Electrical computers and digital data processing systems: input/ – Intrasystem connection – Bus interface architecture
Reexamination Certificate
2000-01-31
2003-05-27
Auve, Glenn A. (Department: 2181)
Electrical computers and digital data processing systems: input/
Intrasystem connection
Bus interface architecture
C710S303000
Reexamination Certificate
active
06571308
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to computers and, more particularly, to computer bridge interfaces. A major objective of the present invention is to facilitate the development of accessories for the Handspring computer platform.
Much of modern progress is associated with the prevalence of computers, which are assuming an increasing variety of forms. Increasingly popular are hand-held computers that include software for helping people to organize information such as phone numbers, addresses, schedules, finances, etc. Such handheld computers are often referred to as “personal digital assistants” or “PDAs”. Provisions are made for adding software to provide for additional applications so that a user can extend the functionality of a PDA, while maintaining its familiar interface.
The most popular PDA recently has been the Palm Pilot available from 3com. The user interface is considered intuitive, and software development for the Palm Pilot has become an industry of its own. However, hardware expandability of the Palm Pilot is limited. This has contrained the development of applications that could benefit from the Palm Pilot interface, but require more or different processing capabilities that the “Dragonball” processor used by the Palm Pilot.
The Visor, available from Handspring, Incorporated, is similar to the Palm Pilot and shares its user interface and operating system. The Visor differs from the Palm Pilot since it includes a mechanism (the “Springboard Expansion Slot”) for hardware expansion. The specifications for this expansion slot have been published by Handspring to encourage the development of expansion modules to extend the capabilities of the Visor. The interface for the expansion slot is described in detail in the “Development Kit for Handspring Handheld Computers” available at the Handspring website www.handspring.com. In view of the publication of the interface specifications and active encouragement by Handspring to third party developers, it is likely that there will be intense Visor-compatible hardware development efforts.
While it is an important advance for devices with the Palm Pilot interface, the expansion slot has significant limitations. The logical bus interface for the Springboard expansion slot is a “slave”-only bus interface in which the Dragonball processor is the master and the expansion module is the slave. Basically, the Dragonball processor can initiate 16-bit reads and writes from and to the expansion module. Module-initiated communications are limited to a single interrupt. Additional control signals are provided to provide for hot-swapping (exchanging without powering down the PDA) expansion modules and for power management.
Buses that have higher-performance and that are more flexible than the Springboard expansion bus are well known. For example, multi-master master buses provide for parallel processing among different masters that communicate with each other and slave peripherals over the bus in a time-multiplexed manner. Many of these buses provide for variable wait states to provide flexible timing, while the Springboard expansion slot does not. A good example of such a multi-master bus is the Advanced System Bus or ASB that can be used with ARM7 processors for system-on-a-chip designs. The ASB and ARM7 specifications are available from Arm Limited, of the United Kingdom.
An ARM7 (more specifically, an ARM7TDMI) can be coupled to an ASB bus through an ARM7TDMI-to-ASB-Bus interface, available from Philips Electronics. The ASB bus can issue wait and grant signals that can affect the timing of data transfer requests originated by the ARM7 processor. These “handshaking” signals allow timing to vary on a per-transaction basis, which facilitates data transfers in an environment with a variety of peripherals with different timing requirements and/or multiple masters.
In contrast, the Springboard expansion bus does not provide for handshaking with the expansion module. Instead, transactions are “presumed” complete after a predetermined lapse of time. An expansion module can set this lapse of time upon insertion into the Springboard expansion slot. The expansion module must be designed so that all transactions are complete by the time the Visor presumes they are complete; otherwise, serious errors can result.
Associated with each bus is a specification that includes physical and logical protocols to which master and slave peripherals must conform. Typically, when a new bus is introduced, many peripherals are designed to be compatible with it. Some of these may be designed from the circuit level, while others may involve modifications of designs conforming to other bus standards.
If the bus is adopted for many applications, a library of peripheral design modules is often developed. This permits a modular approach to produce design, which greatly facilitates product development and reduces the time between conception and market entry. Such time-to-market advantages are critical in highly contested market areas, such as that expected for Handspring expansion modules.
The relatively simplicity of the Springboard expansion bus is certainly facilitates product development to a point. However, the functional limitations of the bus present a challenge, as the market demands more powerful expansion modules. What is needed is a system that provides for rapid development of powerful expansion modules for Springboard and similar expansion buses.
SUMMARY OF THE INVENTION
The present invention provides for a bridge between a host system and an external bus, where the host system includes a host processor and a host bus that provides an expansion interface. The host processor serves as the master of the host bus, and the external bus can serve as a part of a slave on the host bus. For example, a multi-master ASB bus can be bridged to the single-master Springboard bus of the Handspring Visor. In this case, the Visor's Dragonball processor is the master of the Springboard bus, and the combination of the bridge and the ASB bus is a slave. A user can thus be provided with the performance and flexibility of the ASB bus, while retaining the familiar, ergonomic interface associated with the Visor (and other Palm-compatible computers).
A developer for the relatively new Springboard platform can take advantage of the existing library of design modules available for the relatively mature ASB bus. Thus, the invention provides a rapid development platform for the competitive Springboard-compatible marketplace. Even where every function desired by the developer is not provided in the ASB library, the number of functions that must be met by designing new modules is greatly reduced by the present invention.
In general, to the extent that new module designs are required, they can take advantage of the features of the external bus. If the external bus is a multi-master bus, the new modules can function as masters on the multi-master bus and/or can take advantage of additional computing power made available by other masters on the multi-master bus.
A serendipitous additional advantage of the invention is that functional modules developed with the PDA platform in mind can have a bigger-than-intended market. For example, ASB bus peripherals developed for the Handspring Visor are then available as library modules for non-Springboard applications utilizing the ASB bus. Accordingly, the present invention allows development costs to be distributed over a larger-than-expected marketplace. Thus, the present invention can lower development costs attributable to the originally intended application. This advantage is in addition to the afore-mentioned advantages of more rapid development for the developer and more computing power to the user.
The present invention further provides that the bridge can include a translator between a host-bus protocol associated with the host (e.g., Springboard) bus protocol and a target-processor protocol associated with a target processor (e.g., the Arm7). In this case, the bridge further includes a processor-to-multi-master b
Reiss Loren B.
Sexton Bonnie C.
Shiel D. Adam
Koninklijke Philips Electronics , N.V.
Zawilski Peter
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