comedi_mark_buffer_read — streaming buffer control
#include <comedilib.h>
int comedi_mark_buffer_read( | comedi_t * device, |
unsigned int subdevice, | |
unsigned int num_bytes) ; |
The function comedi_mark_buffer_read
is used on a subdevice
that has a Comedi input command in progress. It should only be used
if you are using a mmap
mapping to read data from Comedi's buffer
(as opposed to calling read
on the device file),
since Comedi will automatically keep track of how many bytes have been
transferred via read
calls. This function is
used to indicate that the next num_bytes
bytes in the buffer
are no longer needed and may be discarded.
The function comedi_mark_buffer_read
returns the
number of bytes successfully marked as read,
or -1
on error. The return value may be less than
num_bytes
if you attempt to mark more
bytes read than are currently available for reading, or
if num_bytes
must be rounded down
to be an exact multiple of the subdevice's
sample size (either sizeof(sampl_t)
or
sizeof(lsampl_t)
).