Re: general control thoughts

>I think the easiest way to do this is for a point to point network or
>even a network with a hub is to use raw ethernet packets.  An ethernet
>packet has a payload of up to 1500 bytes. That should be large enough
>for most things we would want.

>On top of the payload we have around 20 bytes of overhead, including a
>CRC. I think we could come up with a simple polling protocol. The EMC
>machine would be the master.

>To me, the thing that needs the most thought is how to build a generic
>HAL component to handle this. It is the same problem that SWP and I
>discussed at Fest regarding Modbus. Ideally, you could have a
>configuration file for the driver that specified the devices (in the
>case of ethernet if would be by MAC address) and how to map HAL pins to
>channels on the device.

Ken,

I needed to do something like this for a printer network interface a long
time ago.

By using UDP vs TCP/IP you remove all the overhead of the TCP/IP stack.  At
the HAL parallel
port interface do a Network UDP send using a very small packet with the 8
bit parallel port output
data (or maybe several sets of port data).  Always expect an immediate
response from the addressed device
with the port status.  You can tag the UDP packet with a running count to
verify the response is from
the sent packet.  It also lets you know when the network went south for