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2.3. Operation

The MMU-500 routes each translation through the following logical processing steps:

  1. Security state determination.

  2. Context determination.

  3. Page table walk, if the translation is not cached in the TLB.

  4. Protection checks.

  5. Attribute generation or merging, depending on the programming.

You can configure the MMU-500 to bypass the transaction process for a transaction or to fault a transaction regardless of the translation state.

The primary function of the MMU-500 is to provide address and memory attribute translations, based on the address mapping and memory attribute information stored in translation tables.

The MMU-500 performs the following steps to achieve this:

  1. Receives an address transaction, along with security and stream information.

  2. Uses the security information received along with a transaction to determine additional processing steps for the transaction. The received security information is the security state of the originator of a transaction. The MMU-500 uses a Secure or Non-secure set of registers for additional processing of a transaction, depending on whether the security state of the originator is Secure or Non-secure, respectively. See Security determination.

  3. Uses the (S)CR0.CLIENTPD to determine whether stream matching is required. The transaction is bypassed if CLIENTPD is disabled.

  4. Uses the stream information received along with the transaction to determine the translation mechanism to apply to the transaction. The translation mechanism can be a bypass, a stage 1 translation, a stage 2 translation, or a stage 1 followed by stage 2 translation. See the ARM® System Memory Management Unit Architecture Specification.

  5. Adds the fault information to the Global Fault Status Register if a fault is identified in the translation process before a context is mapped. The MMU-500 adds the fault information to the Fault Status Register for the context bank, if a fault is identified after the context mapping.

    A fault results in an interrupt when interrupt reporting is enabled. You can clear interrupts by clearing the Fault Status Register.

    See the ARM® System Memory Management Unit Architecture Specification.

The MMU-500 supports both little and big endian translation tables. You can program endianness in the SMMU_CBn_SCTLR register. See the ARM® Architecture Reference Manual ARMv7-A and ARMv7-R edition.

For information about initialization and configuration, see Additional reading.

This section describes how the ARM® CoreLink™ MMU-500 System Memory Management Unit operates. It contains the following subsections: