[Discuss-gnuradio] Regarding 371 samples/frame in usrp2

[Mattias Kjellsson]

I have been playing with ioctl's today and while browsing the USRP2- 
code i found that max length of a packet is defined to 371 which results 
in 1484 bytes of "data", and 16 bytes left, leaving room for the 14 byte 
ethernet header, but not a 372:nd sample, since each sample is 4 bytes.

But when I look at the output of ifconfig my MTU is set to 1500, but 
when I print out how much data is received from a raw socket (listening 
to some random network traffic), it tells me it reads max 1514 bytes, 
which I figured is 1500 bytes of data, and 2*6 bytes mac- addresses + 2 
bytes of protocol. This gives me two questions. Is there (probably) 
something I missed here, or should we be able to increase U2_MAX_SAMPLES 
to 375 (1500/4 = 375), not that four samples might make a huge 
difference in the end, but still... And the other question, shouldn't 
one check for the MTU set by the nic and calculate this number, instead 
of having it #defined? But then again, it would be a whole lot of re- 
writing, since U2_MAX_SAMPLES is #defined... Or have I missed some 
fundamental here?

BR
Mattias Kjellsson