Christian Werner
b2e4f9710d
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Adopt the confirmed-working reference's pin assignment so the module runs on that proven wiring: DATA=BCM2 (pin 3), CLK=BCM3 (pin 5), ATN=BCM4 (pin 7). RESET is kept and relocated to BCM17 (pin 11), the pin freed by moving CLK. All five GPIOs stay in bank 0, so the direct-register hot path and ATN IRQ are unchanged -- only the IEC_GPIO_* defines, the device-tree overlay, and the docs/self-test move. DATA/CLK now sit on the ARM I2C pins (GPIO2/3) with the SoC's fixed ~1.8k pull-ups; keep dtparam=i2c_arm off. The bare-board self-test expectation changes from 0x15 to 0x0b accordingly. Generated by Clanker
45 lines
1.5 KiB
Plaintext
45 lines
1.5 KiB
Plaintext
/*
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* iec-overlay.dts - pin reservation + pull configuration for the IEC listener.
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*
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* GPIO 4 = ATN (input, pull-up: bus idle = 5 V = high)
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* GPIO 3 = CLK (input, pull-up)
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* GPIO 17 = RESET (input, pull-up)
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* GPIO 2 = DATA (bidirectional; starts as input/Hi-Z, the module flips it)
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*
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* NOTE: DATA (GPIO2) and CLK (GPIO3) are the ARM I2C pins and carry the SoC's
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* fixed ~1.8 kOhm pull-ups, which the overlay's pull settings cannot fully
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* override. Benign here (DATA is open-drain). Keep dtparam=i2c_arm OFF so I2C
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* does not claim these pins.
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*
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* The module drives GPIO via direct registers, so this overlay's main job is to
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* reserve the pins and set sane pull defaults. Build & install:
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* dtc -@ -I dts -O dtb -o iec-overlay.dtbo iec-overlay.dts
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* sudo cp iec-overlay.dtbo /boot/firmware/overlays/ # Bookworm path
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* echo "dtoverlay=iec-overlay" | sudo tee -a /boot/firmware/config.txt
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* # reboot, then: dtoverlay -l
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*
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* See _research/pi-kernel-module-rt-gpio-2026-06-18.md §4.1.
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*/
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/dts-v1/;
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/plugin/;
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/ {
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compatible = "brcm,bcm2837";
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fragment@0 {
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target = <&gpio>;
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__overlay__ {
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iec_input_pins: iec_input_pins {
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brcm,pins = <4 3 17>; /* ATN, CLK, RESET */
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brcm,function = <0>; /* 0 = input */
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brcm,pull = <2>; /* 2 = pull-up */
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};
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iec_data_pin: iec_data_pin {
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brcm,pins = <2>; /* DATA */
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brcm,function = <0>; /* start as input (Hi-Z) */
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brcm,pull = <0>; /* 0 = none (shifter drives) */
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};
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};
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};
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};
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