Re: [Discuss-gnuradio] Question about UHD driver

[Marcus Müller]

Hi Mark,

as interesting as your point is, that's not something that
can be fixed within the scope of GNU Radio or even UHD...

Anyhow, I'm not really convinced that multiple DMA transfers are always 
faster than copying data using memcpy - at least if those DMA transfers
copy only a few kilobytes, as is the case with packets from network devices.
The fact that packets are of limited size is not really a problem of 
current computing architectures - it's a consequence of having packet 
networks. Of course, it would be nice if your hardware would be able to 
actually stream data into your userland, that somehow has the (zero 
overhead) capability to tell the hardware to send the next sample - but 
in reality, hardware-to-cpu-transfers usually happen en block, and that 
is just fine for most applications, since there is little use of having 
samples one after another; therefore, some buffering is always necessary 
(and will always be).
For the sake of adaptivity, hardware supplied data most probably won't 
be written to copy device data to multiple RAM addresses, since the data 
from the device usually needs some processing (hence the driver).
So in effect, in most imaginable cases a device will do a single
DMA transfer to RAM.

Greetings,
Marcus