GR740-UM-DS, Nov 2017, Version 1.7
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GR740
15.3.3 Byte enables and byte twisting (endianess)
The core has the capability of converting endianess between the two busses. This means that all byte
lanes can be swapped by the core as shown in figure below.
Table 263 defines the supported AHB address/size and PCI byte enable combinations.
As the AHB bus in the design is as big-endian, the core is able to define the PCI bus as little-endian
(as defined by the PCI Local Bus Specification) with endianess conversion or define the PCI bus as
big-endian without endianess conversion.
The endianess of the PCI bus is configured via the core specific Extended PCI Configuration Space.
15.3.4 PCI configuration cycles
Accesses to PCI Configuration Space are not altered by the endianess settings. The PCI Configuration
Space is always defined as little-endian (as specified in the PCI Local Bus Specification). This means
Table 263.
AHB address/size <=> PCI byte enable combinations.
AHB HSIZE
AHB ADDRES
S[1:0]
Little-endian CBE
[3:0]
Big-endian CBE
[3:0]
00 (8-bit)
00
1110
0111
00 (8-bit)
01
1101
1011
00 (8-bit)
10
1011
1101
00 (8-bit)
11
0111
1110
01 (16-bit)
00
1100
0011
01 (16-bit)
10
0011
1100
10 (32-bit)
00
0000
0000
Figure 18.
GRPCI2 byte twisting
PCI bus
AHB bus
31-24
23-16
15-8
7-0
31-24
23-16
15-8
7-0
GRPCI2
Address 3
Address 3
Address 0
Address 0