emWin - SEGGER Microcontroller

314 CHAPTER Execution Model: Single Task / Multitask
14.1 Supported execution models
We have to basically distinguish between 3 different execution models:
Single task system (superloop)
The entire program runs in one superloop. Normally, all software components are
periodically called. Interrupts must be used for real time parts of the software since
no real time kernel is used.
Multitask system: one task calling emWin
A real time kernel (RTOS) is used, but only one task calls emWin functions. From the
graphic software’s point of view, it is the same as being used in a single task system.
Multitask system: multiple tasks calling emWin
A real time kernel (RTOS) is used, and multiple tasks call emWin functions. This
works without a problem as long as the software is made thread-safe, which is done
by enabling multitask support in the configuration and adapting the kernel interface
routines. For popular kernels, the kernel interface routines are readily available.
14.2 Single task system (superloop)
14.2.1 Description
The entire program runs in one superloop. Normally, all components of the software
are periodically called. No real time kernel is used, so interrupts must be used for
real time parts of the software. This type of system is primarily used in smaller systems
or if real time behavior is not critical.
14.2.2 Superloop example (without emWin)
void main (void) {
HARDWARE_Init();
}
/* Init software components */
XXX_Init();
YYY_Init();
/* Superloop: call all software components regularily */
while (1) {
/* Exec all compontents of the software */
XXX_Exec();
YYY_Exec();
}
14.2.3 Advantages
No real time kernel is used (-> smaller ROM size, just one stack -> less RAM for
stacks), no preemption/synchronization problems.
14.2.4 Disadvantages
The superloop type of program can become hard to maintain if it exceeds a certain
program size. Real time behavior is poor, since one software component cannot be
interrupted by any other component (only by interrupts). This means that the reaction
time of one software component depends on the execution time of all other components
in the system.
14.2.5 Using emWin
There are no real restrictions regarding the use of emWin. As always, GUI_Init()
has to be called before you can use the software. From there on, any API function
can be used. If the Window Manager’s callback mechanism is used, then an emWin
update function has to be called regularly. This is typically done by calling the
UM03001 User & Reference Guide for emWin V5.18 © 1997 - 2012 SEGGER Microcontroller GmbH & Co. KG