Method of task execution environment switch in multitask system

1 . A task execution environment switching method in a multitask system, comprising the steps of:

a first step for evacuating current task execution environment information of a task-exclusive-use execution environment stack to a context evacuating region, as pre-processing for calling processing of a sub-function from a main function within said task;

a second step for storing execution environment information of said sub-function in a execution environment stack for function of said task from an execution environment table of said task;

a third step for calling said sub-function from said main function within said task; and

a fourth step for storing said task execution environment information evacuated to said context evacuating region in said first step in a task of said task-exclusive-use execution environment stack, when processing is returned from said sub-function to said main function.

2 . The task execution environment switching method according to claim 1 , further comprising the steps of:

just before said second step, a step for transferring said task execution information in said execution environment table to an exclusive state to be used exclusively from other tasks; and

just after said fourth step, a step for releasing said exclusive state.

3 . The task execution environment switching method according to claim 2 , wherein:

in said first step, it is judged whether or not a flag is set for indicating that another task provided in each task execution environment information in said execution environment table is in use and, said task is shifted to a standby state in said first step when it is judged that said flag is being set;

when it is judged in said first step that said flag is not being set, said flag is set in said step for transferring to said exclusive state to transfer said task execution information in said execution environment table to said exclusive sate through setting said flag in said step for transferring to said exclusive state; and

said exclusive state is released by clearing said flag in said step for releasing said exclusive state.

4 . The task execution environment switching method according to claim 2 , wherein:

said step for making the transition to said exclusive state is executed by changing a task to a task dispatch inhibited state; and

said step for releasing said exclusive state is executed by changing a task to a task dispatch permitted state.

5 . The task execution environment switching method according to claim 2 , wherein:

said step for making the transition to said exclusive state is executed by changing a task to an interruption inhibited state; and

said step for releasing said exclusive state is executed by changing a task to an interruption permitted state.

6 . The task execution environment switching method according to claim 1 , wherein:

said task execution environment is a stack register; and

said task execution environment information is a stack region address used in said sub-function.

7 . The task execution environment switching method according to claim 1 , wherein said context evacuating region indicates a stack region address.