Hi, I read through the help file for pd~ and most of it makes sense, but the -fifo flag has me scratching my head. The documentation says "number of blocks for round-trip (default 5)."

I feel like the combination of external block size, internal block size, and whatever limitations are baked into the code should dictate this...
What are the ramifications for overriding the default? how do I choose a value?

thanks

Realized I might be unclear- by pd~ I mean the vanilla object called [pd~] that allows running another instance of pure data to process audio on multiple cores.

@mbbaker This is just my educated guess as someone who has written interrupt driven multitasking stuff in assembler during the Pleistocene era .

Anytime you have independent processes that have to communicate, they have to do it through some kind of buffer because the time slices that each process will receive are not under the programmer's control. Compare with cooperative multitasking using co-routines. So if 2 or more Pd processes have to stream audio between them and not miss a real-time deadline, there has to be a fifo buffer between them.

How big a buffer is required? That depends on each OS and differs from moment to moment depending on what other processes are competing for CPU time. Some processes may lurch forward in execution while others wait to be scheduled. So it can't be predetermined, and therefore it's a configurable option.

In my one project that used [Pd~}, -fifo 1 worked without issue. The lower the number, the lower the roundtrip latency between processes, so I guess that means the fifo size is a tradeoff between latency and reliability.