comedi_mark_buffer_written — streaming buffer control
#include <comedilib.h>
int comedi_mark_buffer_written( | comedi_t * device, |
unsigned int subdevice, | |
unsigned int num_bytes) ; |
The function comedi_mark_buffer_written
is used on a subdevice
that has a Comedi output command in progress. It should only be used
if you are using a mmap
mapping to write data to Comedi's buffer
(as opposed to calling write
on the device
file), since Comedi
will automatically keep track of how many bytes have been
transferred via write
calls. This function is
used to indicate that the next num_bytes
bytes in the buffer
are valid and may be sent to the device.
The function comedi_mark_buffer_written
returns
number of bytes successfully marked as written,
or -1
on error. The return value may be less than
num_bytes
if you attempt to mark more
bytes written than the amount of free space currently available
in the output buffer, 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)
).