The Programmer's Guide to TRSDOS Version 6 - Tim Mann's Home ...

8. APPENDIX
8.1 BOOT INITIALIZATION ICNFG INTERFACING
In order to bring up the "DOS Ready" message when first powering up your computer, all
that you need do is place a SYSTEM diskette into the disk drive physically assigned to
the zero slot and depress a RESET button. In a few short moments, the ready prompt
appears on the display screen. Although, to the casual observer, not much appears to have
taken place, the machine has executed many "behind-the-scenes" procedures in order to
make the operating system available for your commands. The appendix section on SYSTEM
DISK BOOTING covers the individual steps undertaken. Here we discuss one of the final
steps - the execution of an initialization configuration routine.
Certain items of hardware require an initialization process before they can be used. For
instance, the RS-232 hardware needs to have parameters such as baud rate, word length,
and number of stop bits initialized before it can be used. This initialization process
could be a software routine which transfers the required parameters to the UART and Baud
Rate Generator. Certain hard disk controllers (the XEBEC controller, for instance) may
also need to be initialized before the attached disk drive can be used. This
initialization process may be implemented as a program executing under the AUTO command
or it may be a small routine that is part of the disk driver. If the latter, it would be
useful to have it execute prior to the "DOS Ready" message. You may also develop a
complex system function that takes over one or more SuperVisor Call functions. Since such
a function could reside in memory as part of a configuration, it would be useful to
have it automatically hook into the SVC table. Again, if the interfacing routine were
part of the function code in memory and the system provided a method to execute such a
routine, it would alleviate the problem of executing the hook.
After the system booting process loads a configuration file, it CALLs a vector, called
the @ICNFG vector. The contents of the vector are accessible from the FLAGS pointer
returned by the @FLAGS$ SuperVisor Call. Thus, any initialization routine that is part of
a memory configuration can be executed if its entry address is made available to @ICNFG.
This is accomplished by placing your entry address into @ICNFG while you save the former
address - eventually transferring control to the former address when your routine
completes its execution. This process is called "chaining into @ICNFG". If you need to
configure your own routine that requires initialization when the machine is booted, you
chain into @ICNFG.
Let's first look at a sample initialization configuration routine linkage. Your
initialization routine would obviously be unique to the function it was to perform so we
will not illustrate that part. A template for such a routine would appear as:
INIT CALL ROUTINE ;Start of init
LINK DB 'Roy' ;Pass to the chain
ROUTINE .
Your initialization routine
.
.
RET ;End with a RET instruction!
The relocated address identified by the label "INIT" is the entry point that will be
placed into the @ICNFG vector field. The 3-byte field identified as "LINK" will be used
to store the original contents of the @ICNFG vector field. Thus, when INIT receives
control, it "calls" your initialization routine then passes back to the next routine
chained into @ICNFG.
We will now illustrate a procedure to accomplish the chaining linkage. The chaining
procedure is performed by that part of your program which is going to place the memory-
8-1