On Sat, Aug 13, 2011 at 3:50 PM, Isaac Marino Bavaresco <
isaacbavaresco@yahoo.com.br> wrote:

> Hello folks,
>
>
> This week I revisited my SimpleRTOS
> (<http://www.piclist.com/techref/member/IMB-yahoo-J86/SimpleRTOS.htm>)
> and ported it to PIC24 devices.
>
> The first incarnation was just a theoretical proof-of-concept, but the
> new implementation is very practical. I'm planning to use it in some
> real-world applications. I took some ideas from FreeRTOS
> (<www.freertos.org>) but the entire code is my own work, together with
> some new ideas from myself.
>
> It uses the concept of co-routines and is co-operative, which means that
> all the tasks must call 'Yield' (or 'Delay', etc.) somewhere to allow
> the others to run.
>
> Note: 'Delay' should be 'Sleep', but there is already one macro with
> this name defined by MPLAB C30.
>
>
> I got impressed myself with its performance. Some facts:
>
> The kernel uses just 664 program words and 16 bytes of RAM. Each task
> created uses an additional 22 bytes of RAM (plus any data it needs for
> doing its job).
>
> The task switching takes from 32 to 48 instruction cycles from the time
> one task calls 'Yeld' to the time the next task is running again (may
> take more for more complex tasks, with a lot of Yields, etc).
>
>
> It is implemented in C and compiles with Microchip MPLAB C30 (GCC). It
> doesn't use any 'dirty' tricks, so it should be easily ported to any
> processor architecture in existence for which there is a C compiler,
> even a PIC16F (for which the original version was written).
>
> It is a compromise between the flexibility offered by and the amount of
> RAM and CPU cycles wasted by a real preemptive RTOS. Comparing with
> FreeRTOS, it should be possible to run approximately five times more
> tasks with the same amount of RAM.
>
> For now it is already complete enough for real uses, supplying 'Yield',
> 'Delay' (sleep), 'CreateTask', 'DeleteTask', 'MutexTake', 'MutexGive'
> and 'ResumeTask'.
>
> In the future I will implement mailboxes and conditional yield (to yield
> only after the task has run for a minimum time) to reduce the number of
> unnecessary task switching.
>
> Tasks that are sleeping or are waiting for some object (a mutex, for
> instance) don't waste any CPU time until they are running again.
>
>
> I will be posting the code soon on www.piclist.com.
>
>
> Isaac
>
>

Sweet! This is going to be very useful for me.
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