Jon Elson wrote: > John Kasunich wrote: >> What makes this situation subtly worse is that the user will have no >> clue about this latency. When he runs the RTAI latency test, the driver >> won't be loaded, so the latency that it causes won't be detected. The >> user might run the latency test, get a 15uS for a result, determine his >> max speeds accordingly, then start EMC. But every once in a while he >> will get latencies twice as large as he did in the test. If he is doing >> software stepping or software encoder counting, he'll either be losing >> steps or skipping counts, and have no idea why. >> > Btm this is for a 7i43 system (I think) and so you would > normally use the Mesa card's facilities to do this, and not have > software step generation on the same system.
Agreed, that's very much the nominal case. The use-case we're discussing here is for that freak situation where you need just *one* more encoder (say) than the available firmwares provide, and you don't have email so you can't ask Mesa for a new firmware image, and you don't have the tools/skills to recompile the firmware yourself. And sampling the GPIOs at 15 KHz would be fast enough to make the encoder work, but 5 KHz would not. In *that* situation, you might want to use this thing we're discussing, which needs to disable interrupts. Hm, when I say it that way, it makes this discussion sound sort of silly. ;-) > One possible thought is to break up these big bursts of EPP > traffic into smaller blocks, and enable the interrupts between > them. So, instead of doing 16 data cycles in one block, do 4 at > a time. This increases total traffic, of course, but allows > higher priority threads to run with lower jitter. The problem with that is that HostMot2 uses 16-bit addresses, so each EPP "burst" would need to be preceeded by two address cycles. Splitting 16 data cycles into four groups of 4 increases the total EPP cycle count from 18 to 24, a 33% increase. In addition to the address cycle overhead, it takes about 1 us to check for EPP timeout after each burst, which also adds up as you decrease burst size and increase burst count. -- Sebastian Kuzminsky Cryogenic travel has improved since then... I woke screaming in a translucent box. “There, there,” said the box. “Everything will be all right. Have some coffee.” -- Ken Macleod, "Who's afraid of Wolf 359" <http://outofthiseos.typepad.com/blog/files/KenMacleodWhosAfraidofWolf359.htm> ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
