[This answer was contributed by Pedro Zorzenon Neto.]
The functions usleep and nanosleep do not work for small intervals,
since the kernel [can] change to another task...
The solution comes out from I/O instructions.
Writing to I/O ports in ISA addresses will cause the system to wait for 1 microsecond
since
the ISA bus access time is 1 microsecond.
One I/O port that is never used
by the hardware in i386 machines is port 0x80.
So, writing one byte to I/O port 0x80 will result in a ``one
microsecond delay''.
This is not so accurate, but at least it will vary
less than 2% (my tests) from a Pentium 100 and a Athlon 850.
Some GNU/Linux low-level drivers also use this ``feature'' of writting
to port 0x80.
Attached is
the program
[and the header file]
that I used to do this (you can adapt it to
MS-DOS, I think the functions are inportb and outportb, but not sure).
In GNU/Linux you will need root permissions to write to I/O ports.
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