Intel NETWORK PROCESSOR IXP2800 - Manual (Page 57)

Hardware Reference Manual 57
Intel
®
IXP2800 Network Processor
Technical Description
2.6.1 Scratchpad Atomic Operations
In addition to normal reads and writes, the Scratchpad Memory supports the following atomic
operations. Microengines have specific instructions to do each atomic operation; the Intel XScale
®
microarchitecture uses aliased address regions to do atomic operations.
• bit set
• bit clear
• increment
• decrement
• add
• subtract
• swap
The Scratchpad Memory 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.
2.6.2 Ring Commands
The Scratchpad Memory provides sixteen Rings used for interprocess communication. The rings
provide two operations.
•
Get(ring, length)
•
Put(ring, length)
Ring
is the number of the ring (0 through 15) to get or put from, and
length
specifies the
number of 32-bit words to transfer. A logical view of one of the rings is shown in Table 9 .
Figure 9. Logical View of Rings
A9355-01
Head Count Size Tail
Full
1 of 16
Read / Write / Atomic
Addresses
Scratchpad RAM
Address
Decoder