Endianess Conversion - Texas Instruments OMAP5910 Reference Manual

DSP Subsystem Endianess
10.2

Endianess Conversion

198 DSP Subsystem
Endianess conversion is not always necessary. Conversion is required when
the following two conditions are met:
Shared data is accessed using different Endian formats. For example,
-
when the MPU core stores data in memory using Little-Endian format and
the DSP core reads the same data using Big-Endian data format.
Shared data is accessed using different access sizes. For example, when
-
the MPU core stores data using 32-bit accesses while the DSP core reads
the same data with 16-bit accesses.
The following statements can be made about endianess data formats and data
access size.
For shared data stored as a 32-bit element:
-
If this 32-bit element is accessed with one 32-bit access, then no
J
endianess conversion is required; this is independent of the
endianess of the accessing processor.
If this 32-bit element is accessed with two 16-bit accesses using a
J
different Endian format, then the two 16-bit halves within this 32-bit
element must be swapped.
If this 32-bit element is accessed with four 8-bit accesses using a
J
different Endian format, then the order of the four bytes within this
32-bit word must be reversed.
For shared data stored as a 16-bit element:
-
If this 16-bit element is accessed with one 16-bit access, then no
J
endianess conversion is required; this is independent of the
endianess of the accessing processor.
If this16-bit element is accessed with two 8-bit accesses using a
J
different Endian format, then the two bytes within this 16-bit element
must be swapped.
Table 86 shows the results of different accesses from a Big-Endian processor
to Little-Endian byte-addressable memory storing the 32-bit data element
0x1234 5678.
SPRU890A