The interrupt detection logic monitors the GPIO input signal. The interrupt trigger can be a positive edge, negative edge, either edge, Low-level or High-level. The trigger sensitivity is programmed using the INT_TYPE, INT_POLARITY and INT_ANY registers.
If an interrupt is detected, the GPIO's INT_STAT state is set true by the interrupt detection logic. If the INT_STAT state is enabled (unmasked), then the interrupt propagates through to a large OR function. This function combines all interrupts for all GPIOs in all four banks to one output (IRQ ID#52) to the interrupt controller. If the interrupt is disabled (masked), then the INT_STAT state is maintained until cleared, but it does not propagate to the interrupt controller unless the INT_EN is later written to disable the mask. As all GPIOs share the same interrupt, software must consider both INT_MASK and INT_STAT to determine which GPIO is causing an interrupt.
The interrupt mask state is controlled by writing a 1 to the INT_EN and INT_DIS registers. Writing a 1 to the INT_EN register disables the mask allowing an active interrupt to propagate to the interrupt controller. Writing a 1 to the INT_DIS register enables the mask. The state of the interrupt mask can be read using the INT_MASK register.
If the GPIO interrupt is edge sensitive, then the INT state is latched by the detection logic. The INT latch is cleared by writing a 1 to the INT_STAT register. For level-sensitive interrupts, the source of the interrupt input to the GPIO must be cleared in order to clear the interrupt signal. Alternatively, software can mask that input using the INT_DIS register.
The state of the interrupt signal going to the interrupt controller can be inferred by reading the INT_STAT and INT_MASK registers. This interrupt signal is asserted if INT_STAT=1 and INT_MASK=0.
GPIO bank control is summarized as follows:
•INT_MASK: This register is read-only and shows which bits are currently masked and which are un-masked/enabled.
•INT_EN: Writing a 1 to any bit of this register enables/unmasks that signal for interrupts. Reading from this register returns an unpredictable value.
•INT_DIS: Writing a 1 to any bit of this register masks that signal for interrupts. Reading from this register returns an unpredictable value.
•INT_STAT: This registers shows if an interrupt event has occurred or not. Writing a 1 to a bit in this register clears the interrupt status for that bit. Writing a 0 to a bit in this register is ignored.
•INT_TYPE: This register controls whether the interrupt is edge sensitive or level sensitive.
•INT_POLARITY: This register controls whether the interrupt is active-Low or active High (or falling-edge sensitive or rising-edge sensitive).
•INT_ON_ANY: If INT_TYPE is set to edge sensitive, then this register enables an interrupt event on both rising and falling edges. This register is ignored if INT_TYPE is set to level sensitive.