linuxcnc-2.8.0-pi4.img - no USB on raspberry pi 4 - 8GB & 2GB

It early used total_mem hack to limit DMA address zone (DMA safe zone must be <3GB address). But 4.19 has all fixes for these issues for 32-bit and 64-bit kernel. It may be another issue with >3GB but I can't find it in raspberrypi/linux github issues.

andypugh wrote:

Is there _actually_ a problem?

On my 8GB Pi4, after following the instructions here
linuxcnc.org/docs/2.8/html/getting-start...lling_on_raspbian_10

I can only get USB working by setting total_mem to a maximum of 3072.
I can do this before or after installing the realtime kernel and back an forth. Anytime total_mem is greater than 3072 my USB stops working.

andypugh wrote:

Also, can we move this discussion to one thread, ie this one:
forum.linuxcnc.org/9-installing-linuxcnc...-work?start=0#194602

Sounds reasonable as the 2GB bit in this thread title is misleading.

I'd just like to say I've just experienced the No USB with a 2GB pi 4

This is my second pi 4, the first just worked. However this second pi, I took it straight out of the box and put a linuxcnc image in it straight away, the first one I had used for other things first. Thinking that this was the issue I booted a standard raspbian image which worked as expected. Rebooted with LinuxCNC image, still no USB. So can confirm that 2GB is affected.

I will troubleshoot and see if I can work out what's going on.

Dear andypugh,

I have experienced the same issue with no USB oder Wifi with a 4G raspi 4. I have used the 2.8.0 img that was linked directly on the entry page (sorry, didn't even get as far as your getting started page). Here I had to add the 3GByte limit and it worked just fine.

Is there any advantage of now using the new 2.8.1 img? I'd rather not setup everything again, if there is not a major advantage. I am up and running with 2.8.0 and all online updates (with 3G limit of course).

Thanks for the linuxcnc image!

PS: I am all new to CNC and will build my CNC-Dötzchen in May 2021 - until then I am practicing CAD - so no experience and CNC setup yet, just prep work.

I hadn't seen that, I was still using 2.8.0, it worked fine with my earlier pi4...

Just found linuxcnc-2.8.1-pi4.img and it seems to work perfectly, thank you

I have just tested the SD image on my new RPi400. Lateny (Servo+base) is ~ 75000 as it comes out of the box.

Now I moved it from SD to a 8GB Kingston USB3 thumbdrive - write access is a bit on the slow side. I moved /var/tmp /tmp and /var/log to tmpfs, swapped from Debian to Devuan, killed anything GNOME and installed TDE. This brought latency down to 65000.

Now I disabled BT + WIFI + audio. Latency is <50000 after an hour testing.