Am 11.01.2014 um 05:19 schrieb andy pugh <bodge...@gmail.com>: > On 11 January 2014 02:59, Charles Steinkuehler <char...@steinkuehler.net> > wrote: >> I think I've come up with a reasonable solution >> that will still work with HAL's limitations (only bit, integer, and >> float data types, so no strings). > > Wacky idea, why not add strings to HAL? (if you do, then I suggest > _not_ zero-terminated) > > it could be useful for all sorts of config type stuffs
yes it would, but as Charles says: it would break the atomic update requirement assumed by HAL data types. You cant guarantee a string copy will not be interrupted; for the basic types you can. This guarantee maxes out at 8 or 16 byte sized values, depending on architecture, so it's unsafe territory beyond 8 and architecture dependent. HAL assumes sizeof(double) can be updated atomically as largest object (8). This means strings may travel to/from RT components on a message queue, but not as pins the difference between sending/receiving a message and updating a HAL pin is that the message creation/interpretation code may be interrupted as long as the enqueue/dequeue operations are atomic, which they are in Pavel's ringbuffer code; interruption may not happen for pin updates in the ringbuffer variant this is the sequence 'reserve space in queue', and 'enqueue'; both are atomic - any interruption between the two permitted the legacy code does not have an atomic enqueue operation but checks on the receiving side that enqueue operation is complete (in case you've ever wondered what the SPLIT_READ stuff is - that is detecting 'enqueue commit' on a queue which must be size one, so it's really just a shared buffer) -- if you are just dying to transport a short string of max size 8, you can recycle a HAL_FLOAT, interpret as char[8] and it would be atomically updateable _by storing/reading a double (not using memcpy() etc!), but it's royal wart and it stinks. The solution to this will be making messaging interactions between components trivial, then the issue goes away. Right now it's jumping the hoops. - Michael ------------------------------------------------------------------------------ CenturyLink Cloud: The Leader in Enterprise Cloud Services. Learn Why More Businesses Are Choosing CenturyLink Cloud For Critical Workloads, Development Environments & Everything In Between. Get a Quote or Start a Free Trial Today. http://pubads.g.doubleclick.net/gampad/clk?id=119420431&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
