7.8.4. Operation example

Figure 7.10 shows a possible sequence of events of the ports on the Trace Funnel and the multiplexor selection. This example also assumes the only four trace sources are connected and that the priority encoding follows the reset/default priority, highest priority to slave port 0, lowest to slave port 3. The Minimum HoldTime Register is set-up to hold sources for two cycles before changing to a higher priority source.

Up to time marker t0 the lowest priority source is selected, slave port 3, because it always has data ready to be emitted. The trace sink, connected to the Trace Funnel master port, is stalling and so slowing the draining of the trace sources.

At point t0, a higher priority source indicates valid data is available, ATVALIDS2 goes HIGH, so the arbitration unit selects slave 2 because the minimum hold time for slave 3 is achieved.

At point t1, slave 1 asserts ATVALIDS1 and no higher priority sources indicate valid data so the arbiter switches to slave 1. Even though slave 2 has valid data, the arbiter unit switches to slave 1 because the minimum hold time for slave 2 is already achieved.

At point t2, slave 0 asserts ATVALIDS0 indicating valid data. Because the minimum hold time is not achieved by slave 1 at this point, the arbiter unit does not switch to slave port 0.

At point t3, the arbiter unit switches to slave port 0 even though slave port 1 has valid data because the minimum hold time is achieved by slave port 1.At point t4, the arbiter unit switches to slave port 1 because the slave port 0 deasserts ATVALIDS0.

At point t5, the arbiter unit switches back to slave port 2 because the slave port 1 deasserts ATVALIDS1.

Figure 7.10. Example operation with four trace sources

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