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powerbread: new breadboard power monitor app (QT Py ESP32-C3) (#53)
* docs: add powerbread app design spec * docs: add powerbread implementation plan * powerbread: scaffold new app (QT Py ESP32-C3) * powerbread: add INA3221 sampler (100 Hz, stats, energy, chart ring) * docs: powerbread plan — fix fmt sign-loss and app_version include path * powerbread: fix CSV sign loss for small negative values * powerbread: add shell commands (read, reset, stream) * powerbread: add ST7735 display and LVGL dashboard * powerbread: add chart and stats screens * powerbread: add dial wheel input and mode/channel/dial shell commands * powerbread: avoid re-running ADC channel setup in dial command * powerbread: add README with wiring and usage * powerbread: drop unused pb_ui_get_mode, include errno.h explicitly * powerbread: hardware bring-up fixes, UI restyle, native_sim target
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‎applications/powerbread/CMakeLists.txt‎

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cmake_minimum_required(VERSION 3.20.0)
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find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
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project(powerbread)
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target_sources(app PRIVATE
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src/main.c
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src/sampler.c
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src/shell.c
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src/ui.c
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src/input.c
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)

‎applications/powerbread/Kconfig‎

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mainmenu "Application options"
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source "Kconfig.zephyr"

‎applications/powerbread/README.md‎

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# PowerBread
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Dual-channel breadboard power monitor on the Adafruit QT Py ESP32-C3, ported
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from [XIAO-powerbread](https://github.com/nicho810/XIAO-powerbread): an
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INA3221 measures voltage/current/power on two supply rails, a 0.96" ST7735
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LCD shows an LVGL UI (dashboard, line chart, statistics), and a resistor-ladder
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dial wheel navigates it. Measurements stream as CSV over USB serial on demand.
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## Wiring
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| Function | QT Py pin | GPIO | Notes |
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|-------------------|-----------|--------|--------------------------------|
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| INA3221 SDA/SCL | SDA/SCL | 5 / 6 | Stemma QT, addr 0x40, 50 mR shunts |
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| LCD DIN (MOSI) | MO | 7 | SPI2 |
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| LCD CLK | SCK | 10 | SPI2 |
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| LCD DC | MI | 8 | re-pinmuxed from SPI2 MISO |
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| LCD RST | A3 | 0 | |
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| LCD CS | — | — | tied low on the module |
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| Dial wheel ladder | A2 / D2 | 1 | ADC1 channel 1 |
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## Controls
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- Dial up/down: cycle mode (dashboard → chart → stats)
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- Dial short press: switch focused channel (1 ↔ 2)
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- Dial long press (≥1 s): reset stats and energy counters
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Shell (USB serial), root command `powerbread`:
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`read`, `reset`, `stream <on|off>` (CSV: `t_ms,ch,mV,mA,mW`),
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`mode <dash|chart|stats>`, `channel <1|2>`, `dial` (raw dial mV, for
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calibrating the `adc-keys` thresholds in the board overlay).
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## Build & flash
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uv run poe app powerbread
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uv run poe flash powerbread
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## Simulator
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The UI runs on the host with synthetic sensor data (SDL window, no
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hardware needed) — useful for iterating on screens:
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uv run poe app powerbread --board native_sim/native/64
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./builds/powerbread/zephyr/zephyr.exe -rt

‎applications/powerbread/VERSION‎

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VERSION_MAJOR = 1
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VERSION_MINOR = 0
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PATCHLEVEL = 0
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VERSION_TWEAK = 0
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EXTRAVERSION =

