The Plug & Play Association was established to help companies integrating products bought on the OEM market and the naive computer user navigate the swamps of DIP switches, configuration systems, IRQs and resource conflicts that affect the multitude of add-in boards. However, it is letting a golden opportunity to clear up the confusion slip by and handing architectural control over to Microsoft Corp. More than ever before, computilliterate people are purchasing computers and then wanting to expand functionality with extra boards and boards, such as adding facsimile, sound and CD-ROM capabilities. These boards interact with the system software and application programs through interrupts, input-output ports, memory and direct memory access channels. Some resources, such as interrupts, can be shared by add-in boards, though only if the device drivers were designed to share interrupts, if they were not they need their own dedicated interrupts, ports and so on, while memory windows cannot be shared.
Patience and pain
Uninstallable or difficult add-in boards and boards are pushing up the cost of ownership for the user and support costs for personal computer and peripheral manufacturers, as they have to guide customers through the installation. Corporate computer divisions can spend as much money on the installation of the upgrades as on the hardware itself. The new computer users want to be ‘future proofed’, able to upgrade as needs demand and as new capabilities become available and to do this easily. They will not tolerate an error-prone system configuration process and will return boards that do not configure quickly and easily. Indeed, CompUSA Inc, the personal computer retailer, revealed recently that 25% of multimedia kits sold today are returned due to installation difficulties. Many of the buyers of the other 75% will have managed installation only with patience and pain. These multimedia boards support multiple functions, each requiring system resources. To make configuration more likely, boards offer a number of alternative configurations of resources. This can complicate the matter further for the consumer as they work out which configuration will work, with the add-ins already present. The AT was set up to facilitate the job of installation but was rapidly swamped by the proliferation of boards, requiring installers to understand terminology and know all the resources currently used by existing boards and needed by new boards, to manage configuration. Arise the white knight of the Plug & Play Association. Plug & Play will make the computer do the work – a nirvana to the confused and frustrated consumer. Its architecture comprises a BIOS, a Configuration Manager, an AT Configuration Utility and an Embedded System Configuration Database. The BIOS detects and configures add-in boards as part of the boot process and provides run-time services to enable system software to co-ordinate configuration management with the BIOS.
By David Johnson
The Configuration Manager completes the auto-configuration of Peripheral Component Interconnect and AT boards, configuring those boards not already configured by the BIOS. It also provides other device drivers with access to configuration information for all devices in the system. The AT Configuration Utility enables users to choose conflict-free configurations for non-plug and play AT add-in boards, capturing configuration information and writing it to the Embedded System Configuration Database and from this the Configuration Manager and BIOS identifies available system resources for the boards. The database stores information for the current devices in the system on the system board and add-in boards and requires an in-system updatable non-volatile memory of 4Kb. This is normally Flash memory as Electrically Erasable Programmable ROM is expensive and add an additional component requirement to the system. The Flash used for the plug and play BIOS and Embedded System Configuration Database storage is predominantly Intel Corp’s Boot Block Flash, and hence Intel supports the program
me and offers two development kits for OEM customers and BIOS vendors to encourage developers to embrace the standard. Flash provides greater inventory flexibility, enabling in-system BIOS code programming at the assembly line level plus just-in-time configuration of systems in inventory. Also Flash BIOS can be updated by floppy disk or bulletin board, rather than requiring computers to be returned to the dealer or manufacturer for service. The main BIOS code is also backed up by the hardware-lockable Boot Block, containing sufficient code to restore the system if the main BIOS is erased during an update. The Boot Block also contains two Parameter Blocks for storing files that only occasionally need to be updated occasionally, one of these can be used in plug and play for updatable Embedded System Configuration Database storage, the other used by the OEM to store manufacturing data, verification data or local language codes. The Main Block is used to store the system BIOS including device drivers, power management, video graphics, Peripheral Component Interconnect and plug and play. On booting up, the BIOS identifies boards to be configured and checks the database to see if any boards have been added. If so, any resource conflicts are resolved, a new register generated and saved for the future boots. So how does a vendor go about embracing plug and play?
Racing cars
The glossy from Intel promises that users can ensure that new systems will provide Plug and Play auto-configuration technology by looking for systems that are Plug and Play ready. This is the crucial problem facing the buyer. There is no easy way to look for systems that are Plug & Play ready, no industry standard defined to adhere to, no logo from the Plug & Play Association and no intention of bringing one out. Buyers will have to await the launch of Windows95, whenever that eventually happens, to have a logo that demands plug and play hardware. However Windows95 demands other criteria from people building the hardware that have nothing to do with Plug & Play, and hence those system builders that do not fulfil all the criteria, but are Plug & Play, will still not be Plug & Play by implication. The Association is handing the future of the standard into the capable hands of Microsoft and forcing manufacturers to dance to Microsoft’s tune. In the mean time, the Plug & Play Association suggests board and personal computer buyers pore over specification sheets looking for promises of Plug & Play, and returning boards or boards that cause problems so shops will build up danger lists. The reason for not making a logo – a fear that personal computers will end up looking like racing cars!
