Raspberry Pi 4

Hello

OK Cheers. Will do the lcnc install soon. and report back

rt-tests are part of Debian

So
apt install rt-tests
The stanza I used is kinda std. Gives min, avg, max...
Broad cli window to see all detail
More intimate detail in man pages & www

Seems that with every linux kernel iteration the realtime thing gets worse...
Having said that I found Stretch was circa 580uS So????
Good times are just around the corner....

Cheers
MrGreg

Hello

OK Lcnc latency-test: 1ms servo

As per previous with rt-tests cyclic:
Hard labour- glxgears @ 1080p, web browser (Firefox) 4 tabs, javascript & stuff etc IE same as before.

Hmmmm

840uS

Bit of extra info, again same conditions as before.
CPU from panel monitor 72% steady +- 2
ditto temp 52deg steady +- 2 ( I have massive passive heatsink )

No activity on core4 ( you knew that ) circa 95% other 3
Similar jumps in latency as previous test
10~20mins 320uS
~ 40 mins 370uS
~ 70 mins 470uS
~90 mins 840uS

I wasn't actively doing anything when the last two jumps took place. Guess this is background tasks/H-keeping stuff?
Overall a slightly longer duration ~ 100mins
I couldn't say for sure whether the last large jump was captured before when doing cyclic test as the duration was slightly longer this time. The pattern and figures look quite similar, apart from the last.

More alchemy and magic needed. Not to mention time ...
What next?

Cheers
MrGreg

@MrGreg
Have you run this via ssd
Mike

@ Mike
Err No
SD
Samsung Evo

Cheers
MrGreg

Sorry, c'ant decrypt
Err No ??
The rest i interpret as you use SSD Samsung Evo
I was wondering if sometimes writing to the shdc card give those spikes. I decided not to use my pi4 as long as they have not yet realized the usb boot.
Thx Mike

@ Mike

No, not an ssd

I am using a 32GB Samung Evo+ SDHC

Could be SD writes? I have the 4GB version, so no need to access swap.
Prob could throw some read/writes into the mix to emulate next time.
I'm looking at using rt-tests to do a latency trace. I'll post that up shortly.

Cheers
MrGreg

Hello

Following on from previous

rt-tests can apparently do a latency trace.
See here foe info/example:
taste.tuxfamily.org/wiki/index.php?title..._source_of_latencies
And man page
manpages.debian.org/stretch/rt-tests/cyclictest.8.en.html

Just tried it
It works on Gene's RT kernel

Just a "simple" matter of finding and eliminating them.....
Well....Might be helpful? TBD

Cheers
MrGreg

Thx Andy,
I will read up on mmap and the way hostmot... handles gpio pins
I had thought of using an array og bytes, one byte per pin, with bits for each 'feature'
But i hant though of how users enter the information.
There a re a LOT of pins to describe on these various devices.
thx
tomp

MrGreg
I tested Genes and my own kernel a lot over the last 2 days
There's not a lot of difference between them
I built mine from JT's instruction on Feb9 ( so had some newer pkgs than JT had )
I have different monitor than Gene
I have the npt fix from samco
see
and i force 600mhz AFTER booting ( not automated yet)
sudo sh -c "echo -n 600000 > /sys/devices/system/cpu/cpufreq/policy0/scaling_min_freq"
sudo sh -c "echo -n 600000 > /sys/devices/system/cpu/cpufreq/policy0/scaling_max_freq"
sudo sh -c "echo -n performance > /sys/devices/system/cpu/cpufreq/policy0/scaling_governor"

My system is responsive and videos smooth enough for me (infrequent blips i cant blame on anyone in particular)

here what you can expect:
run
latency-test period
then
IF you really beat on the system
like 4glxgears, 2 resized to larger
and chromium browser showing youtube video full screen, then back to default size so you can see the katency dialog
>I< get 106 usecs ( very long test )
IF you are nice to it ))
like 4 glxgears, no resizing, hands in pocketses
>I< get 50uS ( 13 hrs )

and here's some pix...

conclusion: MY OWN
iF you use it like a 1 bladed swiss army knif, you wont be developing and surfing and gaming
and you rely on the DRO ( not gui ) during cutting
THEN you can use a rpi3 or 4 to controll a slower stepp using gpio
a medium speed stepper using PiCNC
a high speed stepper using SPI with Mesa cards

YMMV but not a lot
HTH

tomp