cpu_check_irqs
- handle SOFTINT register TICK and STICK timer bits
- only check interrupt levels greater than PIL value
- handle preemption by higher level traps
cpu_exec
- handle CPU_INTERRUPT_HARD only if interrupts are enabled
- PIL 15 is not special level on sparcv9
Signed-off-by: Igor V. Kovalenko <igor.v.kovalenko@gmail.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
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