While the iMac is the first Macintosh system which does not provide an ADB port (excluding the PowerBook 145), we are providing an ADB/USB shim to support processes which make ADB Manager and Cursor Device Manager calls to control ADB devices. For example, such calls are often made to control extended keyboard LEDs and the cursor. It is important to understand that the shim will not support other types of ADB devices. The ADB/USB shim makes it possible for processes that expect an ADB keyboard and/or mouse to work seamlessly with the USB keyboard and mouse.
The ADB/USB shim is built into the "ROM in RAM" image on the iMac and will be included in the "ROM in RAM" image of future Power Macintosh systems which provide USB support. The ADB/USB shim is not included in the extension based USB components that one uses with the PCI USB cards. On an iMac, this means that one can make ADB Manager and Cursor Device Manager calls to see available USB keyboards and USB relative positioning devices. However, for existing PCI Power Macs which use the OPTi or CMD PCI USB cards, the USB devices will not be reported in responses of calls to the ADB Manager.
Serial Port/USB Compatability
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In contrast to the ADB/USB shim, there is no universal Serial/USB shim as part of the first release of MacOS USB DDK. The expected use of such a shim would be to allow processes which uses the Communication Toolbox CRM calls to identify available serial ports, to make the standard Device Manager based, Serial Driver calls to open, configure and use a USB serial device seamlessly.
For the introduction of the iMac system, a USB Serial Class Driver will need to implement it's own Serial/USB shim. For a coming release of the MacOS USB DDK (following the iMac intro) we will provide a USB Comm Class Driver which will support most USB Comm class devices that implement the Abstract Control Model as per the "USB Class Definitions for Communications Devices" document. This Comm Class Driver will implement a Serial/USB shim as mentioned above, for each supported USB Comm Class device.
We have provided the USBSerialBox example in the DDK. This sample is a work in progress example that has been used to create a class module to support the US Robotics 56K Voice Faxmodem Pro. The SerialBox sample is a class driver which demonstrates how to register a driver entry in the device Unit Table, then to call the Communication ToolBox CRM to register the serial port. The driver stub is a shim to facilitate the handling of the classic Serial Driver calls between the USB serial hardware. In this sample, the shim and class module are implemented in the same source code.
For use on the iMac, you will need to implement a Serial/USB shim for your USB Serial device. Once we have finalized our Comm Class Driver, the Serial Shim will be standardized. However if the Comm Class Driver needs to be modified for a particular device, the Serial Shim will still be needed. We do not expect the Comm Class Driver or the standardized Serial Shim to be available until Fall '98.
IMPORTANT NOTE: The serial shim provided as part of the Serial Box sample is not intended nor does it support LocalTalk or other externally clocked processes from a USB Serial Device.
