Technical Note HW09

Macintosh IIfx: The Inside Story

CONTENTS What's Inside ADB CD-ROM Driver EtherTalk Driver (.ENET) MacsBug NuBus SADE MultiFinder SCC SCSI SWIM VIA2 Summary References Downloadables

This Technical Note addresses various areas of potential incompatibilities with the Macintosh IIfx and current software applications and provides information about some of Apple's compatibility software updates. [Feb 01 1991]

What's Inside

On the Macintosh IIfx, the CPU no longer handles I/O operations like floppy disk access, SCC access, and mouse events. Instead of the CPU doing all of the work, the IIfx contains a couple of separate I/O processors, Apple custom ASICs, to handle all floppy disk, mouse, and SCC I/O. With the advent of these new I/O processors (IOP), the IIfx can handle smooth cursor movement and time consuming disk operations simultaneously. These new IOPs are just an example of the new capability of this machine.

Each of the following sections talks about the changes and added functionality which makes life difficult for some types of applications. The IOPs in the IIfx cause some applications problems, and this Note shows why certain techniques no longer work and provides solutions to work around these incompatibilities where possible. A few additional sections provide information about updated System Software or peripheral software from Apple which the IIfx requires for operation.

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ADB

Applications which depend upon direct access to the ADB transceiver or its VIA registers do not work with the IIfx, because the IOP which now handles ADB is not available for direct access. As in the past, the hardware is subject to change, and applications which access it directly break when new hardware is introduced. There is no solution for applications which try to directly access the ADB hardware; these applications must now use the ADB Manager or they cannot run on the IIfx and future Macintosh models.

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CD-ROM Driver

To use the AppleCD SC with a Macintosh IIfx (and IIci), you must use version 3.0.1 or later of the Apple CD-ROM drivers. Earlier versions of this driver are incompatible with this hardware. You can obtain a copy of this driver from any authorized Apple dealer, the Developer CD Series, AppleLink (Developer Services: Macintosh Developer Technical Support: Peripheral Software), and the Apple FTP site on the Internet (Apple.COM under ~ftp/pub/dts/sw.license/).

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EtherTalk Driver (.ENET)

To use the Apple EtherTalk card with a Macintosh IIfx, you should use version 2.0.2 of the EtherTalk driver. Earlier versions of this driver do not perform as well with this hardware. You can obtain a copy of this driver from any authorized Apple dealer, the Developer CD Series, AppleLink (Developer Services: Macintosh Developer Technical Support: Peripheral Software), and the Apple FTP site on the Internet (Apple.COM under ~ftp/pub/dts/sw.license/).

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MacsBug

To use MacsBug with a Macintosh IIfx, you must use version 6.2. Earlier versions of MacsBug are incompatible with this hardware. You can obtain a copy of MacsBug 6.2 from APDA, the Developer CD Series, and AppleLink (Developer Services: Macintosh Developer Technical Support: Tools: MacsBug).

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NuBus

If the Macintosh IIfx executes a Read-Modify-Write NuBus(TM) code sequence to a card (i.e., TAS or test and set) and immediately follows it with a regular cycle Read or Write, the system hangs. The solution to this problem is to execute five NOP instructions between the TAS and the next cycle. This number of NOP instructions should also handle future accelerations of the CPU clock, should Apple decide to further accelerate it.

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SADE MultiFinder

To use SADE with a Macintosh IIfx, you must use version 6.1b9 of MultiFinder with the Set Aside feature. Earlier versions of MultiFinder are incompatible with SADE on this hardware. You can obtain a copy of MultiFinder 6.1b9 from APDA with SADE 1.1, the Developer CD Series, and AppleLink (Developer Services: Macintosh Developer Technical Support: Tools: SADE MultiFinder). Developers may not distribute MultiFinder 6.1bx to customers, even if licensed to distribute Apple's Macintosh System Software.

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SCC

Like the processor which controls floppy disk and ADB I/O, the IIfx has another ASIC to control the SCC, but unlike the former, this processor is capable of running in a special "IOP Bypass" mode which allows direct access to the SCC.

The new SCC architecture also contains a few other differences from the previous architecture. On the IIfx, there is no longer a VIA line available for monitoring the Wait/Request signal of the SCC. Applications which depend upon this bit have no solution to this problem and are incompatible with the IIfx. In addition, on the IIfx the vSync bit (which has been available since the Macintosh SE) has moved to a new location; however, Apple is providing developers with a trap call (_HWPriv) which allows applications to enable or disable this bit in its new location, thereby providing a solution for applications which depend upon this bit. For more information on this trap call, see the vSync Bit section later in this Note. Technical Note #261, Cache As Cache Can, also addresses _HWPriv.

IIfx Serial Switch cdev

If an application requires direct access to the SCC, then you should license the IIfx Serial Switch cdev 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 IIfx Serial Switch cdev allows applications which must directly access the SCC to bypass the processor while sacrificing the increased performance.

This cdev 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 cdev, contact:

Apple Software Licensing
Apple Computer, Inc.

