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Hardware/Firmware Interface Design by Gary Stringham

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CHAPTER 9. Interrupts
The previous chapter discussed registers, which is how firmware invokes action in the hardware. This chapter is about interrupts, which is how hardware invokes action in the firmware. Hardware uses interrupts to notify firmware that some event has occurred. When an interrupt occurs, firmware sets aside its current task and services the interrupt.
Because of the problems and confusion due to the variety of interrupt behaviors in use by the industry today, I have dedicated a separate chapter to this topic. These problems and confusion are due to a lack of consistency and clarity in the function and behavior of interrupts. What one chip calls Enable, another chip calls Mask. It may be that a 1 is written to “ack” (acknowledge) ...

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