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MMU_400 - transaction labels

Incoming transactions need labels, made up of a StreamId and an SSD_Index or SSD (Security State Determinator).

The SSD_Index/SSD, StreamId pair maps a transaction to a security world (Secure or Non-secure) and a translation context that holds the information necessary to perform the translation. Transactions with the same label appear the same.

You use SSD_Index to indirectly find the security world of the transaction using a mapping table (SMMU_SSDRn) in the SMMU, while SSD directly encodes the security state of the transaction.

Note

The security state of the transaction is independent of the Normal/Secure attribute of the transaction.

In the case of the MMU-400, the secure transactions never go to a translation context and instead can either be faulted, or bypass the address translation and have a limited attribute-only transformation applied.

In a hardware System on a Chip (SoC), the StreamId and the SSD_Index are usually formed by side-band signals on the bus or by AXI routing IDs, for example. Models do not have direct parallels for these signals. Instead, you must label transactions coming from a device.

The MMU_400 component uses the top 16 bits of the 32 bit master_id as a label. It has parameters such as:

label0_read_stream_id label0_read_ssd label0_write_stream_id label0_write_ssd ...

These map a label N (range 0..31) in the top 16 bits of the master_id to a particular StreamId and SSD_Index/SSD.

Note

The read and write transactions can have different StreamIds and SSD_Index/SSDs.

If MMU_400 uses SSD_Index es, then the parameter label{N}_{read/write}_ssd is the index. Otherwise it is 0 or 1, for Secure and Non-secure, respectively.

Transactions have a master_id field, set by a master. Many masters simply use zero, and these often do not allow you to change it. A simple Labeller component exists to put the labels in the master_id. Place it under each upstream device or bus-segment that the SoC wishes to distinguish. The LISA code shows you how it works, so you can create alternative labeling components.

The MMU_400 component is a wrapper round the component MMU_400_BASE. If the SoC identifies transactions in an alternative way, then you can write a new wrapper for MMU_400_BASE and implement your own identification scheme. The LISA code shows you how it works. In particular, you must replace the identify behavior with one specific to the SoC.

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