Dsp Data Format; Conversion Through The Dsp Mmu - Texas Instruments OMAP5910 Technical Reference Manual

Endianism Conversion

2.11.1 Conversion Through the DSP MMU

Table 2–71. DSP Data Format
2-72
Swapping buffers are implemented at the boundary between the DSP and the
DSP MMU (see Figure 2–24). Assuming that the OMAP5910 system memory
is organized in little endian mode, data from and to the DSP is converted as
follows:
-
Data is written from the DSP to the system memory.
In the DSP, data is organized in big endian mode (see Table 2–70), but the
bytes are swapped in order to recognize the data in little endian mode (see
Table 2–69).
-
Data is read from the system memory to the DSP.
In system memory, data is organized in little endian mode, but the bytes
are swapped in order to reorganize the data in big endian mode.
-
32-bit word is written from the DSP to the system memory, but beginning
at an odd address (for example, 0x000002) or with the bit byte_nword set
to 0.
In the DSP, the data is organized in DSP data format (see Table 2–71), but
the 16-bit words are swapped in order to reorganize the 32-bit data in little
endian mode.
-
32-bit word is read from the system memory to the DSP, but beginning at
an odd address (for example, 0x000002) or with the bit byte_nword set to
0.
In system memory, the data is organized in little endian mode, but the
16-bit words are swapped in order to reorganize the 32-bit data in the DSP
data format.
Note:
16-bit word and single byte accesses are always right justified. The swap-
ping logic is power-up disabled.
DSP Data Format (32-Bit Word Access—
Odd Address or Enabled byte_nword Option)
31 24 23
Word
Byte 1
CC
16 15
Byte 0 Byte 3
DD AA
8 7 0
Word 1
Byte 2
BB