MoWatch App Development Skill

Use this skill when developing watch faces or apps for MoWatch e-ink smartwatch.

SDK Files Location

IMPORTANT: SDK source files are located in this skill's directory. Copy them to create a new project:

code

~/.claude/skills/mowatch-dev/
├── sdk/
│   ├── include/header.h       # SDK header - copy to include/
│   └── libs/
│       ├── init_datas.c       # API wrappers - copy to libs/
│       └── syscall_gcc.txt    # Syscall addresses - copy to libs/
└── templates/
    ├── Makefile               # Build config - copy to gcc/
    ├── app.ld                 # Linker script - copy to gcc/
    └── createmwa.py           # Package creator - copy to gcc/

To create a new project, read and copy these files using the Read tool.

Hardware Specifications

•Display: 200x200 pixel monochrome e-ink
•MCU: ARM Cortex-M3
•Colors: Black and white only (1-bit)
•Update: Partial refresh supported, full refresh every 5 minutes recommended

Memory Constraints (IMPORTANT!)

FLASH (rx)  : ORIGIN = 0x10050000, LENGTH = 40K   // Code + constants
RAM (xrw)   : ORIGIN = 0x11001000, LENGTH = 4K    // Variables only!

Only 4K RAM available! Keep global variables minimal. Use const for bitmap data.

Constants

#define SCREEN_WIDTH   200
#define SCREEN_HEIGHT  200

#define BLACK   0
#define WHITE   0xFF
#define GREY    0x80

#define MODE_EMPTY  0    // Rectangle outline
#define MODE_FILL   1    // Filled rectangle

// File access flags
#define FA_READ           0x01
#define FA_WRITE          0x02
#define FA_OPEN_EXISTING  0x00
#define FA_CREATE_NEW     0x04
#define FA_CREATE_ALWAYS  0x08
#define FA_OPEN_ALWAYS    0x10
#define FA_OPEN_APPEND    0x30

Enums and Data Structures

Update Types

typedef enum UPDAT_TYPE {
    FULL_UPDATE,    // Full screen refresh (prevents ghosting)
    PART_UPDATE,    // Partial refresh (faster but may ghost)
    NONE_UPDATE,    // No screen update
} UpdateType;

Button Types

typedef enum MBUTTON_TYPE {
    KEY_NULL,
    KEY_CENTER,       // Center button press
    KEY_UP,           // Up button press
    KEY_DOWN,         // Down button press
    KEY_CENTER_UP,    // Center then Up
    KEY_UP_CENTER,    // Up then Center
    KEY_CENTER_DOWN,  // Center then Down
    KEY_DOWN_CENTER,  // Down then Center
    KEY_UP_DOWN,      // Up then Down
    KEY_DOWN_UP,      // Down then Up
    KEY_BACK,         // Back/exit
} ButtonType;

Rotation

typedef enum ROTATE {
    ROTATE_0,
    ROTATE_90,
    ROTATE_180,
    ROTATE_270,
} Rotate;

Bluetooth State

typedef enum BLUESTTE {
    DISCONNECTED,
    CONNECTING,
    CONNECTED,
} BlueState;

Weather Data

typedef enum WEATHERDAY {
    TOTDAY,         // Today
    TOMORROW,
    AFTERTOMOROW,   // Day after tomorrow
    DAY_COUNT,
} WeatherDay;

typedef struct TODAYDATA {
    uint16_t moonicon;      // Moon phase icon index
    uint16_t pressure;      // Air pressure
    uint16_t humidity;      // Humidity percentage
    uint8_t sunraise[6];    // Sunrise time string "HH:MM"
    uint8_t sunset[6];      // Sunset time string "HH:MM"
    uint8_t lunar[16];      // Lunar date string
} TodayData;

typedef struct WEATHER {
    uint8_t date;           // Day of month
    char day_temp;          // Daytime temperature
    char night_temp;        // Nighttime temperature
    uint16_t day_icon;      // Daytime weather icon
    uint16_t night_icon;    // Nighttime weather icon
} Weather;

Bitmap Format

MoWatch uses horizontal 8-point left-high-bit encoding:

// For a 120px wide image:
int16_t byteWidth = (120 + 7) / 8;  // = 15 bytes per row

// To check if pixel (x, y) is black:
if (bitmap[y * byteWidth + x / 8] & (128 >> (x & 7))) {
    // pixel is black
}

Project Structure

code

app_projects/
├── include/
│   └── header.h              # SDK header (from skill sdk/)
├── libs/
│   ├── init_datas.c          # SDK init (from skill sdk/)
│   ├── tiny-json.c           # JSON library (optional)
│   └── syscall_gcc.txt       # Syscall definitions (from skill sdk/)
└── app_yourapp/
    ├── code/
    │   ├── app_main.c        # Your main code
    │   └── graphics.h        # Your bitmap data (optional)
    └── gcc/
        ├── Makefile          # From skill templates/
        ├── app.ld            # From skill templates/
        └── createmwa.py      # From skill templates/

