> It takes 1000 microseconds to read /proc/rtc, whereas gettimeofday()
> takes only 15 microseconds to complete. Both of these are way too
> long. On my 133 Mhz 486, it seems like there should be a fine grained
> timer that takes less than 1 microsecond to read... any suggestions?
>
> -Truxton
>
How would you get a system call from user mode to take less than 1
microsecond, is really what you are asking. If you look at an Intel
book on your processor, you will probably find that you are asking a
bit too much because a protected mode Operating System does not
execute user-mode code. Instead, it switches to kernel mode to process
a function on behalf of the user. In so doing, it performs a complete
context-switch. It has to perform two, to complete the operation (it
has to get back from kernel mode). So, if reading the time took zero
seconds, I feel you are still in a world of hurt. There is also no
guarantee that the kernel will directly return to your process. There
may be higher-priority tasks and interrupts that must be handled
before your code gets the CPU back.
If you need such instant response, you probably need to put your
"realtime" code in a dummy "driver" and use insmod to insert into
the kernel. You could tell your driver to "do something" and return
results, either through /dev/your_device, or /proc/your_proc.
Cheers,
Dick Johnson
***** FILE SYSTEM MODIFIED *****
Penguin : Linux version 2.1.108 on an i586 machine (66.15 BogoMips).
Warning : It's hard to remain at the trailing edge of technology.
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