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New To RTOS

Posted by Nobody/Anonymous on March 20, 2007
I am playing with RTOS before attempting to port it to a chip for a project. What is the minimum memory that it will run on? I'm using the Cygnal port, but with a much weaker chip than the original chip used in the demo port. My chip only has 256Bytes of ram and 8k of flash, So i want to know if it would be worth it to downsize the demo footprint to fit it on chip if it wont run anyways...

Thanks
J.T.

RE: New To RTOS

Posted by Nobody/Anonymous on March 20, 2007
Also. The demo file seems to make use of SFR Paging in context switches, which I can't do with my crappy chip. :( I feel an impending sense of doom.

J.T.

RE: New To RTOS

Posted by Nobody/Anonymous on March 20, 2007
I dont think you have enough ram to do anything nice :-(

RE: New To RTOS

Posted by Nobody/Anonymous on March 20, 2007
Anything nice, or anything at all? I just want 2 tasks, and a chance to get used to the RTOS architecture. I figured if a 32 bit arch gets it done with around 350 bytes for a couple of tasks, an 8 bit should be under 200 bytes.. Am I wrong?

I'm going to move to a different 8051 later on, so I assume it will be best to start with the small version on a similar MC. Otherwise I would just look at one of the emulation demos on the keil arm7 or PC ports.

(And is it uC or MC?) :)

J.T.

RE: New To RTOS

Posted by David Hawks on March 21, 2007
> Anything nice, or anything at all?

You probably would not be able to do anything nice. I think you could get _something_ going with two tasks and the scheduler on only 256 bytes of RAM. This would require some work, though. The Cygnal port uses the large memory model of SDCC. Since you have no XRAM, you would have to move to the small memory model. Also, the port saves each task's stack in XRAM on a context switch. You would have to modify this code to just save and restore the stack pointer instead. Your stacks would necessarily be quite small because all of the OS data structures would have to reside in the same 256 bytes.

Eliminating the SFR paging scheme of the more complex Cygnal parts is really simple. Just switch out all references of SFR pages in the code. It is much easier to get rid of SFR paging support than to add it!

Good luck and let us know if you get it to work!

P.S. According to Wikipedia, it is uC over MC. However, I think MCU is a more broadly used abbreviation.


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