[Discuss-gnuradio] OOT Blocklength

Hey all,

In synchronous OOT blocks or sinks the length is defined by the system, because I get the parameter noutput_items, but when I have a source, which block size should be used ?
And how does the system 'know' how many memory it should reserve ?
I tried sending one data value each call, but this reduced the maximum sample rate below 100ks. With 256 data words it works, but is that 'good' ?

Thanks
Franz