Task Switching in advanced microprocessor.pptx

In advanced processor task switching is required for multitasking operation.

1. Task Switching 80486

2. Invisible Registers

3. Task State Segment ( TSS ) Each task is assigned a Task State segment TSS contains- Registers and flag contents Selector for tasks LDT Link to TSS of prviously executing task ( Call / INT )

4. TSS

5. Task Switch Call / Jump Directly Point Indirectly Point via Task Gate INT Indirect via Task Gate IRET

6. Task Switch using TSS - direct CALL / JMP - FAR Segment --- Selector 2. CPL & RPL <= DP[L if no --- exception 3. Check if TSS is in memory if no loaded into memory by exception ISR 4. Copied Current Task's Register content to Current Tasks TSS 5. Load TR with selector & descriptor of new task TSS 6. Registeer values copied from TSS into registers 7.New task Begins.

7. Task Switch using TSS - indirect - Task Gate CALL / JMP - FAR Segment --- Selector 2. CPL & RPL <= DP[L if no --- exception 3. Task Gate Selector --- Descriptor 4. Check if TSS is in memory if no loaded into memory by exception ISR 5. Copies Current Task's Register content to Current Tasks TSS 6. Load TR with selector & descriptor of new task TSS 7. Registeer values copied from TSS into registers 8.New task Begins.