feat(shields): Add Zephirum.

app/boards/shields/zephirum/Kconfig.defconfig

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+# Copyright (c) 2021 The ZMK Contributors
+# SPDX-License-Identifier: MIT
+
+if SHIELD_ZEPHIRUM
+
+config ZMK_KEYBOARD_NAME
+	default "Zephirum"
+
+if ZMK_DISPLAY
+
+config I2C
+	default y
+
+config SSD1306
+	default y
+
+config SSD1306_REVERSE_MODE
+	default y
+
+endif # ZMK_DISPLAY
+
+if LVGL
+
+config LVGL_HOR_RES_MAX
+	default 128
+
+config LVGL_VER_RES_MAX
+	default 32
+
+config LVGL_VDB_SIZE
+	default 64
+
+config LVGL_DPI
+	default 148
+
+config LVGL_BITS_PER_PIXEL
+	default 1
+
+choice LVGL_COLOR_DEPTH
+	default LVGL_COLOR_DEPTH_1
+endchoice
+
+endif # LVGL
+
+endif

app/boards/shields/zephirum/Kconfig.shield

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+ #
+ # Copyright (c) 2021 The ZMK Contributors
+ #
+ # SPDX-License-Identifier: MIT
+ #
+
+config SHIELD_ZEPHIRUM
+	def_bool $(shields_list_contains,zephirum)

app/boards/shields/zephirum/README.md

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+# [Zephirum](http://zephirum.tuxfamily.org)
+
+## Description
+
+Despite having a look similar to many other ergo monoblock angled
+keyboards, this build has a couple of unique features:
+
+- it has been designed with [LibrePCB](https://librepcb.org/). This EDA
+  tool deserves more love, so I published the project & library files
+  under CC0 1.0 licence.
+
+- its MCU board is a Nucleo STM32WB55CG USB dongle (MB1293); it is
+  surface mounted on the top to showcase it ☺
+
+Regarding the other features, they are more classic:
+
+- it has been designed for Kailh Choc switches with MBK keycaps
+  (L=17.5mm × H=16.5mm)
+
+- it is powered by ZMK; only USB HID is supported so far.
+
+- it features an I²C 128x32 OLED screen (SSD1306)
+
+
+## Resources
+
+<https://git.tuxfamily.org/zephirum>

app/boards/shields/zephirum/zephirum.conf

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+# Uncomment the following line to enable OLED display.
+# CONFIG_ZMK_DISPLAY=y

app/boards/shields/zephirum/zephirum.keymap

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+/*
+ * Copyright (c) 2021 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <behaviors.dtsi>
+#include <dt-bindings/zmk/keys.h>
+#include <dt-bindings/zmk/bt.h>
+#include <dt-bindings/zmk/outputs.h>
+
+#define BASE        0
+#define SYMBOLS     1
+#define NUM_NAV     2
+
+#define COMPOSE CAPS
+
+/ {
+	keymap {
+		compatible = "zmk,keymap";
+
+		default_layer {
+			label ="Base";
+
+			bindings = <
+&sl COMPOSE &kp Q &kp W &kp E &kp R &kp T   &kp Y &kp U &kp I     &kp O   &kp P     &kp SQT
+&kp TAB     &kp A &kp S &kp D &kp F &kp G   &kp H &kp J &kp K     &kp L   &kp SEMI  &kp ENTER 
+&sk LGUI    &kp Z &kp X &kp C &kp V &kp B   &kp N &kp M &kp COMMA &kp DOT &kp SLASH &kp MINUS
+
+&sl SYMBOLS &kp BSPC &sk LCTRL &sl NUM_NAV
+&none       &sk LALT &kp SPACE &sk RSHIFT
+			>;
+		};
+
+		symbols_layer {
+			label ="Symbols";
+			bindings = <
+&kp ESC &none     &kp LT    &kp EQUAL &kp GT   &kp MINUS  &kp TILDE &kp LBKT  &kp UNDER &kp RBKT &none     &none
+&none   &kp HASH  &kp LPAR  &kp DLLR  &kp RPAR &kp EXCL	  &kp AT    &kp LBRC  &kp STAR  &kp RBRC &kp COLON &none 
+&trans  &kp CARET &kp PRCNT &kp PIPE  &kp BSLH &kp PLUS	  &kp AMPS  &kp GRAVE &kp DQT   &kp SQT  &kp QMARK &none 
+
+&trans      &kp DEL  &trans    &none
+&none       &trans   &none     &trans
+			>;
+		};
+
+		num_nav_layer {
+			label ="Num/Nav";
+			bindings = <
+
+&kp ESC &kp N1 &kp N2   &kp N3    &kp N4  &kp N5  &kp N6 &kp N7   &kp N8   &kp N9    &kp N0 &none
+&none   &none  &kp HOME &kp PG_UP &kp END &none   &none  &kp LEFT &kp UP   &kp RIGHT &none  &none
+&trans  &none  &none    &kp PG_DN &none   &none   &none  &none    &kp DOWN &none     &none  &none
+&none       &none    &trans    &trans
+&none       &trans   &none     &trans
+			>;
+		};
+	};
+};

