Jonatan Magnusson napsal(a):
fre 2009-03-27 klockan 13:58 +0100 skrev Ladislav Vaiz:
Hi Jonatan,
I use my own wrapper around ftdi_read_data. It returns immediately when
error occur or any amount of data is read. Timeout should be measured
with good precision.
Lada
int my_ftdi_read(struct sconn *sconn, void *data, size_t len, int
timeout_ms){
int ret;
struct timeval start, stop;
int usec, sec;
gettimeofday(&start, NULL);
while(1){
ret = ftdi_read_data(sconn->ftdi, data, len);
if (ret) break;
gettimeofday(&stop, NULL);
usec = stop.tv_usec - start.tv_usec;
sec = stop.tv_sec - start.tv_sec;
if (usec<0) usec+=1000000,sec--;
if (sec>timeout_ms/1000) break;
if (usec/1000>timeout_ms) break;
usleep(1000);
}
return ret;
}
Hi,
That consumes a little more CPU than I was hoping for, but I will do
something similar.
You can increase sleep argument but you will loose precision.
Btw, what are you doing with usec there? I don't think your code will
work with a timeout of 1200 ms for example: usec will never reach
12000000, so it will exit when sec > timeout_ms/1000, that is after 2
seconds.
You're right. I've used it only for shorter timeouts. Should be:
if (usec/1000 > timeout_ms % 1000) break;
I do it like this:
...
gettimeofday (&stop, NULL);
ms = (stop.tv_usec - start.tv_usec) / 1000;
ms += (stop.tv_sec - start.tv_sec) * 1000;
if (ms > timeout_ms)
break;
...
OK, It's possible.
Oh, I didn't know about that comma-separated list of expressions syntax
you're using (usec+=1000000,sec--), nice!
It's same as
if (usec<0) {usec+=1000000;sec--;}
http://en.wikipedia.org/wiki/Comma_operator
Lada
libftdi - see http://www.intra2net.com/en/developer/libftdi for details.
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