On Wednesday 25 May 2005 03:09 pm, Byron A Jeff scribbled:
> There's no real point in have double transmissions if nodes need to talk
> directly to one another. Primary/secondary based systems work best when all
> of the secondaries need to interact with the primary.

I came up with this since in a significant majority of cases, the master will 
need to be informed of the event, and the slave will want to communicate the 
message to more than one other slave.  Having each slave send out a message 
to more than one other slave seems like a mess as they would be communicating 
without the master letting them do so.

I also thought of a scheme where each bit on a couple bytes would represent a 
unique node.  In one message, multiple specific nodes could be addressed.  
But this turn out to be another can of worms for the acknowledgements.  All 
sorts of odd thoughts of having each station acknowledge after waiting a 
specific differing time followed, which resulted in my head spontaneous 
combusting. :-)


> > - I'm planning to implement an acknowledgement to the slave that message
> > was received.
>
> That will facilitate flow control. But how will you know when the addressed
> node is finished sending?

FIxed length messages.  So far 3 bytes per message, which includes the 
address.


> But that doesn't jibe with "about 10 ... planning to allow for 16". Either
> it's fixed and you hardcode it, or it's not and you allow new stations to
> join.

Allowing for 16 in case needed in the future, and with this scheme, I'll have 
some simple flags in the code to indicate which types of messages need to be 
send to which stations (depending on the type of station).  I'd need to set 
these flags in the code for the new station ID and re-compile.  By planning, 
I mean that I will not need to re-write the code using a different message 
length, etc -- just set flags and re-compile the firmware.


> It feels like you picked the primary/secondary model out of thin air. Token
> passing is more flexible and also eliminates contention.

There is another term to descibe where it came from, but I'll refrain from 
stating it here :-)  Okay, not really -- the need to have a message mostly go 
to multiple stations made this scheme somewhat "natural" (at least for me).  
I'll do some thinking about the token method.


Thanks,
-Neil.

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