RTEMS Motorola MC68xxx Applications Supplement
During the execution of directive calls, critical sections of code may be executed. When these sections are encountered, RTEMS disables interrupts to level seven (7) before the execution of this section and restores them to the previous level upon completion of the section. RTEMS has been optimized to insure that interrupts are disabled for less than TBD microseconds on a 20 Mhz MC68020 with zero wait states. These numbers will vary based the number of wait states and processor speed present on the target board. [NOTE: The maximum period with interrupts disabled is hand calculated. This calculation was last performed for Release 3.2.1.]
Non-maskable interrupts (NMI) cannot be disabled, and ISRs which execute at this level MUST NEVER issue RTEMS system calls. If a directive is invoked, unpredictable results may occur due to the inability of RTEMS to protect its critical sections. However, ISRs that make no system calls may safely execute as non-maskable interrupts.
RTEMS Motorola MC68xxx Applications Supplement
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