‎applications/powerbread/boards/adafruit_qt_py_esp32c3.overlay‎

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/*
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* Copyright (c) 2026 Richard Osterloh
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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#include <zephyr/dt-bindings/adc/adc.h>
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#include <zephyr/dt-bindings/input/input-event-codes.h>
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&i2c0 {
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status = "okay";
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ina3221: ina3221@40 {
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compatible = "ti,ina3221";
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reg = <0x40>;
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/* PowerBread schematic: 50 mOhm shunts on channels 1+2 */
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shunt-resistors = <50 50 50>;
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enable-channel = <1 1 0>;
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/* 140 us conversions, x4 averaging: full 2-ch cycle ~2.24 ms */
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conv-time-shunt = <0>;
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conv-time-bus = <0>;
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avg-mode = <1>;
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};
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};
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/*
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* ST7735 0.96" 80x160 LCD, wired per the XIAO PowerBread schematic:
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* DIN=GPIO7 (SPI2 MOSI), CLK=GPIO10 (SPI2 SCLK), DC=GPIO8, RST=GPIO0,
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* CS tied low on the module (no CS GPIO), backlight hardwired on.
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* GPIO8 is SPIM2_MISO on the base board; re-pinmux SPI2 without MISO so
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* GPIO8 is free to drive the DC line (display is write-only).
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*/
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&pinctrl {
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spim2_lcd: spim2_lcd {
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group1 {
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pinmux = <SPIM2_SCLK_GPIO10>;
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};
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group2 {
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pinmux = <SPIM2_MOSI_GPIO7>;
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output-low;
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};
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};
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};
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&spi2 {
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pinctrl-0 = <&spim2_lcd>;
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pinctrl-names = "default";
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};
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/ {
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chosen {
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zephyr,display = &st7735r;
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};
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mipi_dbi {
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compatible = "zephyr,mipi-dbi-spi";
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spi-dev = <&spi2>;
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dc-gpios = <&gpio0 8 GPIO_ACTIVE_HIGH>;
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reset-gpios = <&gpio0 0 GPIO_ACTIVE_LOW>;
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write-only;
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#address-cells = <1>;
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#size-cells = <0>;
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/* Panel init values from the in-tree heltec_wireless_tracker
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* (same 0.96" 160x80 ST7735 panel), rotated to portrait.
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*/
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st7735r: st7735r@0 {
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compatible = "sitronix,st7735r";
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reg = <0>;
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mipi-max-frequency = <20000000>;
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mipi-mode = "MIPI_DBI_MODE_SPI_4WIRE";
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width = <80>;
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height = <160>;
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/* Match upstream LGFX_096_XPB: invert=false, offset 24/0,
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* rotation 0 (no MX/MY), BGR color order.
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*/
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x-offset = <24>;
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y-offset = <0>;
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madctl = <0x00>;
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colmod = <0x05>;
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invctr = <7>;
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vmctr1 = <0x0e>;
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pwctr1 = [a2 02 84];
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pwctr2 = [c1];
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pwctr3 = [0a 00];
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pwctr4 = [8a 2a];
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pwctr5 = [8a ee];
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frmctr1 = [01 26 2e];
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frmctr2 = [01 26 2e];
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frmctr3 = [01 26 2e 01 26 2e];
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gamctrp1 = [0f 1a 0f 18 2f 28 20 22 1f 1b 23 37 00 07 02 10];
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gamctrn1 = [0f 1b 0f 17 33 2c 29 2e 30 2e 30 3b 00 07 03 10];
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};
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};
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};
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/*
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* PowerBread dial wheel: resistor ladder on D2/A2 = GPIO1 = ADC1 channel 1.
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* Idle sits near 0 V; press/down/up produce distinct levels. Thresholds
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* derived from upstream's 10-bit values (XIAO ESP32-C3 build); calibrate
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* with `powerbread dial` and adjust here if the module differs.
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*/
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&adc0 {
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status = "okay";
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#address-cells = <1>;
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#size-cells = <0>;
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channel@1 {
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reg = <1>;
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zephyr,gain = "ADC_GAIN_1_4";
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zephyr,reference = "ADC_REF_INTERNAL";
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zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
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zephyr,resolution = <12>;
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};
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};
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/ {
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dial: dial {
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compatible = "adc-keys";
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io-channels = <&adc0 1>;
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keyup-threshold-mv = <0>;
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sample-period-ms = <20>;
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dial_press {
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press-thresholds-mv = <510>;
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zephyr,code = <INPUT_KEY_ENTER>;
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};
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dial_down {
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press-thresholds-mv = <910>;
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zephyr,code = <INPUT_KEY_DOWN>;
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};
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dial_up {
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press-thresholds-mv = <1580>;
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zephyr,code = <INPUT_KEY_UP>;
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};
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};
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longpress {
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compatible = "zephyr,input-longpress";
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input = <&dial>;
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input-codes = <INPUT_KEY_ENTER>;
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short-codes = <INPUT_KEY_A>;
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long-codes = <INPUT_KEY_B>;
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long-delay-ms = <1000>;
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};
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};

