_qreqn_i HIGH.

Quiescence exit sequence

When the controller issues a quiescence exit request, by deasserting ctrl_qreqn_i, the LPD-Q sends exit requests in a sequential sequence from device[0] to device[NUM_QCHL−1].

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