Hi Sylvain,
SL>  > program. Keep in mind, that during this time, any other
SL>  > program running
SL>  > in this "task" is suspended. When you exit the TSR, it
SL> i can't figure how other programs in this task are suspended until I exit
SL> the TSR. Say i'm downloading few files and decide to pop up a tsr
SL> calculator in the same task. Will the transfer continue to receives files
SL> normally? Or the transfer will be suspended?
Generally, the transfer will be suspended....
It might be easier to look at it this way. The "intel" 80??? are single
task processors. (Yes, all of them...) In a multitasking operating
system, the processer does one task "at a time". So how does it
multitask? Simple... The processor does one task for a few clocks
then switches to the next task, it does the next task for a few clocks
and switches to the next... and so on....  Task priorities determine
how much of a processors time each task gets in relation to the others.
(There is alot more to this, but that's the general gist of it)
In a TSR, when it's running, it has captured the processor time away
from the running program. It keeps this time until it releases the
processor back to the original program....
There always exceptions to this rule.... Dos's PRINT.EXE is a good
example. It captures the printer's hardware interupt and returns
to dos. Most of the time PRINT.EXE is dormant. The TSR does nothing
until the printer "hardware interupts" the computer letting it know
it has printed what it has in "it's" buffer and wants more data.
The processor stops to service the hardware interupt and PRINT.EXE
goes into action. It sends a bundle of bytes out of the printer port
filling the printer's buffer and returns control to whatever program
is running. This happens sooo fast that it usually doesn't bother
whatever program is running.
X00, BNU, and other fossils work the same way. It doesn't do anything
unless there is data coming in or going out of the serial port. The
serial port interupt tells the fossil when to work.
The problem with a TSR calulator is that is occupies the keyboard
and the screen while it's running. This could bump heads with
another program that reads/writes to the screen buffer or keyboard
buffer.
This doesn't even mention TSR's that can open files, and do other
dos funtions. Since dos, itself, is a single task operating system,
can't open a file while it's writing to std-output. (safely)
Dos itself has a byte used to indicate that it's in use. It's
called the "indos flag". This is one byte that is examined by
TSR's to know when it's safe to do a peticular thing and not
crash the operating system.....
If your looking at doing file tranfers while running another task,
you might look into a TSR zmodem. It doesn't have to affect the
screen, keyboard, or other time sensitive hardware. It could run
happily as a TSR.
Glen.
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