20525 Mariani Avenue, M/S 38-I
Cupertino, CA 95014
(408) 974-4667
AppleLink: Sw.License
Internet: Sw.License@AppleLink.Apple.com

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.

Wait/Request Bit

On previous Macintosh models, there is a Wait/Request bit on the VIA1 register A for monitoring incoming serial data while the Macintosh is busy with some other operation. When the SCC receives a character, it sets this bit in the VIA, which tells the operating system that the SCC needs attention. Since the IIfx has a dedicated processor for SCC transactions, it has no need for this mechanism. Even if a machine is using the IOP Bypass mode to directly access the SCC, this line is not active, so applications which rely upon it are incompatible with the IIfx. For more information about this bit, refer to the Guide to the Macintosh Family Hardware, Second Edition.

vSync Bit

The _HWPriv ($A198, selector 7) routine enables or disables external SCC clocking. The external clock comes to the SCC through the RTxC signal, which is connected to the GPi pin on the serial port connector. This routine is used instead of writing directly to the vSync bit on VIA1 (which is not implemented on the IIfx), and it is backpatched into all previous CPUs, except the Macintosh Plus, which does not support external clocking. _HWPriv only works in IOP Bypass mode on the IIfx, and is documented below for your convenience:

Entry:
    d0.l = routine selector = 7
    a0.l =  <port number>.w <enable/disable ext clock>.w
            23-16: port number 0 = port A, 1 = port B,... for future expansion
            15-0 : 0 = internal clocking, 1 = external clocking
Exit:
    d0.l = zero if good, -1 if error
    a0.l = <port number>.w <last state of external clock>.w

Synchronous SCC I/O

If an application expects to make synchronous SCC I/O calls with interrupts turned off, it does not work on the IIfx, because the new IOP serial driver uses the Deferred Task Manager, which is interrupt driven. If an application tries to do something like communicate with the IOP SCC driver when interrupts are turned off, the IIfx hangs.

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SCSI

The Macintosh IIfx may cause developers problems in two areas which deal with the SCSI interface. The first are the SCSI low-memory globals. A few applications rely upon undocumented low-memory globals which point to addresses in the SCSI controller chip; however, on the Macintosh IIfx, these globals now point to an entirely different area. If an application depends upon these globals, it either does nothing or crashes on the IIfx. The second problem deals with SCSI termination. For more information about SCSI termination on the Macintosh IIfx and how it differs from previous Macintosh models, refer to Technical Note #273, SCSI Termination.

In addition, although the IIfx hardware has SCSI DMA capability, the Macintosh System Software does not yet take advantage of it. Apple recommends that you wait until the Macintosh System Software implements support for the IIfx SCSI DMA to use this hardware feature.

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SWIM

On the IIfx, the floppy disk controller, the SWIM, is not directly accessible; instead, the IIfx has a processor which handles all floppy drive access. This processor, an Apple custom ASIC, is not accessible to third-party developers. The I/O processing hardware is subject to change, and applications which attempt to access it directly are likely to break when new hardware is introduced.

Apple has always recommended against direct hardware access, but some applications do it anyway, and these applications now have problems with the new IIfx hardware. The most common reason these applications access the hardware directly is to move hidden information to and from the disk. As a partial solution to this problem, the IIfx includes a new version of the Sony driver which allows applications to make a control call to get raw data from the disk. For more information on this new driver and control call, refer to Technical Note #272, What Your Sony Drives For You.

Asynchronous Disk I/O

If an application expects to make asynchronous I/O calls to the Sony driver with interrupts turned off, it does not work on the IIfx, because the new IOP drivers are interrupt driven. If an application tries to do something like open a resource when interrupts are turned off, the IIfx hangs.

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VIA2

All of the functionality of VIA2 has been moved to other chips in Macintosh IIfx, so if an application depends on VIA2 registers, it must find a different way to get the information for which it is looking to be compatible with the IIfx.

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This is What Makes a "Wicked Fast" Macintosh

The basic message of this Note is that if developers directly access Macintosh hardware, their applications are likely to break on new hardware like the Macintosh IIfx. If an application is having compatibility problems with the IIfx, they are probably due to one of these documented changes, and this Note should help provide the necessary solutions where they are available. If an application is having compatibility problems with the IIfx and they are not related to one of these areas, then qualified developers should contact Developer Technical Support for help in tracking down the problem.

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References

Guide to the Macintosh Family Hardware, Second Edition

Inside Macintosh, Volume V, Compatibility Guidelines

Inside Macintosh, Volume V, Deferred Task Manager

Technical Note M.OV.Compatibility-- Compatibility Guidelines

Technical Note M.OV.Compatibility -- Compatibility: Why and How

Technical Note M.OV.GestaltSysenvirons -- _SysEnvirons: System 6.0 and Beyond

Technical Note M.HW.Cache -- Cache as Cache Can.

Technical Note M.DV.SonyDriver -- What Your Sony Drives For You.

Technical Note M.DV.SCSITermination -- SCSI Termination

NuBus is a trademark of Texas Instruments.

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Downloadables

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