Browse Prior Art Database

Hardware Servicing of Data Buffer Depletion

IP.com Disclosure Number: IPCOM000109060D
Original Publication Date: 1992-Jul-01
Included in the Prior Art Database: 2005-Mar-23
Document File: 3 page(s) / 91K

Publishing Venue

IBM

Related People

Bellinghausen, JM: AUTHOR [+4]

Abstract

When receiving data from a communication line, the 3745 Network Control Program (NCP) allocates the limited memory based on past message lengths. When a message is received that requires more memory buffers than NCP has allocated, NCP buffer depletion results. As shown in Fig. 1, all traffic is passed through the Controller Bus Adapter (CBA), and it must continue to process messages from other Line Interface Modules (LIMs) while the Controller Bus Processor (CBP) microcode informs NCP to allocate more buffers for the current message.

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Hardware Servicing of Data Buffer Depletion

       When receiving data from a communication line, the 3745
Network Control Program (NCP) allocates the limited memory based on
past message lengths.  When a message is received that requires more
memory buffers than NCP has allocated, NCP buffer depletion results.
As shown in Fig. 1, all traffic is passed through the Controller Bus
Adapter (CBA), and it must continue to process messages from other
Line Interface Modules (LIMs) while the Controller Bus Processor
(CBP) microcode informs NCP to allocate more buffers for the current
message.

      Since the CBA can become the bottleneck for message processing,
it is imperative that the CBA hardware continue to service other LIM
messages while the CBP microcode and NCP allocate additional buffers
for a line with depleted buffers.  The hardware servicing of messages
with depleted buffers and the re-queuing and re-synchronizing of
those messages by the hardware and CBP microcode ensure the CBA can
continue to service messages from other communications lines without
impacting message throughput.  An external microprocessor could not
perform these operations with performance great enough to process
messages from all lines in an efficient manner.

      NCP uses a structure of LIM Programmed Status Areas (LPSAs),
chained to LIM Dynamic Programmed Status Areas (LDPSAs).  The LDPSAs
point to a series of free buffer pool chains for each communication
line in the receive direction (Fig. 2).  The Controller Bus Coupler
(CBC) processes all messages received from the LIMs into the format
understood by NCP.

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