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Memory folding technique for overcoming segmentation discontinuity Disclosure Number: IPCOM000033155D
Original Publication Date: 2004-Dec-25
Included in the Prior Art Database: 2004-Dec-25

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The following two distinct problems are to be solved: a) Segmentation is a common solution to guarantee efficient use of the available memory in network processing systems. This limited memory brings the problem of handling large frames or packets spreading across multiple segments. The possibility of data discontinuity leads to a scenario where part of the message-field is at one location and rest of the message-field at distant location (see example in Figure 1 below). b) Message-fields are often byte aligned, whereas protocol processors access data in 32, 48, 64, ... -bit words in one go. This leads to more complicated software that needs to cater for possible multiple positions of a message-field within the long word spreading across several bytes (see example in Figure 2 below). It is also possible that the required data field might not begin on a byte boundary. Up to now, there are five solutions as follows. a) Software handling of segmentation discontinuity and byte alignment: By noting the byte address, software decides which of the byte locations are to be accessed. In addition the software must constantly check for discontinuity. Disadvantage: lower performance and large code size. b) Byte access instruction: