Re: Which embedded system would you use?

On May 4, 10:11=A0am, 1 Lucky Texan <alcky...@swbell.net> wrote:
> On May 4, 6:36=A0am, Sink0 <sin...@gmail.com> wrote:
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> > A research,
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> > Which digital and wired communication system would you use for the
> > following robotic system.
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> > A system composed by a PC/104+ (it is just a very compact standard PC)
> > with Xenomai (or maybe RTAI), and some sensor nodes (something like
> > 12, but could vary a lot). These sensor nodes are basically composed
> > by a DSP/MCU/DSC (not the same one on every node) and some sensors and
> > actuators. The sensors can be anything so i will not give any fixed
> > description, but a good example would be a Brushless motor (with the
> > control routine inside the MCU/DSC), and 4 to 5 sensors with a max
> > sample rate of 2ksps. Basicaly the PC/104+ should get all the data
> > from sensor nodes (the MCU will handle the communication on the node
> > side) perform some processing and send back some reference to the
> > actuators control routine. The whole system should work with a 500us
> > period. The max acceptable latency between the PC/104 ask for the data
> > and the reception should be 100us, and the maximum latency for the
> > actuators command should be 70us (bewtween teh pc104 send and the node
> > receive). From all the commercial standard availables, all i could
> > find was Ethercat and Firewire, that have a chance to handle this
> > communication..Any idea? Just a final comment. The system should have
> > the minimum amount of cables possible and the max distance between the
> > PC104 and the nodes is 3m.
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> > Thanks!!
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> As for reducing cables, look into Zigbee.
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> www.winsystems.comand other makers offer boards with Zigbee.
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> Otherwise, I think ethernet might be a good choice. Or USB 3 perhaps.
> Much depends on the 'horsepower' in the node/sensor units I guess.

I need some high Reliability in this system, and wireless is not that
reliable. Anyway, i cant belive Wifi, or any other wireless interface
controlled by a RT Linix could achieve my Real Time requirements...
just to make it clear, 100us is for a round read, and not a single
node...

But thank you!

On May 5, 1:25=A0am, Sink0 <sin...@gmail.com> wrote:
> just to make it clear, 100us is for a round read, and not a single
> node...

You have not nailed down how many nodes, but KISS is always best.
If you use a Stub.Star RS232/485/422 at 1MBd, that's bog-standard
parts, and you can send 10 bytes in 100us, but the Stub.Star shifts
the bandwidth issues from the link, to the Stub.
 eg You need 16 UARTs to serve 16 star points, which should bold onto
PC/104 easily, and the higher bandwidth is on the daughter PCB, NOT
the links.
Debug/modify/Test of Stub.Star is also very easy.

 RS232/422 allows 10 bytes in both directions. inside 100us

 Choices are SPI or parallel blocks, from the usual suspects of Maxim
(I see they now have a SPI UART with Profibus speed spec & many do
Profi bus drivers)
NXP, Exar, etc

 Numbers like MAX3107, SC16IS762, XR20M1172 for SPI, or try
XR19Lxxx for a Dual Parallel model, Line Drivers included !.
 If you choose larger FIFO models with HW handshake, you can even load
all channels, and launch all syncronised with a handshake line.

-jg