7.3.2. CSTF Priority Control Register, 0x004

The CSTF Priority Control Register defines the order in which inputs are selected. Each 3-bit field represents a priority for each particular slave interface. Location 0 has the priority value for the first slave port. Location 1 is the priority value for the second slave port, Location 2 is the third, down to location 7, which has the priority value of the eighth slave port. Values represent the priority value for each port number. Figure 7.3 shows the bit assignments.

Figure 7.3. CSTF Priority Control Register bit assignments


Table 7.3 shows the bit assignments.

Table 7.3. CSTF Priority Control Register bit assignments

BitsField nameDescription
[31:24]-Reserved.
[23:21]PriPort 7Priority value of the eighth port. The value written into this location is the value that you want to assign the eighth slave port.
[20:18]PriPort 67th port priority value.
[17:15]PriPort 56th port priority value.
[14:12]PriPort 45th port priority value.
[11:9]PriPort 34th port priority value.
[8:6]PriPort 23rd port priority value.
[5:3]PriPort 12nd port priority value.
[2:0]PriPort 0Priority value of the first slave port. The value written into this location is the value that you want to assign the first slave port.

At reset the default configuration assigns priority 0 to port 0, and priority 1 to port 1.

If you want to give highest priority to a particular slave port, the corresponding port must be programmed with the lowest value. Typically this is likely to be a port that has more important data or that has a small FIFO and is therefore likely to overflow.

If you want to give lowest priority to a particular slave port, the corresponding slave port must be programmed with the highest value. Typically this is likely to be a device that has a large FIFO that is less likely to overflow or a source that has information that is of lower importance.

A port programmed with value 0 gets the highest priority. A port programmed with value 7 gets the lowest priority.Priority must always go to the highest priority source that has valid data available, if enabled. If a priority value has been entered for multiple different slave ports then the arbitration logic selects the lowest port number of them.

Note

This register must only be altered when the trace system is disabled, that is, trace sources are off and the system is drained.

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