GPIOIIC(4)

💅 GPIOIIC(4) 💅

okay bestie, so this one's a gpioiic man page — it's the GPIO I2C bit-banging device driver and honestly it's giving main character energy for your embedded projects ✨

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🎀 SYNOPSIS 🎀

so if you wanna bake this driver right into your kernel, drop these lines in your kernel configuration file fr fr:

device gpio
device gpioiic
device iicbb
device iicbus

or, if you'd rather just load it as a module at boot time (lowkey the easier vibe), put this line in loader.conf(5):

gpioiic_load="YES"

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✨ DESCRIPTION ✨

okay so the gpioiic driver is out here giving you an IIC bit-banging interface using just two GPIO pins for the SCL and SDA lines on the bus. iconic behavior honestly 🦋

here's the tea though: gpioiic simulates an open collector kind of output when it's managing the pins on the bus — even on systems that don't directly support configuring gpio pins in that mode. and like, it's very mindful about it: the pins are never driven to the logical value of '1'. nope. they get driven to '0' or switched to input mode (Hi-Z/tri-state), and then an external pullup resistor pulls the line to the 1 state — unless some other device on the bus is out here driving it to 0. teamwork makes the dream work 💖

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🌸 HINTS CONFIGURATION 🌸

on a device.hints(5) based system (like MIPS), these values are configurable for gpioiic:

• hint.gpioiic.%d.at — the gpiobus you're attaching to. normally it's just gpiobus0 on systems with a single bank of gpio pins.
• hint.gpioiic.%d.pins — this is a bitmask of the pins on the gpiobus that get used for SCLOCK and SDATA from the GPIO IIC bit-banging bus. so to configure pin 0 and 7, you use the bitmask of 0b10000001 and convert it to a hexadecimal value of 0x0081. also ⚠️ please note this mask should only ever have two bits set (any other bits — i.e. pins — will just be ignored). and because gpioiic must be a child of the gpiobus, both gpio pins must be part of that bus. no exceptions bestie.
• hint.gpioiic.%d.scl — indicates which bit in the hint.gpioiic.%d.pins should be used as the SCLOCK source. it's optional and defaults to 0.
• hint.gpioiic.%d.sda — indicates which bit in the hint.gpioiic.%d.pins should be used as the SDATA source. also optional, defaults to 1.

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🦋 FDT CONFIGURATION 🦋

on an FDT(4) based system (like ARM), the DTS node for gpioiic conforms to the standard bindings document i2c/i2c-gpio.yaml. the device node typically appears at the root of the device tree. here's an example of a gpioiic node with one slave device on the IIC bus:

/ {
        gpioiic0 {
                compatible = "i2c-gpio";
                pinctrl-names = "default";
                pinctrl-0 = <&pinctrl_gpioiic0>;
                scl-gpios = <&gpio1  5 GPIO_ACTIVE_HIGH>;
                sda-gpios = <&gpio7 11 GPIO_ACTIVE_HIGH>;
                status = "okay";

                /* One slave device on the i2c bus. */
                rtc@51 {
                        compatible="nxp,pcf2127";
                        reg = <0x51>;
                        status = "okay";
                };
        };
};

so what's what:

• compatible — should be set to "i2c-gpio". but heads up: the deprecated string "gpioiic" is also accepted for backwards compatibility. we love a nostalgic moment 💀
• scl-gpios / sda-gpios — these properties indicate which GPIO pins should be used for clock and data on the GPIO IIC bit-banging bus. and like, there's no requirement that the two pins belong to the same gpio controller. they can be from totally different friend groups, it's fine 🫶
• pinctrl-names / pinctrl-0 — these properties may be required to configure the chosen pins as gpio pins, unless the pins already default to that state on your system. iykyk.

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💜 SEE ALSO 💜

fdt(4), gpio(4), iic(4), iicbb(4), iicbus(4)

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⭐ HISTORY ⭐

the gpioiic manual page first appeared in FreeBSD 10.1. a whole era 💅

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👑 AUTHORS 👑

this manual page was written by Luiz Otavio O Souza. respect the icon who wrote it 🙌

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alright bestie, that's the whole page! this version is from Debian, dated December 1, 2019 — and honestly the Debian folks ate with this one. now go forth and bit-bang responsibly 🧚✨