On Sat, 16 Apr 2022 at 00:42, Torsten Curdt via Emc-developers <emc-developers@lists.sourceforge.net> wrote:
> IIUC the GCODE interpreter runs in the non-realtime part. It sends the step > instructions to a card to execute the steps. This is obvious when using a > LPT port, but how does this work via Ethernet? There are some steps missing here that have not been explained in later posts which might explain the process. The interpreter, as you said, runs in user space, it reads G-code and converts it in to "canonical commands" which are fed to the motion queue. These commands are the basic things that a CNC machine needs to do. It is worth noting that many G and M-codes only affect the internal status of the interpreter, and that is partly why the program line counter skips non-movement commands, they simply don't exist in te queue) Also, the interpreter is a pluggable module, it doesn't have to be G-code. There are several steps from here, including converting the commands into NML messages ( https://www.nist.gov/publications/neutral-message-language-model-and-method-message-passing-heterogeneous-environments ) but eventually the commands get to the "trajectory planner" (tp) (userspace) where they are put into the motion queue, which is consumed by the (realtime) "trajectory controller" (tc). Every 1mS the tc calculates new positions for all axes, and puts those positions on to HAL pins. What happens next depends on the system. With an LPT system the HAL "stepgen" component 1mS thread reads how many steps have been made in the last period, and from that and the new position calculates the required step-rate to hit the new position at the end of the current period. Then, in the fast thread the (integer maths only) step generator makes the pulses. With a Mesa or Pico stepper system there is no fast thread, the HAL driver does the same calculations as the LPT driver, though, but passes the required step rate through PCI, EPP, SPI or ethernet to the FPGA (or processor) on the card by writing to registers on the card. So, the cards are doing very little. As far as I know an ethernet smoothstepper does not do this. I don't even think that they "buffer" as is often suggested. In fact I think that they move all of the "tc" on to the hardware. So probing and spindle-synched motion is handled inside the card, not on the host controller. -- atp "A motorcycle is a bicycle with a pandemonium attachment and is designed for the especial use of mechanical geniuses, daredevils and lunatics." — George Fitch, Atlanta Constitution Newspaper, 1912 _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
