Raspberry Pi 4

The /boot directory generally sits on a fat partition and will automatically mount on Windows, Mac and of course Linux. Remove the S.D. card, stick it into an appropriate card reader on another system, and edit the file.

What's the whole content of cmdline.txt ?

It would appear that the kernel is looking for the root filesystem but can not find it to mount.

thadwald & BeagleBrainz...thank you!

Opening the S.D. card on my windows computer allowed me to edit the cmdline.txt file...as I thought, I left out a space when appending the line! Stupid mistake.

PCW wrote:

COlger81 wrote: Peter,
Assuming that i can get the latency issues worked out. Do you see any issues running Pi4 4gb reliably with ethernet based Mesa boards and PWM signal generation?

I have not done much work with the RPI4 over Ethernet, just SPI.
Forum member skunkworks has been running a RPI4 with a 7I92 for a few
Months now and I don't believe he has any major issues _but_
he did need to run the servo thread at 2 ms (500 Hz) rather than
the standard 1 ms (1 KHz). This may or may not be an issue depending
on the required acceleration. I have been running SPI based cards at 1 KHz
without issue, though you cannot get away with running videos at the same
time as LinuxCNC is running.

That's interesting. Is the SPI interface "generic" meaning that it's not specific to the rpi? There are plenty of more powerful SBCs than the Rpi, I'd be curious if they can work with the hm2 spi interface. Maybe not physically with the GPIO headers but if they were wired up as such would they likely work?

blazini36 wrote: That's interesting. Is the SPI interface "generic" meaning that it's not specific to the rpi?

To an extent. I think that the LinuxCNC-side SPI driver would need to have things like pin and registers changed to work with a different SBC, but the Mesa card would be entirely unaware what was on the other side of the interface.

Also the LinuxCNC Hostmot2 driver is very well abstracted to not care what interface the hardware is on. For example the identical code runs the stepgens on cards connected by SPI, Ethernet, Parallel port or PCI.

The hm2_rpspi driver is RPI specific, but the hm2_spi driver is generic
(it uses the kernel SPI driver) The issue with hm2_spi is that the kernel
driver may or may not be written with real time considerations.
For example on a RPI, the hm2_rpspi driver has considerably better
performance than the hm2_spi driver

It might be worth trying hm2_spi on some random SBCs