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Technique for Storing Variable Length Data in a Circulating Buffer

IP.com Disclosure Number: IPCOM000046142D
Original Publication Date: 1983-Jun-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 3 page(s) / 53K

Publishing Venue

IBM

Related People

Eveland, RE: AUTHOR [+3]

Abstract

The present invention relates to utilization of a variable-length circular buffer to eliminate the need to break down long variable-length information into a plurality of small segments in order to store the data in the more traditional fixed-length buffer. In communicating text processing equipment using SNA (System Network Architecture) protocol, a Path Information Unit (PIU) trace facility is used by Customer Engineers in lieu of external line trace equipment to diagnose communication protocol and/or data compatibility related problems. In the conventional communications trace facility, every PIU received or transmitted is stored in a fixed-length circular PIU trace buffer. However, each PIU may be a variable length and therefore requires that header information be stored with the data to denote its length.

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Technique for Storing Variable Length Data in a Circulating Buffer

The present invention relates to utilization of a variable-length circular buffer to eliminate the need to break down long variable-length information into a plurality of small segments in order to store the data in the more traditional fixed- length buffer. In communicating text processing equipment using SNA (System Network Architecture) protocol, a Path Information Unit (PIU) trace facility is used by Customer Engineers in lieu of external line trace equipment to diagnose communication protocol and/or data compatibility related problems. In the conventional communications trace facility, every PIU received or transmitted is stored in a fixed-length circular PIU trace buffer. However, each PIU may be a variable length and therefore requires that header information be stored with the data to denote its length. A trace pointer is used to indicate where the next PIU should be stored in the buffer. In some embodiments, the PIU trace buffer is divided into N six-byte entries, each consisting of a header byte followed by five data bytes for PIU information. Since each entry in the trace table can trace only five bytes of PIU data, for a 256-byte long PIU, there will be 52 entries. Thus, there will be 52 header bytes. Also, if the PIU is not a multiple of five bytes in length, the last trace entry will contain 1-4 additional wasted bytes in the last trace entry. These wasted bytes reduce the number of data bytes that can be traced in a fixed-size PIU trace buffer. A significant amount of processor time is used for generating these headers, and system performance is affected.

Fox maximum use of the PIU trace buffer and for better system performance, we have come up with a scheme in which the PIU is not divided into five-byte entries. Using the two-byte header, a maximum of 1024 bytes of PIU can be traced. The header byte contains the following information: Byte 0 Bit 7 - Transmit/Receive Indicator

(0 = Transmit, l = Receive)

Bit 6 - Reserved

Bit 5 - Reserved

Bit 4 - Reserved

Bits 0-3 - PIU Trace Count Field

Byte l

Bits 0-7 - PIU Trace Count Field

The only fields relevant to this consideration are the short/long mode indicator and the count field.

The PIU trace buffer is treated as a 'circular buffer' such that the last byte is logically contiguous with the first. A two-byte Trace Pointer is provided to indicate the place in the PIU trace buffer where the data will be stored next. Also, another two-byte Dump Pointer is provided to indicate from where the valid data entry begins. When the last byte in the P...