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Old 07-08-2008, 10:43 AM   #1
mmcshmi11
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Query buffer with serial port /dev/ttyS0


Hi all, I'm now trying to query what the size of the buffer is without actually reading it. I currently write to /dev/ttyS0 then query and then read the data. I'm just writing ABC and then receiving the same thing when I read, but the value I get when I query is something like 766 bytes (or something weird like that).

This is my call:

int bytes_avaiable;
ioctl(num, FIONREAD, &bytes_available);

I've also tried I_NREAD instead of FIONREAD, but I'm not sure what is going on. Is the value of 766 what I should be getting for the number of bytes??
 
Old 07-08-2008, 11:31 AM   #2
mmcshmi11
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I'm been messing around with this and now think it's some kind of timing issue. As I changed the value of usleep() after my write but before my query_buffer, the value query_buffer returned changed. If I increase the amount of data sent to the serial port, it requires a longer sleep or it can't read anything.

However, the value query buffer returns just continues to rise as I increase the time sleeping. Does this mean that it's constantly sending info to the port even while it's sleeping? and even when I say to only send 10 bytes?
 
Old 07-08-2008, 04:24 PM   #3
mmcshmi11
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FINALLY

Ok, I figured it out, all the echo had to be turned off:

stty -F /dev/ttyS0 -echo -echoe -echoke .....

Echo isn't so nice for a loopback test
 
  


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