RTEMS Intel i960 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 thirty-one (31) 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 2.5 microseconds on a 33 Mhz i960CA with zero wait states. These numbers will vary based the number of wait states and processor speed present on the target board. [NOTE: This calculation was most recently 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 Intel i960 Applications Supplement
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