But....with a scheduler wouldnt you normally have to restore a whole stack context for the task you are trying to let resume? That could not be done by setting the SP to point to various places within the higher interal RAM space, or by block copying context data into the stack area from XDATA (the VERY inefficient method).

Whatever......schedulers on an 8051 are unnecessary as it is possible to write simple state machines and round robin task subroutines that are called from a main executive loop --- All on a single stack context.

I have done some pretty complex things with many activities going on at one time in a microcontroller and never had to use a scheduler or RTOS. And I can relate that a couple of companies I am familar with thought that they needed an RTOS on a small microcontroller and afterwards wished that they had not tried to implement it.

Michael Karas