From: me AT here DOT com
Newsgroups: comp.os.msdos.programmer,comp.os.msdos,comp.os.msdos.djgpp,comp.os.msdos.misc
Subject: Re: Control timing
Date: 2 Nov 2001 23:53:11 GMT
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To: djgpp AT delorie DOT com
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In comp.os.msdos.programmer jeffchan <jeffkhc AT netvigator DOT com> wrote:
> Thanks, i re-allocate the jobs into main function and ISR. Now the ISR
> is doing as your mention.

> Actually, the input data is analog voice data. I need to control an
> capture card to read and store it into hard drive. Now i find that
> some strange sound like "tak" in my recorded file. It appears in each
> times i use fwrite() to put the data from buffer into a file. When i
> change the buffer size, the period of the "tak" is also changed.

> What's it caused by and any idea to solve it?

Once I did high speed acquisition from an 4 channel A/D, and ended 
up 2 ISR -- one was timer activated that latched in the data

timer_ISR:
   disable; 
   for (i = 0; i < 4; i++) { 
      latch_in_channel[i]; 
   }
   start_conversion;  
   enable; 
   iret; 

the other one was activated by the copmpletion signal (all were OR-d 
to one pin) then figured out the source, read and stored the data

A2D_completed: 
   disable; 
   read_intr_ID; 
   read_data; 
   store_data; 
   enable;
   iret;


I had 2 ISR because it took several milliseconds from start_conversion 
to the A2D_completed, and by using 2 ISR's in this way, I could 
make my ISRs as efficient as possible. 

  
As to check time spent in the ISR, you can read the 8254 timer 
directly, i.e.:

some_ISR:
  disable; 
  start_LSB = inportb(0x40); 
  start_MSB = inportb(0x40); 
  do_something; 
  end_LSB   = inportb(0x40); 
  end_MSB   = inportb(0x40); 
  enable; 
  iret; 


This reads the HW timer, so it is accurate to a couple of us
as long as your ISR takes less than 55 ms.    

If your ISR takes more than 55 ms to execute, then it's a 
bad ISR.


> On the other hand, i create the file's name be around 23
> characters(including extension). Of course under dos will cuts it out.
> Does any method let me use long file name?

> Jeff



> "Alexander Russell" <alexander DOT russell AT telus DOT com> wrote in message news:<UwMD7.63547$Og4 DOT 9393877 AT news0 DOT telusplanet DOT net>...
>> "jeffchan" <jeffkhc AT netvigator DOT com> wrote in message
>> news:bf50ce95 DOT 0110301711 DOT 78e48e58 AT posting DOT google DOT com...
>> > Hi,
>> >
>> > That's mean i must install DOS on my PC. Can i use windows startup
>> > disk booting up, to make an environment as dos? Is that still same as
>> > dos box in win9x?
>> >
>> > And if the new_timer(void) routine is too much coding, it can't finish
>> > the job when the next interrupt came expected. Do i need to set some
>> > interrupt masking flags?
>> >
>> > How do i check the timing spent of this interrupt service routine?
>> >
>> > Jeff
>> >
>> 
>> I generally make an interrupt service as SHORT and FAST as possible. Set a
>> flag, store a bit of data in a global structure. then the main program polls
>> the vars set by the interrupt and does any longer processing.
>> 
>> For example, the interrupt my just store data to a queue, then the main prog
>> process the data in the queue and write it to disk.
>> 
>> As for dos 7, I haven't tried that, but its likely ok.
>> 
>> >
>> > > > > AJR - I don't see an obvious problem. Are you running under DOS? If
>>  running
>> > > > > under a dos box in win9x the timing will not be exactly what you
>>  expect.
>> > > >
>> > > >       Let me know the reason.
>> > > >
>> > > Windows 9x grabs all the interrupts, and lets dos programms 'use' them
>>  at
>> > > random intervals.
>> > >
>> > > > --
>> > > >   Peace - The choice of the new generation.

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