Renesas 70 - Manual (Page 150)

Chapter 7 Application Creation Guide
- 140 -
7.2 Stacks
7.2.1 System Stack and User Stack
The MR308 provides two types of stacks: system stack and user stack.
•
User Stack
One user stack is provided for each task. Therefore, when writing applications with the MR308, it is
necessary to furnish the stack area for each task.
•
System Stack
This stack is used within the MR308 (during service call processing). When a service call is issued
from a task, the MR308 switches the stack from the user stack to the system stack (See Figure 7.4).
The system stack use the interrupt stack(ISP).
Task MR308 system call processing
User Stack
User Stack
System Stack
Save Registers
Stack switching
System call
processing
Task selection
Stack switching
Restore Registers
XXX_XXX( )
Figure 7.4 System Stack and User Stack
Switchover from user stack to system stack occurs when an interrupt of vector numbers 0 to 31 or 247 to 255 is
generated. Consequently, all stacks used by the interrupt handler are the system stack.