DS508UM1
37
2.14
Endianness
The EP7312 uses a little endian configuration for internal registers. However, it is possible to connect the
device to a big endian external memory system. The big-endian / little-endian bit in the ARM720T control
register sets whether the EP7312 treats words in memory as being stored in big endian or little endian for-
mat. Memory is viewed as a linear collection of bytes numbered upwards from zero. Bytes 0 to 3 hold the
first stored word, bytes 4 to 7 the second, and so on. In the little endian scheme, the lowest numbered byte
in a word is considered to be the least significant byte of the word and the highest numbered byte is the
most significant. Byte 0 of the memory system should be connected to data lines 7 through 0 (D[7:0]) in
this scheme. In the big endian scheme the most significant byte of a word is stored at the lowest numbered
byte, and the least significant byte is stored at the highest numbered byte. Therefore, byte 0 of the memory
system should be connected to data lines 31 through 24 (D[31:24]). Load and store are the only instructions
affected by the Endianness.
Table 19 on page 38 and Table 20 on page 38 demonstrate the behavior of the EP7312 in big and little en-
dian mode, including the effect of performing non-aligned word accesses. The register definition section
of this specification defines the behavior of the internal EP7312 registers in the big endian mode in more
detail. For further information, refer to ARM Application Note 61, Big and Little Endian Byte Addressing.
CDENRX
CDENTX
CSINT
1 ms
1 ms
1 ms
Inte
rru
pt oc
curs
Inte
rr
u
pt oc
curs
Inte
rrup
t oc
curs
Figure 5. CODEC Interrupt Timing
Summary of Contents for EP7312
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