Complete API Reference

Drawing Functions

// Clear entire screen
void eink_clear(uint16_t color);

// Draw single pixel
void eink_drawpixel(uint16_t x, uint16_t y, uint16_t color);

// Draw line
void eink_drawline(uint16_t start_x, uint16_t start_y,
                   uint16_t end_x, uint16_t end_y, uint16_t color);

// Draw dashed line
void eink_drawdashedline(uint16_t start_x, uint16_t start_y,
                         uint16_t end_x, uint16_t end_y, uint16_t color);

// Draw rectangle (MODE_EMPTY=outline, MODE_FILL=filled)
void eink_drawrect(uint16_t start_x, uint16_t start_y,
                   uint16_t end_x, uint16_t end_y,
                   uint16_t color, uint8_t fill_mode);

// Draw circle
void eink_drawcircle(int x_center, int y_center, int radius,
                     int color, int fill_mode);

// Draw bitmap - THE MOST IMPORTANT FUNCTION!
// x, y: top-left position
// w, h: width and height in pixels
// data[]: bitmap array (horizontal 8-point left-high-bit)
// color: drawing color (BLACK or WHITE)
// transparent: 0=draw both colors, 1=only draw foreground
void eink_draw_bmp(uint16_t x, uint16_t y, uint16_t w, uint16_t h,
                   const uint8_t data[], uint16_t color, uint8_t transparent);

// Draw ASCII string
// Returns: width of drawn string
uint16_t eink_drawstr(uint16_t x, uint16_t y, const unsigned char *chr,
                      uint16_t size, uint16_t color);

// Draw Chinese string (UTF-8)
uint16_t eink_drawchstr(uint16_t x, uint16_t y, const unsigned char *chr,
                        uint16_t color);

// Draw string within rectangle bounds
uint16_t eink_draw_rectstr(const unsigned char *chr,
                           uint16_t start_x, uint16_t start_y,
                           uint16_t end_x, uint16_t end_y, uint16_t color);

// Set screen rotation
void eink_set_rotate(Rotate rotate);

// Get weather icon bitmap (32x32) into buffer
void get_weather_icon(uint16_t iconidx, uint8_t *buffer);

Time Functions

int RTC_getYear(void);      // Full year (e.g., 2024)
int RTC_getMon(void);       // Month 1-12
int RTC_getDay(void);       // Day 1-31
int RTC_getHour(void);      // Hour 0-23
int RTC_getMin(void);       // Minute 0-59
int RTC_getSec(void);       // Second 0-59
int RTC_getWeek(void);      // Day of week (0=Sunday)
int RTC_getTimeStamp(void); // Unix timestamp

System Functions

// Get battery percentage (0-100)
uint8_t watch_app_battpercent(void);

// Exit app, return to main menu
void watch_app_exit(void);

// Set update interval for onUpdate() callback (in milliseconds)
void set_update_interval(uint32_t interval);

// Get current update interval
uint32_t get_update_interval(void);

// Log message (for debugging)
void watch_app_log(char* log);

// Get Bluetooth connection state
BlueState watch_app_bluestate(void);

// Check if weather data is available
uint8_t watch_app_isweather_ok(void);

// Get today's data (sunrise, sunset, lunar, etc.)
TodayData watch_app_getToday(void);

// Get weather for specified day
Weather watch_app_getweather(WeatherDay day);

// HTTP request (async, result via callback)
void watch_app_http_req(const char* url, void(req_callback)(char*));

File Operations

// Read file
// Returns: bytes read
uint32_t watch_app_read_file(const uint8_t* file_name, uint8_t* buffer,
                             uint32_t len, uint32_t seekofs);

// Write file
// fa_mode: FA_CREATE_ALWAYS, FA_OPEN_APPEND, etc.
uint32_t watch_app_write_file(const uint8_t* file_name, uint8_t* buffer,
                              uint32_t len, uint32_t seekofs, uint8_t fa_mode);

// Delete file
uint8_t watch_app_delete_file(const uint8_t* file_name);

// Create directory
uint8_t watch_app_mkdir(const uint8_t* dir);

Memory Functions

// Allocate memory (use sparingly - only 4K RAM!)
void *m_malloc(uint32_t size);

// Free memory
void m_free(void *ptr);

Utility Functions

// Format string (like sprintf)
void co_sprintf(char *out, const char *format, ...);

// Get UTF-8 string length
uint16_t utf_len(const unsigned char *chr);

// Random number
int rand(void);
void srand(unsigned int seed);

Dialog Functions

// Show message dialog with OK/Cancel
// submit callback receives: 1=OK, 0=Cancel
void create_msg_dialog(const uint8_t* title, const uint8_t* msg,
                       void (*submit)(uint8_t ok));

