On 03/04/2012 04:10 PM, George Nychis wrote: > > I totally like and support your idea and would love to help realizing > it. Using the timestamp logic inside UHD as a reference is a great idea > that also came to my mind a while ago. > There are a few things from the architecture point of view though that > need to be discussed. Let's take a CSMA MAC as an example, I guess that > goes into the right direction :-) Just having the "if channel free, > transmit packet"-logic inside the FPGA wouldn't make much sense in a > multi-user environment. What would happen is that if the channel is busy > and multiple nodes have packets in their tx queues, they would all end > up sending their packets more or less at the same time after the channel > gets idle again (assuming all nodes are in sensing range). In a > practical system, one would now start to move parts of the CSMA state > machine, i.e the random backoff, into the FPGA. Trying to control this > via UHD is probably a bad idea as UHD's main business is transportation. > > I do think we need something like what you have suggested but I am still > a bit puzzled about the right way of implementing it. > > > Hi Andre, > > Yeppp, the idea is to build part of the MAC in to the FPGA... the part > that requires low latency operation. So, after the simple "transmit > when idle" logic, you put some basic form of back off in to the logic > also. > > I have a paper which argues low latency MAC functionality should be > built in to the FPGA, but controlled from the host, otherwise it's as > good as worthless implementing it on the host. If you try to build this > part of the MAC at the host, the latency of receiving the channel state > (latency from FPGA -> host), making a decision and performing an action > (host -> FPGA), completely makes the information stale. You end up with > a decision that is something like 1-2ms old, which clearly the state of > the channel changes at a more finer-grain than that.
Well, I believe it's just a matter of scaling the whole system by the right factor. Information that is 1ms old can still be valuable if it still represents the truth. I just don't want to loose all the flexibility of software by moving the critical but interesting things to hardware. But of course, it all depends upon your goals. -Andre _______________________________________________ Discuss-gnuradio mailing list [email protected] https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
