User manual

Hardware Reference Manual 53
Intel
®
IXP2800 Network Processor
Technical Description
Each channel can be expanded by depth according to the number of port enables available. If
external decoding is used, then the number of SRAMs used is not limited by the number of port
enables generated by the SRAM controller.
Note: Doing external decoding may require external pipeline registers to account for the decode time,
depending on the desired frequency.
Maximum SRAM system sizes are shown in Table 11. Shaded entries require external decoding,
because they use more port enables than the SRAM controller can supply directly.
2.5.3 SRAM Atomic Operations
In addition to normal reads and writes, SRAM supports the following atomic operations.
Microengines have specific instructions to do each atomic operation; Intel XScale
®
microarchitecture uses aliased address regions to do atomic operations.
• bit set
• bit clear
• increment
• decrement
• add
• swap
The SRAM does read-modify-writes for the atomic operations, the pre-modified data can also be
returned if desired. The atomic operations operate on a single 32-bit word.
8M x 18 16 MB 21:0 23:22 3
16M x 18 32 MB 22:0 None 2
32M x 18 64 MB 23:0 None 2
Table 10. SRAM Controller Configurations (Sheet 2 of 2)
SRAM
Configuration
SRAM Size
Addresses Needed
to Index SRAM
Addresses Used
as Port Enables
Total Number of Port
Select Pairs Available
Table 11. Total Memory per Channel
SRAM Size
Number of SRAMs on Channel
12345678
512K x 18 1 MB 2 MB 3 MB
4 MB 5 MB 6 MB 7 MB 8 MB
1M x 18 2 MB 4 MB 6 MB 8 MB 10 MB 12 MB 14 MB 16 MB
2M x 18 4 MB 8 MB 12 MB 16 MB 20 MB 24 MB 28 MB 32 MB
4M x 18 8 MB 16 MB 24 MB 32 MB 64 MB NA NA NA
8M x 18 16 MB 32 MB 48 MB 64 MB NA NA NA NA
16M x 18 32 MB 64 MB NA NA NA NA NA NA
32M x 18 64 MB NA NA NA NA NA NA NA