MCP23S17 software interrupt ideas

Now that RPi recognizes the MCP23S17 and also drives GA0, GB0's LEDs, I have confidence to move on.  I have now completed the point ot point soldering of the remaining GAx, GBx pins, and also Reset, IntA and IntB.

At first I thought that this IOx is all O and no I, so there is no use for interrupt pin.  On second thought, I might make use of the IOx chip's interrupt on change thing to trigger interrupt when 1 of the 16 pins changed value by software.  But I am not sure if this makes any sense.

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