Serial Switch Control Panel (IIfx Serial Switch cdev)
If an application requires direct access to the SCC serial chip, then you should license the Serial Switch control panel from Apple Software Licensing. The native mode of the IIfx uses a special processor to handle all SCC work, thus increasing overall machine performance by offloading this task from the CPU. However, applications must sacrifice direct SCC access for this performance gain. The Serial Switch control panel allows applications which must directly access the SCC to bypass the processor while sacrificing the increased performance.
This control panel sets a bit in parameter RAM which the IIfx checks during startup. If “Faster” mode is chosen (default), then the IIfx uses the special processor, but if “Compatibility” mode is chosen, then the IIfx lets the CPU handle SCC processing, which allows direct access. To license this control panel, contact:
Software Licensing Department
Apple Computer, Inc.
2420 Ridgepoint Drive, MS: 198-SWL
Austin, TX 78754
Telephone: 512-919-2645
AppleLink: SW.LICENSE
Internet: SW.LICENSE@applelink.apple.com
Note that purchasers of the Mac OS Software Developer’s Kit have the right to distribute the Serial Switch control panel pursuant to the terms of the license included with the Mac OS Software Developer’s Kit.
There is no way for an application to determine in which mode it is running; therefore, if the machine is in “Faster” mode and an application attempts a direct call to the SCC, the machine crashes.