> Is the real time component of Linux CNC running all the tasks that are > > started with the loadrt with a 24uS period? In other words all loaded > > "loadrt tasks" have to finish within 24uS or the system will start to have > > jitter or miss events. > > > > No, only the functions that are addf-ed to the base-thread run at that > rate. Everything else (addf-ed to the servo-thread) runs at the > servo-thread rate. > This typically includes motion and the management section of many > components. So, for example, the stepgen has a servo-thread part that > calculates the step rate, and a base-thread portion that _only_ makes > steps. > Generally nothing in the base-thread does any floating-point calculations. > (base-thread FP used to be disallowed, in fact, but can now be turned on > via a switch) > > > In general yes, but the parallel port is a special case. It has a "reset" > function that can be configured to switch pins back to their default state > in the same thread cycle as the parport-write. > (The parport reset will actually busy-wait if the time has not yet elapsed, > so it is more efficient to put some other base-thread tasks between > parport-write and parport-reset in the base thread to avoid waiting, except > in cases where you need the parport pulses to be as short as possible > (which I can't think of a use-case for)
Thanks Andy, A small lightbulb just went on. The loadrt loadrt hal_parport cfg="0 out" just tells the OS that there is a function rtapi_app_main() that must be called to setup the list of functions that can be addf'd. It's then the addf function names that must be exported in the rtapi_app_main() function. The "addf functions _time_-thread" then add the functions to the real time OS task list running at BASE_PERIOD and they are added in the order they are in the HAL file. So below here: ====================== # ESTOP and Charge Pump Support for safety loadrt estop_latch loadrt charge_pump # Control of PWM for Spindle addf pwmgen.make-pulses base-thread # Monitor Parallel port inputs addf parport.0.read base-thread #Control of Parallel port step/dir/output signals addf stepgen.make-pulses base-thread addf parport.0.write base-thread # make parallel port step pulses shorter than one base period addf parport.0.reset base-thread ======================= Having the parport-reset right after the parport-write means it sits in that while loop wasting time until the system clock in nano-seconds passes the set point of system clock + 5000 nanoseconds. But if I move things around so there are more addf functions before the addf parport-reset I may find it doesn't spend any time in that do wait for timeout loop. ====================== # Monitor Parallel port inputs addf parport.0.read base-thread #Control of Parallel port step/dir signals addf stepgen.make-pulses base-thread addf parport.0.write base-thread # ESTOP and Charge Pump Support for safety loadrt estop_latch loadrt charge_pump # Control of PWM for Spindle addf pwmgen.make-pulses base-thread # make parallel port step pulses shorter than one base period addf parport.0.reset base-thread ======================= John Dammeyer _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
