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3.5.2 Dispatch Enabled/Disabled States
The system assumes either a dispatch enabled state or a dispatch disabled state. In a dispatch disabled state, no task sched-
uling is performed. Nor can service calls be invoked that may cause the service call issuing task to enter a wait state.
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The system can be placed into a dispatch disabled state or a dispatch enabled state by the dis_dsp or ena_dsp service call,
respectively. Whether the system is in a dispatch disabled state can be known by the sns_dsp service call.
3.5.3 CPU Locked/Unlocked States
The system assumes either a CPU locked state or a CPU unlocked state. In a CPU locked state, all external interrupts are
disabled against acceptance, and task scheduling is not performed either.
The system can be placed into a CPU locked state or a CPU unlocked state by the loc_cpu(iloc_cpu) or unl_cpu(iunl_cpu)
service call, respectively. Whether the system is in a CPU locked state can be known by the sns_loc service call.
The service calls that can be issued from a CPU locked state are limited to those that are listed in Table 3-2.
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Table 3.2 Invocable Service Calls in a CPU Locked State
loc_cpu iloc_cpu unl_cpu iunl_cpu
ext_tsk exd_tsk sns_tex sns_ctx
sns_loc sns_dsp sns_dpn
3.5.4 Dispatch Disabled and CPU Locked States
In µITRON 4.0 Specification, the dispatch disabled and the CPU locked states are clearly discriminated. Therefore, if the
unl_cpu service call is issued in a dispatch disabled state, the dispatch disabled state remains intact and no task scheduling
is performed. State transitions are summarized in Table 3.3.
T
able 3.3 CPU Locked and Dispatch Disabled State Transitions Relating to dis_dsp and loc_cpu
Content of state
State
number
CPU locked
state
Dispatch disabled
state
dis_dsp
executed
ena_dsp
executed
loc_cpu
executed
unl_cpu
executed
1 O X X X => 1 => 3
2 O O X X => 2 => 4
3 X X => 4 => 3 => 1 => 3
4 X O => 4 => 3 => 2 => 4
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If a service call not issuable is issued when dispatch disabled, MR100 doesn't return the error and doesn't guarantee the operation.
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MR100 does not return an error even when an uninvocable service call is issued from a CPU locked state, in which case, however, its
operation cannot be guaranteed.