>>>>> "Momchil" == Momchil Velikov <velco@fadata.bg> writes:
>>>>> "Nagaraj" == Nagaraj <nagaraj@smartyantra.com> writes:
Momchil> FWIW, the problem is the classic producer-consumer problem with
Momchil> solutions described in _any_ OS textbook.
Momchil> Thus, the right solution would be to use semaphores. But, AFAIK,
Momchil> there are no semaphores shared between the userspace and the kernel.
Momchil> Probably futexes can do the work.
Alternatively (and better),
Have the driver allocate 2 buffers and mmap() them into the process.
Have the driver create 2 semaphores (initially zero) and let the app
post and wait on them with ioctls.
void *buf[2];
buf [0] = mmap (fd, ...);
buf [1] = buf [0] + HALF_BUFFER_SIZE; /* GCC extension :) */
no = 0;
while (!done ())
{
/* Let the driver know a buffer is available. DMA starts
if not started already. */
ioctl (fd, POSTSEM_0);
/* Wait until DMA interrupts and the interrupt handler signals the
semaphore. Driver continues filling the other buffer. */
ioctl (fd, WAITSEM_1);
/* Data is in buffer, no copying needed. */
do_stuff (buf [no]);
/* Switch buffers. */
no = !no;
}
One can add buffers to compensate for jitter. On a real-time OS two
buffers ought to be enough. Ok ?
~velco
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