On Thu, 3 Oct 2019, Gene Heskett wrote:
Date: Thu, 3 Oct 2019 10:08:00 -0400
From: Gene Heskett <[email protected]>
Reply-To: "Enhanced Machine Controller (EMC)"
<[email protected]>
To: [email protected]
Subject: Re: [Emc-users] Real-Time Linux on the Raspberry Pi
On Thursday 03 October 2019 08:25:10 Thomas J Powderly wrote:
Hi Gene, PCW,
I just hooked up a second ethernet port to an rpi3b.
I ssh'd into eth1 and ran a sim axis.
pi@raspberrypi:~/linuxcnc-dev $ uname -a
Linux raspberrypi 4.14.59-rt37-v7+ #1 SMP PREEMPT RT Sun Aug 26
15:11:25 +07 2018 armv7l GNU/Linux
What tests can be run to see if this can use 'normal' mesa ethernet
cards? without actually having them ?
tomp
The 'trick' to extra ethernet port without using the usb bridge
is to use an ENC28J60 module connected to gpio pins ( no usb involved
) the ethernet is bitbanged spi
here's a link to what i did ( altho i have different pins used and a
slightly different module than he used )
https://www.instructables.com/id/Super-Cheap-Ethernet-for-the-Raspberr
y-Pi
Thats cute. But I see 2 potential problems.
1. Its half duplex, is this compatible with mesa ethernet driven cards?
2. its using the same signal lines the first spi port (hm2_rpspi.ko)
uses.
It can likely be moved of course but will need bootup options to do it I
expect. Theres a discussion about spi on the pi3, and on the pi4, but I
don't have the links handy. I think the pi3 has 2 independent spi's with
two slaves on each, AIUI, the pi4 has more cs lines allowing more
hardware to be addressed on a shared circuit basis.
3. And two last questions, how fast is it? (Went back to link, 10
megabit, not really fast enough for a mesa card) and is it reverseable?
Eg, can it be used as a pair, driving the older 7i90 card over a longer
cat5 link cable? An spi to spi link IOW? No. Not fast enough. My
currently working spi is running 4.2x faster than that.
Now if a 100 meg or even a gigabit version could be had... Interesting
idea.
Cheers, Gene Heskett
--
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-Ed Howdershelt (Author)
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- Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/gene>
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A quick test would be to ping a fast host (with say a 200 byte packet) and look
at the ping times.
Note that there is at least one person using a RPI3 connected to a Mesa
Ethernet card using the RPIs built in Ethernet with success even with
the USB bridge. They did have to lower the servo thread rate to 500 Hz...
Peter Wallace
Mesa Electronics
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