app/boards/shields/zephirum/zephirum.overlay

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+/*
+ * Copyright (c) 2021 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <dt-bindings/zmk/matrix_transform.h>
+
+/ {
+	chosen {
+		zmk,kscan = &kscan;
+		zmk,matrix_transform = &default_transform;
+	};
+
+	default_transform: keymap_transform_0 {
+		compatible = "zmk,matrix-transform";
+		columns = <12>;
+		rows = <4>;
+		map = <
+RC(0,0) RC(0,1) RC(0,2) RC(0,3) RC(0,4) RC(0,5)   RC(3,5) RC(3,4) RC(3,3) RC(3,2) RC(3,1) RC(3,0)
+RC(1,0) RC(1,1) RC(1,2) RC(1,3) RC(1,4) RC(1,5)   RC(4,5) RC(4,4) RC(4,3) RC(4,2) RC(4,1) RC(4,0)
+RC(2,0) RC(2,1) RC(2,2) RC(2,3) RC(2,4) RC(2,5)   RC(5,5) RC(5,4) RC(5,3) RC(5,2) RC(5,1) RC(5,0)
+                RC(2,6) RC(6,0) RC(6,1) RC(6,2)   RC(6,3) RC(6,4) RC(6,5) RC(5,6)
+>;
+	};
+
+	kscan: kscan {
+		compatible = "zmk,kscan-gpio-matrix";
+		label = "KSCAN";
+		diode-direction = "col2row";
+
+		col-gpios = <&gpioa 5 GPIO_ACTIVE_HIGH>,
+		            <&gpioa 6 GPIO_ACTIVE_HIGH>,
+		            <&gpioa 7 GPIO_ACTIVE_HIGH>,
+		            <&gpioa 1 GPIO_ACTIVE_HIGH>,
+		            <&gpioa 8 GPIO_ACTIVE_HIGH>,
+		            <&gpioa 9 GPIO_ACTIVE_HIGH>,
+		            <&gpiob 2 GPIO_ACTIVE_HIGH>;
+
+		row-gpios = <&gpiob 6 (GPIO_ACTIVE_HIGH  | GPIO_PULL_DOWN)>,
+		            <&gpioa 3 (GPIO_ACTIVE_HIGH  | GPIO_PULL_DOWN)>,
+		            <&gpioa 2 (GPIO_ACTIVE_HIGH  | GPIO_PULL_DOWN)>,
+		            <&gpiob 3 (GPIO_ACTIVE_HIGH  | GPIO_PULL_DOWN)>,
+		            <&gpioa 14 (GPIO_ACTIVE_HIGH | GPIO_PULL_DOWN)>,
+		            <&gpioa 13 (GPIO_ACTIVE_HIGH | GPIO_PULL_DOWN)>,
+		            <&gpioa 0 (GPIO_ACTIVE_HIGH  | GPIO_PULL_DOWN)>;
+	};
+};
+
+&i2c1 {
+	status = "okay";
+
+	oled: ssd1306@3c {
+		compatible = "solomon,ssd1306fb";
+		reg = <0x3c>;
+		label = "DISPLAY";
+		width = <128>;
+		height = <32>;
+		segment-offset = <0>;
+		page-offset = <0>;
+		display-offset = <0>;
+		multiplex-ratio = <31>;
+		segment-remap;
+		com-invdir;
+		com-sequential;
+		prechargep = <0x22>;
+	};
+};

app/boards/shields/zephirum/zephirum.zmk.yml

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+file_format: "1"
+id: zephirum
+name: Zephirum
+type: shield
+url: http://zephirum.tuxfamily.org/
+requires: [nucleo_wb55cg_dongle]
+exposes: [i2c_oled]
+features:
+  - keys
+  - display