Endianism Conversion
2-71
MPU Subsystem
2.11 Endianism Conversion
Because the TI925T is operated in little endian mode and the DSP is operated
in big endian mode, shared data must be converted to their respective formats
before any processing is done. Table 2–69 and Table 2–70 illustrate the little
and big data formats, respectively. In each case, the data is a reference to the
little endian format.
There are two ways to share the data between the TI925T and the DSP:
-
Through the DSP MMU
-
Through the MPUI
Endianism conversion is implemented between these two modules and the
DSP. The hardware converts both program code and data from big endian to
little endian mode when writing to the system memory and from little endian
to big endian mode when reading back from the system memory for all the data
access sizes when the logic is enabled.
Endianism conversion is performed in hardware, so that the data swapping is
transparent to software (reduce software overhead to format the data).
A bypass path is also implemented. If this case is not covered, the swapping
logic can be disabled and the conversion handled by software.
Table 2–69. Little Endian Data Format
Little Endian Format (32-Bit Word Access)
31
24 23
16 1
8 7
0
Word 1
Word 0
Byte 3
Byte 2
Byte 1
Byte 0
AA
BB
CC
DD
Table 2–70. Big Endian Format
Big Endian Format (32-Bit Word Access)
31
24 23
16 15
8 7
0
Word 0
Word 1
Byte 0
Byte 1
Byte 2
Byte 3
DD
CC
BB
AA
