Intel NETWORK PROCESSOR IXP2800 - Manual (Page 122)

122 Hardware Reference Manual
Intel
®
IXP2800 Network Processor
Intel XScale ® Core
16-Bit (Word) Read
When reading a word, the Intel XScale ® core generates the byte_enable that corresponds to the
proper byte lane as defined by the endianness setting. Figure 25 summarizes byte enable generation
for this mode.
The 4-to-1 multiplexer steers byte lane 0 or byte lane 2 into the byte 0 location of the read register
inside the Intel XScale ® core. The 2-to-1 multiplexer steers byte lane 1 or byte lane 3 into the
byte 1 location of the read register inside the Intel XScale ® core. The Intel XScale ® core does not
allow word access to an odd-byte address. Select signals for the multiplexer are generated based on
endian setting and ByteEnable generated by the Intel XScale
®
core, as defined in Figure 24 .
Table 46 summarizes byte-enable generation for this mode.
Figure 24. Byte Steering for Read and Byte-Enable Generation by the Intel XScale ® Core
A9694-03
0
1
0
1
2
3
0
1
0
1
0
1
0
1
BE0
BE1
BE2
BE3
X_BE[0]
X_BE[1]
X_BE[2]
X_BE[3]
Big Endian =0
Little Endian = 1
D[7:0]
M[7:0]
M[15:8]
M[23:16]
M[31:24]
S0
S1
X[7:0] Byte 0
X[31:24] Byte 3
X[23:16] Byte 2
X[15:8] Byte 1
D[15:8]
D[23:16]
D[31:24]
Intel XScale ® Core
Intel ® IXP2800
Core Gasket
Notes: For 32-bit Operation S0[3:0] = 0001; S1[1:0] = 01
Otherwise: S0[3:0] = X_BE[3:0]; S1[1:0] = X_BE[1:2]