On 1/11/2014 6:49 PM, andy pugh wrote: >> As an admitted neophyte to this space, you can tell me to go to my >> corner and be quiet, but I can't help asking why configuration data, >> which is what the pin info is all about - startup setup information that >> can get stored locally in the driver once received - why this needs to >> be atomic. > > I think you might have a point there. Perhaps not the point you think > you have, but still a point. > > HAL makes a distinction between "pins" that are links between modules > and "parameters" which are one-eay data into a module (or, in some > cases, out to Userspace) > HAL string _pins_ are likely to cause problems, but hal string > _parameters_ could be a real boon for config (and re-config) work. > > In practice I am not sure how important atomicity is anyway. The > problems only arise when a base-thread function tries to read a HAL > pin while a servo-thread function is writing to it. I can't think of > many examples of a servo-thread pin that might be linked to a > base-thread pin, except perhaps for some parallel-port IO and it is > hard to see how bit-type values can have an atomicity problem.
Well, from what I know about HAL, the primary difference between a pin and a parameter is how the memory address pointer is passed. All the atomic restrictions apply equally to both pins and parameters, and there is no mechanism for "configured once prior to startup and not changed at runtime", which is what you'd need to implement a string longer than 8 bytes. And using a double type as an 8-byte string is just all kinds of wrong, IMHO. I'll stick with an integer numbering scheme for now, thanks! :) -- Charles Steinkuehler char...@steinkuehler.net
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