Hi Wouter, On Tue, Jan 4, 2011 at 2:48 AM, Wouter Simons <lkml@woutersimons.org> wrote:
Hi all,
This might be a silly question, but I want to make sure I understand things correctly.
I have a driver with a sysfs entry to get the next data sample every time I read the file. Used like below it works wonderful:
# cat next 0x15814 # cat next 0x1682B
The last 12 bits are the sample and the first (20) bits are the channel the sample is from (some ADC hardware board with 24 inputs).
Now I have some C code that will loop periodically to collect the samples and do some magic with them and I was hoping I could simply keep a FILE * open with a loop like this:
for (i = 0; i < count; i++) { if (fscanf(fd_next, "0x%X", &sample) != 1) { /* No data */ continue; }
I would change this to use unbuffered I/O routines (i.e. open/read/lseek/close) and use sscanf rather than fscanf. fopen/fread/fseek/fclose use buffering by default. That would eliminate any buffering that the user side runtime library is doing. I suspect that because the data is buffered by the FILE * routines, even doing the seek is just re-returning the data that was read the first time around. Dave Hylands