On Tue, 5 Aug 2003, Gerd Knorr wrote:
>> Using multiple mmap buffers, yes, but where's the point?
>Let video application and capture hardware work in parallel:
Ah, but since it works in parallel with just one mmap buffer, I must ask
again, where's the point in providing multiple mmap buffers--except when
using multiple CPUs to process multiple buffers at once.
>To do something simliar with just one buffer the application would
>need one extra memcpy:
>
>MCAPTURE(0)
>while (true) {
> SYNC(0)
> memcpy frame
> MCAPTURE(0)
> // process frame while hardware/driver refills frame
>}
No, it doesn't:
while (true)
MCAPTURE(0) <- effectively null operation for driver
SYNC(0) <- driver converts internal buffer into mmap buffer
// application processes frame directly in mmap buffer, no memcpy
// * hardware will continue capturing into internal buffers! *
}
There is a kind of "memcpy" when the internal buffer is converted into the
mmap buffer, but since the conversion would be anyway quite difficult to do
in-place, the copying would be likely to be necessary anyway.