‎applications/powerbread/boards/native_sim_native_64.conf‎

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# native_sim: no I2C sensor or ADC dial hardware
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CONFIG_I2C=n
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CONFIG_SENSOR=n
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CONFIG_ADC=n

‎applications/powerbread/boards/native_sim_native_64.overlay‎

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/*
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* Copyright (c) 2026 Richard Osterloh
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*
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* SPDX-License-Identifier: Apache-2.0
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*
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* native_sim: SDL window stands in for the ST7735 (80x160); no INA3221 or
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* dial hardware — the sampler falls back to synthetic data.
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*/
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&sdl_dc {
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width = <80>;
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height = <160>;
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};

‎applications/powerbread/prj.conf‎

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# Logging. CSV streaming printk must NOT be routed through the deferred
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# log core: packaging ~200 printk/s with %s args crashes the logging
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# thread (illegal instruction, mepc=0). With LOG_PRINTK=n printk writes
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# synchronously to the console from the sampler thread instead.
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CONFIG_LOG=y
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CONFIG_LOG_PRINTK=n
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# Shell over USB serial (board chosen: zephyr,shell-uart = &usb_serial)
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CONFIG_SHELL=y
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CONFIG_MAIN_STACK_SIZE=8192
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# INA3221 current/voltage monitor
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CONFIG_I2C=y
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CONFIG_SENSOR=y
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# ST7735 display via MIPI-DBI SPI
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CONFIG_SPI=y
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CONFIG_MIPI_DBI=y
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CONFIG_DISPLAY=y
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# LVGL
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CONFIG_LVGL=y
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CONFIG_LV_COLOR_DEPTH_16=y
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CONFIG_LV_Z_MEM_POOL_SIZE=49152
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CONFIG_LV_Z_VDB_SIZE=100
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CONFIG_LV_USE_CHART=y
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CONFIG_LV_FONT_MONTSERRAT_12=y
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CONFIG_LV_FONT_MONTSERRAT_16=y
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CONFIG_LV_FONT_DEFAULT_MONTSERRAT_12=y
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# Dial wheel (adc-keys resistor ladder + longpress)
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CONFIG_ADC=y
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CONFIG_INPUT=y

‎applications/powerbread/src/input.c‎

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/*
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* Copyright (c) 2026 Richard Osterloh
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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#include "sampler.h"
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#include "ui.h"
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#include <zephyr/input/input.h>
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static void dial_cb(struct input_event *evt, void *user_data)
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{
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ARG_UNUSED(user_data);
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if (evt->type != INPUT_EV_KEY || evt->value != 1) {
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return;
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}
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switch (evt->code) {
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case INPUT_KEY_UP:
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pb_ui_step_mode(1);
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break;
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case INPUT_KEY_DOWN:
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pb_ui_step_mode(-1);
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break;
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case INPUT_KEY_A: /* dial short press */
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pb_ui_set_channel((pb_ui_get_channel() + 1) % PB_NUM_CH);
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break;
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case INPUT_KEY_B: /* dial long press */
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sampler_reset_stats();
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break;
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default:
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break;
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}
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}
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INPUT_CALLBACK_DEFINE(NULL, dial_cb, NULL);

‎applications/powerbread/src/main.c‎

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/*
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* Copyright (c) 2026 Richard Osterloh
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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#include "ui.h"
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#include <lvgl.h>
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#include <zephyr/kernel.h>
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#include <zephyr/logging/log.h>
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#include <zephyr/app_version.h>
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LOG_MODULE_REGISTER(main, LOG_LEVEL_INF);
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#define REFRESH_LOOP_CAP_MS 50
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int main(void)
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{
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LOG_INF("PowerBread %s", APP_VERSION_STRING);
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if (pb_ui_init() != 0) {
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LOG_ERR("UI disabled; sampler and shell remain active");
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k_sleep(K_FOREVER);
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}
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while (true) {
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uint32_t delay = lv_timer_handler();
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k_msleep(MIN(delay, REFRESH_LOOP_CAP_MS));
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}
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return 0;
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}

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