Thanks guys, you've given me some things to chew on.
On 1/4/2024 10:05 AM, gene heskett wrote:
On 1/4/24 05:33, Rod Webster wrote:
just á hunch - Rod knows more than I do.
I know nothing!
Methinks the lady protesteth too much. ;o)
My gut feel it is a linuxcnc or Mesa issue. Isn't there a driver
involved
on our side? I just don't know anything abou the hardware interfacing
side
on the pi
The foundation doesn't share that info willingly.
spi is a different critter, and hardware wise can be very ticklish to
setup correctly. For instance, its almost the only interface that uses
"source termination", some of the ohmage used does not sound right
until the resistance of the transistor driving it is included but that
is more often that not just a SWAG. My cable from the pi to the mesa
card is only about 1.125" long, accomplished by turning the pi upside
down which probably helps. I also used an interfacing board Jon E.
made that carry's the terminating grain of sand 120 ohm resistors,
which approximates the characteristic impedance of the common ribbon
cable, assumed in most texts to be around 122 ohms. This absorbs the
echos bouncing back and forth on this cable and w/o those the signals
will bounce from end to end a lot worse leading to data errors. To
understand better what is going on, read up on VSWR. I am a retired
broadcast engineer and a CET, am astounded that the number of EE's out
there never had a prof that understood the subject, but IMO were
cheated by not spending a semester or 3 to get a good, working
understanding of the subject. Their professors are IMO cheating them
by not covering the subject.
If you look at a digital signal with an o-scope fast enough, the
spikes you see on the edges where the signal changes, are caused by
VSWR and poorly terminated lines. The ideal situation is a wire whose
impedance is known, driven by a signal source of infinitely low
impedance, with a resistor in series that matches the cable in value,
driving any length of that cable, with the far end of that cable
loaded with that same matching resistor. Send a 2 volt signal at the
source, you get a 1 volt signal any place on the cable, subject to the
time delay as it travels thru the cable at a large percentage of C
speed. There is little or no echo, half the power is in the two
resistors. if the resistors are miss-matched and don't match the
cable, some of that signal will be reflected as if it was a mirror by
the load end and sent back thru the cable to the source, bouncing back
and forth until the resistors have finally absorbed enough that the
receiver sees the valid data represented by the instant voltage at
that time.
That's about as simple as I can make it. CET's are the cream of the
crop on this, most EE's cannot pass the CET test. The converse is also
true.
But there's one of me for every 100+ EE's. I'm NB-116, dated in 1972.
18 years later they had issued NB-122.
As a machinist I probably suck, at 89 yo I'm still learning,
electronics I'm pretty good at.
Take care, stay warm and well everybody.
Rod Webster
*1300 896 832*
+61 435 765 611
Vehicle Modifications Network
www.vehiclemods.net.au
On Thu, 4 Jan 2024 at 18:55, Steffen Möller via Emc-developers <
emc-developers@lists.sourceforge.net> wrote:
@Chuck,
Not for controlling anything because of truly evil latencies, but
without
any motors attached you may want to check if the SPI errors also
show when
running the official Raspbian OS. This could be an indication of some
firmware issue - or some timing parameters - or ... just á hunch - Rod
knows more than I do.
Best,
Steffen
Gesendet: Donnerstag, 04. Januar 2024 um 08:46 Uhr
Von: "Rod Webster" <r...@vehiclemods.net.au>
An: "EMC developers" <emc-developers@lists.sourceforge.net>
Betreff: Re: [Emc-developers] RPImager problem Re: RPi5 + Raspbian +
LinuxCNC latency tests - first impressions
If the R-Pi guys are being responsive, I wonder if you find any
answer
about the SPI interface for the Mesa boards? I found that linux-cnc
reported SPI errors when trying to talk to the 7C81.
Chuck, I'm sorry but I don't know enough about the topic to frame the
question. Lets see if they can sort out the sound first.
you can find them on Discord #arm-img-builder which is linked to from
their
repo I forked https://github.com/pyavitz/rpi-img-builder
Rod Webster
*1300 896 832*
+61 435 765 611
Vehicle Modifications Network
www.vehiclemods.net.au
On Thu, 4 Jan 2024 at 07:09, Chuck Peplinski
<chuck.peplin...@gmail.com>
wrote:
If the R-Pi guys are being responsive, I wonder if you find any
answer
about the SPI interface for the Mesa boards? I found that linux-cnc
reported SPI errors when trying to talk to the 7C81. I'm new to the
Linux-CNC community, so maybe I'm doing something else wrong. But I
got
the idea on the forums that there was some known issues with SPI
on the
R-Pi5.
It's been on my list to follow the build instructions and see if I
could
find out more, but that hasn't happened yet.
Thanks,
Chuck
On 1/3/2024 1:39 PM, Rod Webster wrote:
Thank you for that pointer, I checked and found it installed but it
does not find any input or output devices.
Upstream have resolved the rpi-imager compatibility issue.
Their sound guy is away for a few days but has it on his to do
list.
The willingness to sort this out has been amazing
I have to find time to merge the changes and rebuild it. I Am flat
out
for
a while.
Rod Webster
*1300 896 832*
+61 435 765 611
Vehicle Modifications Network
www.vehiclemods.net.au
On Wed, 3 Jan 2024 at 22:27, Steffen Möller via Emc-developers <
emc-developers@lists.sourceforge.net> wrote:
On Tue, 2 Jan 2024 01:49:34 +0100
Steffen Möller via Emc-developers
<emc-developers@lists.sourceforge.net> wrote:
The regular raspbian OS comes with sound via HDMI. I am toying
around
with packages to install to see if I am getting anywhere without
much
configuration. KDE works after installing task-kde-desktop - no
sound, though.
Install the pavucontrol package. That hass the controls you need
to
move the sound between ports.
Thank you for that pointer, I checked and found it installed but it
does not find any input or output devices.
Best,
Steffen
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Cheers, Gene Heskett.
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