Re: FPGA for PCI based servo control board

[jmkasunich-at-ra.rockwell.com]

John Sheahan wrote:

> jmkasunich-at-ra.rockwell.com wrote:

>> The solvable problem is how to connect the FPGA
>> to the ethernet cable.  What does it cost to add
>> ethernet to an embedded project?

> starts with adding a socket, a transformer and a
> cheap part like the 8019.

> Then the 64 dollar question, Are you running IP?

NO. Raw packets.  Point-to-point connection, no
switches, hubs, or collisions.  Still need protection
against noise corrupted packets (CRC errors).

> if so - you need  the micro and a protocol stack.
>
> if not, the fpga can suck fixed formatted
> packets straight out.

Can it assemble packets and stuff them into the
ethernet chip too?  Gotta handle the inputs as
well as the outputs.  Also, do we use a fixed
format packet that includes 8 axis and 128 bits
of digital I/O regardless of the actual amount
needed, or should the packet format be determined
at boot time?  I agree that during run time, the
packet format should be fixed.

We might want a micro to handle the above issues,
but definitely no protocol stack.

> This impacts on your RT-linux  concern  too,

> firing a packet into a dedicated NIC with no
> collision concerns is not hard. (and can be
> realtime) unlike IP.

The hard part here is dealing with dozens of
different NICs.  On the FPGA end, we choose
the NIC.  On the PC end, it could be anything.

John Kasunich