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Use of a CAM for Bus Allocation

IP.com Disclosure Number: IPCOM000034515D
Original Publication Date: 1989-Mar-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Calvignac, J: AUTHOR [+2]

Abstract

This article describes the use of a CAM (Content Addressable Memory) for the attribution of allocated slots of a TDM (Time Division Multiplexed) bus to the users which are sharing this bus. The figure shows several communication adapters with limited throughput connected to a plurality of users and sharing a common bus having a high throughput. It is assumed that the TDM bus is carrying 2048 slots in a 125- microsecond period, and the adapters which are connected to it can each handle only 128 slots in the same 125 microseconds. The connection of the user of an adapter to a slot of the bus, is made by the micro-code running in the adapter which writes information in tables located in every adapter, in order to allow the adapter to know if a slot coming on the bus is allocated to one of its own user.

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Use of a CAM for Bus Allocation

This article describes the use of a CAM (Content Addressable Memory) for the attribution of allocated slots of a TDM (Time Division Multiplexed) bus to the users which are sharing this bus. The figure shows several communication adapters with limited throughput connected to a plurality of users and sharing a common bus having a high throughput. It is assumed that the TDM bus is carrying 2048 slots in a 125- microsecond period, and the adapters which are connected to it can each handle only 128 slots in the same 125 microseconds. The connection of the user of an adapter to a slot of the bus, is made by the micro-code running in the adapter which writes information in tables located in every adapter, in order to allow the adapter to know if a slot coming on the bus is allocated to one of its own user. For every slot coming on the bus (i.e., at every bus cycle (30 or 60 ns)), a given adapter has to fetch in its table, the following information: 1.If the bus slot is allocated to one of its own users, and 2.If yes, which user, among the 128, can handle it. The table is built in a content addressable memory wherein each word is associated with one user of the adapter. (There are as many words in the CAM as there are users connected to the adapters.) When a user has to be connected to a bus slot, the slot "Ti" is written in the CAM at the address corresponding to this user, with an additional bit in order to tell the allocation that it is...