/*
 * iec-overlay.dts - pin reservation + pull configuration for the IEC listener.
 *
 * GPIO 2  = ATN   (input,  pull-up: bus idle = 5 V = high)
 * GPIO 17 = CLK   (input,  pull-up)
 * GPIO 3  = RESET (input,  pull-up)
 * GPIO 18 = DATA  (bidirectional; starts as input/Hi-Z, the module flips it)
 *
 * The module drives GPIO via direct registers, so this overlay's main job is to
 * reserve the pins and set sane pull defaults. Build & install:
 *     dtc -@ -I dts -O dtb -o iec-overlay.dtbo iec-overlay.dts
 *     sudo cp iec-overlay.dtbo /boot/firmware/overlays/   # Bookworm path
 *     echo "dtoverlay=iec-overlay" | sudo tee -a /boot/firmware/config.txt
 *     # reboot, then: dtoverlay -l
 *
 * See _research/pi-kernel-module-rt-gpio-2026-06-18.md §4.1.
 */
/dts-v1/;
/plugin/;

/ {
	compatible = "brcm,bcm2837";

	fragment@0 {
		target = <&gpio>;
		__overlay__ {
			iec_input_pins: iec_input_pins {
				brcm,pins = <2 17 3>;   /* ATN, CLK, RESET */
				brcm,function = <0>;    /* 0 = input        */
				brcm,pull = <2>;        /* 2 = pull-up      */
			};
			iec_data_pin: iec_data_pin {
				brcm,pins = <18>;       /* DATA             */
				brcm,function = <0>;    /* start as input (Hi-Z) */
				brcm,pull = <0>;        /* 0 = none (shifter drives) */
			};
		};
	};
};