Nonaligned Read Word Access - Texas Instruments OMAP5910 Technical Reference Manual

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Table of Contents

Figure 2–21. Nonaligned Read Word Access

Translation Fault

Domain Fault

Permission Fault

If the access generates an alignment fault, the access sequence aborts with-

out checking access rights.

If a nonaligned read access is executed and the alignment fault is disabled,

data is accessed at a word address and rotated inside the core as shown be-

low. If a nonaligned half-word or word write is executed while the alignment

fault is disabled, the write is done on a half-word or word address boundary.

Figure 2–21 is an example of read word access on byte 11.

There are two types of translation fault: section and page.

A section translation fault is generated if the level 1 descriptor is marked

as invalid. This happens if bits [1–0] of the descriptor are both 0.

A page translation fault is generated if the page table entry is marked as

invalid. This happens if bits [1–0] of the page table entry are both 0.

There are two types of domain faults: section and page. In both cases, the level

1 descriptor holds the 4-bit domain field that selects one of the sixteen 2-bit

domains in the domain access control register. The two bits of the specified

domain are then checked for access permissions, as detailed in Table 2.15.

In the case of a section, the domain is checked once the level 1 descriptor

is returned.

In the case of a page, the domain is checked once the page table entry is

A section or page domain fault occurs if the permission access is either no

access (00) or reserved (10).

There are two types of permission faults: section and subpage. Permission

fault is checked at the same time as the domain fault. If the 2-bit domain field

returns client (01), then the permission access check is invoked as follows:

Word address in memory

Word is rotated inside the MPU core

MPU Memory Management Unit

Read Access on Address Byte 11

MPU Subsystem