A recent thread on emc-users discussed the value of hal drivers having dedicated functions to read & write the gpios, without reading & writing everything else (ie: encoders, stepgens, pwmgens). The utility of this interface is clear. This interface is easy to provide for hardware where the I/O is threadsafe, such as PCI cards, but it's harder to do it on hardware where the I/O is not threadsafe, such as EPP. To ensure atomicity in RTAI of the EPP address cycles and the subsequent EPP data cycles, the driver must turn off interrupts.
I've implemented this and it works well. The code is in my experimental hostmot2 branch here: <https://code.launchpad.net/~seb-highlab/emc/hostmot2> The interesting bits are in hm2_llio_read() and hm2_llio_write(), starting on line 649 of hostmot2.c: <http://bazaar.launchpad.net/~seb-highlab/emc/hostmot2/annotate/473?file_id=hostmot2.comp-20080324150436-3zy8ulsbxdch5jua-5> The code turns off interrupts before starting an EPP transaction and re-enables interrupts when the transaction is finished. (It only does this for the EPP boards, the PCI boards dont need it.) A typical EPP transaction for this driver consists of two address cycles and 16 data cycles, for a total of about 20 or 25 microseconds of no interrupts. It occasionally (rarely) spikes as high as 75 microseconds. There's a judgement call here, and I seek your advice. Is 25 microseconds too long to run with interrupts off? -- 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
