2.3.1. StreamID

A StreamID maps the incoming transaction to a context by using the stream mapping table. The characteristics of the StreamID are as follows:

For more information about StreamID signals, see Sideband signals.

When the StreamID is configured as 1-10 bits

The StreamID width in the TCU is a constant 15 bits. The MMU-500 zero-extends each TBU StreamID to form a 10-bit field that it appends to the 5-bit TBU ID field, making the StreamID the required 15 bits wide by the time it reaches the TCU.

When the StreamID presented to each TBU is not unique

You must ensure that a unique ID is presented to the TCU, by appending the StreamID to the 5-bit TBU ID field as shown in Figure 2.5.

Figure 2.5. StreamID is not unique

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When the StreamID presented to each TBU is unique

If the StreamID presented to each TBU is already unique, and the TBU ID addition is not required, then you can use the SMR to mask the TBU ID if required, as shown in Figure 2.6.

Figure 2.6. StreamID is unique

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When the StreamID is configured as 15 bits

The StreamID widths in the TBU and the TCU are both 15 bits, meaning that the TBU ID is not appended.

For more information on StreamID-to-context mapping, see the ARM® System Memory Management Unit Architecture Specification.

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