7.8.6. Flushing example

Figure 7.11 has four sources connected to the first four slave ports and they are configured so that they are enabled with priorities reflecting their port number Slave port 0 is the highest priority, and port 3 is the lowest.

Before time t0, the system is under normal operation where different trace sources are selected according to the arbitration scheme, in this example slave port 2. At time t0 there is a request from the trace sink device to flush the system of historical data this request is then propagated onto the slave ports in the following cycle, at time t1. The CSTF, at this point, is then operating in a flushing mode where it selects each device that has not been drained in turn.

At time t1, CSTF selects slave port 1, highest priority with valid data, to drain first. At the same time the source connected to port 3 returns AFREADYS3, which causes AFVALIDS3 to be deasserted in the following cycle.

Draining of slave port 1 continues until time t2 where it responds with AFREADYS1. If all higher priority sources are already flushed, the CSTF then switches to the next highest priority source that is still to drain. In this example, slave port 2 is not selected. It is overridden because a higher priority port reports valid data that has not finished flushing, therefore slave port 0 is selected.

This continues until time t3 when AFREADYS0 goes HIGH and draining of slave port 2 can begin and which continues until time t4, AFREADYS2 going HIGH.

At time t4 all slave ports have responded with AFREADY HIGH. This indicates that there is no more historical information remaining at this level. This is indicated on AFREADYM with a HIGH response, that in turn results in AFVALIDM returning LOW. The flush sequence is now complete and the CSTF can return to normal operation, in this example by selecting slave port 1.

Slave port 1 is not selected for a second time before time t4 even though it is at a higher priority than slave port 2. This is because it has returned AFREADYS1 HIGH previously.

Figure 7.11. Flushing operation with four trace sources


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