On Sat, Sep 18, 2010 at 3:24 PM, Slavko Kocjancic <[email protected]> wrote:
> Na 17.9.2010 23:15, Kenneth Lerman je pisal:
> > On 09/17/2010 04:26 AM, Slavko Kocjancic wrote:
> >> Peter thanks.
> >>
> >> I didn't realy calculate the worst case scenario. Just observed that
> >> acceleration is calculated on servo thread. And finding reliable PC to
> >> got 5kHz servo isn't so hard as finding good one with 15us base jitter.
> >>
> >> For 1kHz servo thread the some other interface should be investigated.
> >> I find my eeepc has 26us jitter so can be perfect for servo. But has
> >> only USB and ethernet interface.
> >>
> > That's not exactly right. It also has an SD card interface. I'll bet
> > that could be made into a useful way to get data in and out.
> >
> > Ken
> >> I think now is time to investigate that interfaces. Year's ago I make
> >> some experiment with fpga receiving ethernet traffic and sending it. It'
> >> works well. But in PC side I use regular protocol's. With low level
> >> programming PC hardvare and leave all TCP/IP stuff out might bu just
> >> right thing.
> >>
> > Stuff deleted.
>
> Ah yeah realy that port is there too. But I think it is unusable. In
> most cases it's connected to USB bus internaly. So the direct USB can be
> used instead.
> I didn't realy dig onto USB driver's and hardware. But I know that USB
> transfer at 12MHz rate (Not hi speed) and 10BaseT ethernet at 10MHz.
> That's rates can be software managed these day's in cheap micros. So the
> problem lies on PC side. I know that some overhead must be send just
> need to decide where and how. For ethernet the 6 byte MAC address and 2
> byte CRC is the minimum overhead.
> So to use Ethernet and wish to complete transfer in 200microsec then
> 1000 bits (125 bytes) can be send (and received). The problem possible
> lies just on hardware side of PC how to override buffering and similar
> RT killers. Maybe USB is easyer but I don't know as I didn't make
> anything on USB. But few years ago I send packet to ethernet with AVR
> mcu. Today that's are a lot faster.
>
I was also thinking of building a Ethernet control interface for EMC2.
The controller could be OpenRISC. It's open-source and with Ethernet IP
integrated. Please check the following links:
http://opencores.net/openrisc,or1200
http://opencores.net/openrisc,orpsocv2
-Yishin
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