In article , Deloptes   wrote:
>Jan Panteltje wrote:
>
>> Linux, RT or not, is not a real time system.
>> It is a multi-tasker.
>> I usually design some extra hardware if things need to run fast and
>> continuously. hardware that includes buffers.
>> example:
>> http://panteltje.com/panteltje/raspberry_pi_dvb-s_transmitter/
>>
>> Much these days can perhaps be done with an FPGA hat (have not tried
>> that). Else you will need to do some electronic design, soldering, etc.
>> In any case you also need to write the software to interface to that,
>> You need to specify your requirements.
>>
>> Sometimes a simple PIC micro-controller is all you need to add to get past
>> the task switch interrupt.. But it will need to be programmed too.
>
>I know a guy from the mailing lists (Gene Hasket) that is operating some CNC
>and was complaining about lack of RT in linux. He is using some patched
>kernel from somewhere - I do not recall the details, but it is really a
>problem that Linux is not applicable to time sensitive applications.

3D printers pretty much always have some sort of microcontroller running
them directly...anything from an 8-bit AVR on up to ARM-compatible devices
like the LPC176x or STM32Fx families.  Any of these are sufficient for
accurately firing stepper motors, monitoring endstops and thermistors, etc.
in a Cartesian or CoreXY printer configuration; more advanced kinematics
(such as Delta or SCARA) sees more benefits from a 32-bit controller.

To the extent that a Raspberry Pi is involved in 3D printing, it's usually
just streaming gcode to the printer's microcontroller.  Even if you're
running something like Klipper (which shifts more of the motion-control work
to the Raspberry Pi), you're still streaming some sort of simplified command
sequence to a microcontroller that provides the necessary realtime control.

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