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David Howells authored
Make the FRV arch use virtual interrupt disablement because accesses to the processor status register (PSR) are relatively slow and because we will soon have the need to deal with multiple interrupt controls at the same time (separate h/w and inter-core interrupts). The way this is done is to dedicate one of the four integer condition code registers (ICC2) to maintaining a virtual interrupt disablement state whilst inside the kernel. This uses the ICC2.Z flag (Zero) to indicate whether the interrupts are virtually disabled and the ICC2.C flag (Carry) to indicate whether the interrupts are physically disabled. ICC2.Z is set to indicate interrupts are virtually disabled. ICC2.C is set to indicate interrupts are physically enabled. Under normal running conditions Z==0 and C==1. Disabling interrupts with local_irq_disable() doesn't then actually physically disable interrupts - it merely sets ICC2.Z to 1. Should an interrupt then happen, the exception prolo...
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