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PCI ISOCHRONOUS CONTROLLER PERMITS DETERMINISTIC PCI APPLICATIONS

IP.com Disclosure Number: IPCOM000009537D
Original Publication Date: 1999-Sep-01
Included in the Prior Art Database: 2002-Aug-30
Document File: 3 page(s) / 146K

Publishing Venue

Motorola

Related People

Edoardo Campini: AUTHOR

Abstract

This paper describes how a PC1 can be aug- mented to provide isochronous transfers, thereby enabling the development of deterministic PC1 applications.

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Developments Technical 0 M MO7WROLA =

PCI ISOCHRONOUS CONTROLLER PERMITS

DETERMINISTIC PCI APPLICATIONS

by Edoardo Campini

isochronous circuit is mapped to the PC1 bus. It may have registers and memory that can be accessed over the PC1 bus. The purpose of these registers and memory is for configuration and control of the circuit. Implementations which also include the bus arbitration functions (bus arbitration built into con- trol circuit), could also take advantage of the hidden bus arbitration feature of PCI.

  A PC1 agent, which desires a portion of the isochronous bandwidth, is required to make a request to the isochronous control manager (usually the host processor). This is usually done at power- up, when the entire PC1 bus is discovered and ini- tialized. However, it is conceivable that this could be dynamicahy re-configured. After all of the PC1 agents have made their request known to the isochronous manager, it becomes the responsibility of the manager to configure and enable/disable all of the isochronous control circuits. Each circuit makes use of counters, which are synchronized to the PC1 bus clock, to determine when the associated agent is prohibited from being an initiator on the bus. An agent is prohibited from being an initiator on the bus during a time slot which has been reserved for an isochronous transfer for another initiator.

  There are two major cases to consider in under- standing the operation of the isochronous control circuit. One case is when a reserved agent is requesting the bus to begin an isochronous transfer while the bus is idle, and the other case includes the condition where the bus is busy. Both of these cases are explained in the following examples.

  Case 1: The bus is idle during a time slot that has been reserved for agent "A" to initiate an isochronous transfer. Another agent ("B") would like to acquire the bus for an asynchronous transfer. Agent "B" would request the bus as normal. However, its isochronous control circuit would detect that agent "B" is prohibited from requesting

Q Molomla. 1°C. 1999 216 September 1999

ABSTRACT

  This paper describes how a PC1 can be aug- mented to provide isochronous transfers, thereby enabling the development of deterministic PC1 applications.

PROBLEM WITH EXISTING PCI AND PCI DERIVATIVES

  All existing PC1 and PC1 derivative systems lack the ability to support isochronous transfers. This deficiency prevents PC1 (and PC1 derivatives) from being effective in real-time applications, which by definition, require determinism.

SOLUTION TO PROBLEMS

  An Isochronous Control circuit can be added to a PC1 backplane to augment the PC1 bus. This ch- cuit allows existing PC1 devices to function, as well as newer PC1 devices designed to take advantage of the isochronous feature. In other words, the pro- posed isochronous circuit does not obsolete existing PC1 devices.

METHOD FOR AUGMENTING P...