HIGH BANDWIDTH, HIGH CAPACITY LOOK-UP TABLE IMPLEMENTATION IN DYNAMIC RANDOM ACCESS MEMORY
Fixed-cycle latency accesses to a dynamic random access memory (DRAM) are designed for read and write operations in a packet processor. In one embodiment, the DRAM is partitioned to a number of banks, and the allocation of information to each bank to be stored in the DRAM is matched to the different types of information to be looked up. In one implementation, accesses to the banks can be interleaved, such that the access latencies of the banks can be overlapped through pipelining. Using this arrangement, near 100% bandwidth utilization may be achieved over a burst of read or write accesses.
1 . A packet processor receiving data packets each including a header of a plurality of fields, comprising:
a data bus;
a dynamic random access memory having a plurality of banks each receiving data from the data bus and providing results on the data bus, each bank storing a look-up table for resolving a field of the header of each data packet; and
a central processing unit receiving the data packets and in accordance with the fields of each data packet generating memory accesses to the banks of the dynamic random access memory.
2 . A packet processor as in claim 1 , wherein the banks of the memory are accessed in a predetermined sequence during packet processing.
3 . A packet processor as in claim 2 , wherein each access has a fixed latency.
4 . A packet processor as in claim 1 , wherein the look-up table is duplicated in two of the banks.
5 . A packet processor as in claim 1 , wherein the dynamic random access memory further comprises a controller which includes a scheduler, and wherein the scheduler selects and schedules the memory bank to access for each memory access received.
6 . A packet processor as in claim 5 , wherein the controller further comprises a finite state machine for effectuating the scheduler's selection and schedules.
7 . A packet processor as in claim 6 , wherein the scheduler inserts non-functional memory accesses to preserve an order of execution of the memory accesses.
8 . A method for processing a data packet, comprising:
providing a dynamic random access memory having a plurality of banks each receiving data from a data bus and providing results on the data bus;
storing in each bank a look-up table, each look-up table being provided to resolve a field of a header of the data packet; and
receiving the data packet and, in accordance with the fields of the data packet, generating memory accesses to banks of the the dynamic random access memory.
9 . A method as in claim 8 , wherein the memory accesses are generated in a manner such that the banks of the memory are accessed in a predetermined sequence.
10 . A method as in claim 9 , wherein each access has a fixed latency.
11 . A method as in claim 8 , further comprising duplicating one of the look-up tables in two of the banks.
12 . A method as in claim 8 , further comprising providing in the dynamic random access memory a controller which includes a scheduler, and wherein the scheduler selects and schedules the memory bank to access for each memory access received.
13 . A method as in claim 12 , further comprising providing in the controller a finite state machine for effectuating the scheduler's selection and schedules.
14 . A method as in claim 13 , wherein the scheduler inserts non-functional memory accesses to preserve an order of execution of the memory accesses.