Olin Lathrop wrote:
>> <checksum>: the 8 bit polynomial checksum
>
> 8 bits is very small for the size packets you are talking about.  It may 
> be
> good enough for your purposes if you don't really expect errors, which 
> might
> be applicable in your case.

I disagree. An 8-bit CRC is used in automotive protocols (including CAN), 
which were specifically designed for noisy environments.


> You also need to think about timeouts when a ACK is not received.  Think
> carefully about what happens when the ACK itself is lost.  The receiving
> node got the command, executed it, and sent the ACK.  The transmitting 
> node
> has to assume the receiver never got the command.  Most likely it will
> resend after a timeout, but you have to think carefully about what the
> receiving node might do if it receives two separate valid commands.  A
> sequence number is the usual way around this, but there are other
> strategies.

- Avoid "vague" commands ("toggle") in favor of more specific ones ("turn 
off")
- Have the transmitter request the status before issuing the command again


>> If I have other things to do, how do I create "tasks" so that
>> the real tasks such as getting data from sensors, turning off the
>> lights, and so on is done on a high priority basis?
>
> You don't need priorities, since you've got plenty of CPU time to go 
> around.
> A simple round robin task manager should be just fine for this.  Each task
> does whatever it can do immediately, then calls TASK_YIELD to let all 
> other
> tasks run once.  When a task is waiting on a external event, it sits in a
> loop checking the event and calling TASK_YIELD until the event condition
> occurs.

I'm curious, why do you think a task manager would be useful in this case?

Vitaliy 

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