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# The Situation
In February 2016, Norman Davie released a program he called [Deeper Thought](https://groups.google.com/forum/#!msg/pidp-8/tbciVNoZJbw/AMjywRKLAwAJ) after an earlier program by Steve Gibson called [Deep Thought](https://www.grc.com/pdp-8/deepthought-sbc.htm). The most important difference between these two programs for our purposes here is that instead of running as PDP-8 code within the simulator, as Gibson's program does, Davie's Deeper Thought runs as a native program on the Raspberry Pi, using a version of Oscar Vermeulen's original `gpio.c` module to manipulate the LEDs on the PiDP-8/I's front panel and read its switches.
Davie's program has been [forked several times](https://github.com/timdawg/Deeper-Tought-2/network), but this mode of operation remains in all of the versions I've tried.
When Ian Schofield created the [incandescent lamp simulator](/wiki?name=Incandescent+Lamp+Simulator) (ILS) for the PiDP-8/I, he changed the external interface in a couple of ways which prevented it from being used with any of these versions of Deeper Thought.
When I rewrote the ILS, one of the things I did was add a compatibility interface for programs like Deeper Thought, which dependent on the old `gpio.c` module interface. This article describes the steps you must take to build a version of Deeper Thought against our new ILS.
When I rewrote the ILS, one of the things I did was add a compatibility interface for programs like Deeper Thought which remain dependent on the old `gpio.c` module interface. This article describes the steps you must take to build a version of Deeper Thought against our new ILS.
# Modifying `deeper.c`
The first thing you have to do to build any version of Deeper Thought against the current version of the PiDP-8/I software is copy its `deeper.c` file into the PiDP-8/I software's `src` subdirectory:
$ cd ~/pidp8i ⇠ or wherever the PiDP-8/I source code is
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