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Software Interrupts

Thread Scheduling 4-29

2) To change the priority of a SWI object, drag the software interrupt to the

folder of the corresponding priority. For example, to change the priority of

SWI0 to 3, select it with the mouse and drag it to the folder labeled

Priority 3.

Software interrupts can have up to 15 priority levels. The highest level is

SWI_MAXPRI (14). The lowest is SWI_MINPRI (0). The priority level of

0 is reserved for the KNL_swi object, which runs the task scheduler. See

section 4.3.3, Software Interrupt Priorities and Application Stack Size,

page 4-29, for stack size restrictions. You cannot sort software interrupts

within a single priority level.

The Property window for an SWI object shows its numeric priority level (from

0 to 14; 14 is the highest level). You can also set the priority by selecting the

priority level from the menu in the Property window as shown in Figure 4-6.

Figure 4-6. SWI Properties Dialog Box

4.3.3 Software Interrupt Priorities and Application Stack Size

All threads in DSP/BIOS, excluding tasks, are executed using the same

system stack.

The system stack stores the register context when a software interrupt

preempts another thread. To allow the maximum number of preemptions that

can occur at run time, the required stack size grows each time you add a

software interrupt priority level. Thus, giving software interrupts the same

priority level is more efficient in terms of stack size than giving each software

interrupt a separate priority.

The default system stack size for the MEM module is 256 words. You can

change the sizes in the Configuration Tool. The estimated sizes required are

shown in the status bar at the top of the Configuration Tool.

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Coma FW-C2800 User's Guide Page 134