October 90 - Macintosh Q&A
Macintosh Q & A
MACINTOSH DEVELOPER TECHNICAL SUPPORT
QI am confused about the service routines and data areas passed in the _ADBOp call. What does it all mean?
A That 's a good question. The ADBOp call looks like this:
FUNCTION ADBOp (data:Ptr; compRout:ProcPtr; buffer:Ptr;
commandNum:INTEGER) : oserr;
data is a pointer to the "optional data area." This area is provided for the use of the service routine
compRout is a pointer to the completion or service routine to be called when the _ADBOp
command has been completed. It has the same meaning as the service routine passed to the
buffer is a pointer to a Pascal string, which may contain 0 to 8 bytes of information. These are the 2
to 8 bytes that a particular register of an ADB device is capable of sending and receiving.
commandNum is an integer that describes the command to be sent over the bus.
There is some confusion over the way the completion routines are called from _ADBOp. You can
call these routines in one of three ways, depending on what you want to do:If you do not wish to have a completion routine called, as in a Listen command, pass a NIL pointer
If you wish to call the routine already in use by the system for that address (as installed by
_SetADBInfo), call _GetADBInfo before calling _ADBOp, and pass the routine pointer returned by
_GetADBInfo to _ADBOp.
If you wish to provide your own completion routine and data area for the _ADBOp call, simply pass
your own pointers to the _ADBOp call.
Remember, there should rarely be a reason to call _ADBOp. Most cases are handled by the system's
polling and service request mechanism. In the cases where you must call _ADBOp, don't do it in a
polling fashion, but as a mechanism for telling the device something (for example, telling the device
to change modes or, in the case of the extended keyboard, to turn an LED on or off).
QThe AppleTalk spec claims a data rate of 230.4 kbaud, which should require a 3.6864 MHz input to the
SCC, but RTxCB on the Macintosh carries a 3.672 MHz clock. How does the AppleTalk driver reconcile this
discrepancy and what frequency should I use?
A The SCC contains a phase-locked loop that can lock on and synchronize with AppleTalk
transmissions whose clock rates are not exactly to specifications, so everything is fine as long as both ends of the
communication are using approximately the same clock frequency. If you are designing your own
AppleTalk hardware from scratch, it's easiest to use a 3.6864 MHz oscillator and a Z8530. This has
been tested and works just fine.
QWhen I fill in the fields of MPW's Name Binding Protocol (NBP) EntityName structure, AppleTalk doesn't
recognize the entity, even though I know it's out there. What's going on?
A The real definition of EntityName is three PACKED strings of any length (32 is just an example).
No offsets for Asm are specified since each string address must be calculated by adding the length
byte to the last string ptr. In Pascal, string(32) will be 34 bytes long (fields never start on an odd byte
unless they are only 1 byte long). So correct-looking interfaces for Pascal and C will be generated,
but they won't be the same, which is OK since they aren't used.
The point here is that you should never try to access the fields of the EntityName field directly. The
only reason the type is defined at all is so that you can allocate EntityName variables that will hold
the largest possible EntityName. To fill in an EntityName record, you should call the NBPSetEntity
routine.QHow do I determine which language is in use on the system?
A Every language has a corresponding KCHR resource. Inside Macintosh, volume I, page 499, lists the
currently defined country codes, which are the resource IDs of the KCHR resources.
To find out which KCHR is in use, call the Script Manager function GetScript with the verb
smScriptKeys. This call returns the ID of the KCHR resource in use (not the ID of the KEYC
resource, as stated in Inside Macintosh, volume V, page 312).
Here's a bit of C code that determines which KCHR is being used:
kchrID = GetScript(smRoman, smScriptKeys);
kchrID will be 1 when booted in French, 2 when booted in British English, and so on.
QWhen I use DeleteRevision to remove old revisions from my Projector database, the actual size of the
ProjectorDB file doesn't decrease much. How can I make the file smaller?
A Projector does not currently compact files. What it does is mark the areas of the database that are
now free and put them into a free page list. This effectively puts holes into your database, holes that
are subsequently filled up when you add more revisions.
Your database will get smaller only if the free pages are at the end of the file; then Projector will
shrink the file. However, there is very little you can do about controlling this situation. If you
absolutely must have a smaller database, then all you can do is check everything out, orphan the files,
and create a new database. The disadvantage of this method is that you lose all your revisions and
The Projector team is aware of the need to compact the database. The team is currently studying the
feasibility of adding such a function.
QHow does MultiFinder decide the starting order when you set multiple applications to start up under
MultiFinder with Set Startup? Is there any way to control the order?
A Here's the lowdown on MultiFinder application startup procedures.
From the Finder, launch, in order, application A, application B, and then application C. Switch to
the Finder, choose Set Startup, and select Open Applications and DAs. The launch order is now
application C, then application B, then application A.
Regardless of the type of view from the Finder, the startup order is from top to bottom, respectively.
If you'rereally interested, the Finder Startup file in the System Folder contains the applications and
files to be launched and the order in which they should be launched. This file contains a 'fndr' ID = 0
resource that stores the applications and their pathnames. The applications are launched in the order
in which they are listed. You can use ResEdit to view the resource and see the filenames, the
VRefNums, and the volume names of the startup applications. You can also tell the number of startup
applications by the number at the beginning of the resource (that is, 0000 0001 means one item).
Remember, however, that this informmation is valid only for pre-System 7.0 MultiFinder