For tweaking the amount of code executed in each state machine, it can=20
be useful to use a D/A converter, or a few (3) bits driving an R2R=20
ladder.  Say you have 5 tasks in your main loop:


int main() {
     // initialize stuff...
     while(1) {
         one_machine();
         two_machine();
         ...
         five_machine();
}

You can assign each machine an int value, and start each machine's=20
routine with an assignment of it's value to the D/A or R2R port. You can=20
watch the D/A or R2R with a scope, and learn how the work is being=20
distributed among the machines, and adjust code based on that.

#define ONE_VALUE 1
one_machine() {
         r2r_port =3D ONE_VALUE;
         // work...
}

I don't recall where I first heard of it, but I've used it and it was=20
useful.  If focusing on a single machine, you can use the same technique=20
for each state in the machine.

Joe W


On 4/19/2013 3:23 AM, Veronica Merryfield wrote:
> I have used a state machine based co-operative multitasking approach in m=
any systems. The main code is a loop calling each task state machine, which=
 is a large switch statement, usually. Finding the right size of block and =
unrolling loops can get tedious and it can look messy but it does work well=
.. I have had such systems deal with timers and comms, the interrupt handles=
 just raise flags and the code in the state machines handles things.
>
> On 2013-04-18, at 11:20 PM, veegee <veegee@veegee.org> wrote:
>
>> On 2013-04-18 10:59 AM, Joe Wronski wrote:
>>> Having never worked with any RTOS due to ROM and RAM limitations, I fin=
d
>>> Protothreads fascinating.    Where my cow-orkers and I had hand crafted
>>> state machines which closely resembled the Protothreads expanded macros=
,
>>> using PT would have made the code more readable and maintainable.  I ha=
d
>>> never considered using the __LINE__ macro for anything other than
>>> compiler error and warning info.  And I never realized that you could
>>> put the case : argument of a switch within a while loop (Duff's Device)=
..
>> Yup, C switches behave somewhat like labels. The cases are valid
>> anywhere within the switch.
>>
>> --=20
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