// Show menu dialog
void create_menu_dialog(const char* title, const char** menu_item_names,
                        const uint8_t count, void (*submit)(uint8_t confirm));

// Show number picker dialog
void create_picker_dialog(uint8_t num, const uint8_t* nums,
                          const uint8_t count, void (*submit)(uint8_t data));

App Entry Points

#include "header.h"

// Called when screen needs to be drawn
void onDraw(void) {
    eink_clear(WHITE);
    // Draw your UI here
}

// Called when button is pressed
// Return update type to trigger screen refresh
UpdateType onKey(ButtonType key) {
    switch(key) {
        case KEY_BACK:
            watch_app_exit();
            break;
        case KEY_UP:
            // Handle up button
            break;
        case KEY_DOWN:
            // Handle down button
            break;
    }
    return PART_UPDATE;  // or NONE_UPDATE, FULL_UPDATE
}

// Called periodically based on set_update_interval()
UpdateType onUpdate(int delta) {
    static uint8_t lastmin = 61;
    if (lastmin != RTC_getMin()) {
        lastmin = RTC_getMin();
        return PART_UPDATE;  // Refresh screen when minute changes
    }
    return NONE_UPDATE;
}

// App initialization - REQUIRED
void app_init(intptr_t *draw_ptr_t, intptr_t *onkey_ptr_t,
              intptr_t *update_ptr_t, intptr_t* func_arr) {
    __initialize_datas(func_arr);
    *draw_ptr_t = (intptr_t)onDraw;
    *onkey_ptr_t = (intptr_t)onKey;
    *update_ptr_t = (intptr_t)onUpdate;

    // Initialize your variables here
    set_update_interval(1000);  // Check every 1 second
}

Complete Minimal Example

// app_main.c - Simple digital clock using eink_drawstr
#include "header.h"

void onDraw(void) {
    eink_clear(WHITE);

    char buf[32];

    // Draw time (large, centered)
    co_sprintf(buf, "%02d:%02d", RTC_getHour(), RTC_getMin());
    eink_drawstr(50, 80, (unsigned char*)buf, 32, BLACK);

    // Draw date
    co_sprintf(buf, "%04d-%02d-%02d", RTC_getYear(), RTC_getMon(), RTC_getDay());
    eink_drawstr(40, 130, (unsigned char*)buf, 16, BLACK);

    // Draw battery
    co_sprintf(buf, "BAT:%d%%", watch_app_battpercent());
    eink_drawstr(140, 5, (unsigned char*)buf, 12, BLACK);
}

UpdateType onKey(ButtonType key) {
    if (key == KEY_BACK || key == KEY_CENTER) {
        watch_app_exit();
    }
    return NONE_UPDATE;
}

UpdateType onUpdate(int delta) {
    static uint8_t lastmin = 61;
    if (lastmin != RTC_getMin()) {
        lastmin = RTC_getMin();
        if (RTC_getMin() % 5 == 0) {
            return FULL_UPDATE;
        }
        return PART_UPDATE;
    }
    return NONE_UPDATE;
}

void app_init(intptr_t *draw_ptr_t, intptr_t *onkey_ptr_t,
              intptr_t *update_ptr_t, intptr_t* func_arr) {
    __initialize_datas(func_arr);
    *draw_ptr_t = (intptr_t)onDraw;
    *onkey_ptr_t = (intptr_t)onKey;
    *update_ptr_t = (intptr_t)onUpdate;
    set_update_interval(1000);
}

Building with Docker

•Create Dockerfile (in SDK root, same level as app_projects):

dockerfile

FROM ubuntu:22.04
RUN apt-get update && apt-get install -y \
    gcc-arm-none-eabi \
    make \
    python3 \
    && rm -rf /var/lib/apt/lists/*
WORKDIR /build

•Build Docker image:

bash

docker build -t mowatch-sdk .

•Compile:

bash

docker run --rm -v "/path/to/app_projects:/build" mowatch-sdk make -C /build/app_yourapp/gcc

•Create .mwa package:

bash

cd gcc && python3 createmwa.py

Quick Start: Create New Project

•
Read SDK files from skill directory:
- •~/.claude/skills/mowatch-dev/sdk/include/header.h
- •~/.claude/skills/mowatch-dev/sdk/libs/init_datas.c
- •~/.claude/skills/mowatch-dev/sdk/libs/syscall_gcc.txt
•
Read template files:
- •~/.claude/skills/mowatch-dev/templates/Makefile
- •~/.claude/skills/mowatch-dev/templates/app.ld
- •~/.claude/skills/mowatch-dev/templates/createmwa.py
•
Create project structure and copy files:

bash

mkdir -p app_projects/include app_projects/libs
mkdir -p app_projects/app_mywatch/code app_projects/app_mywatch/gcc
# Copy SDK files to include/ and libs/
# Copy templates to gcc/
# Create app_main.c in code/

•
Edit createmwa.py to set outputmwa name
•
Build:

bash

docker run --rm -v "$(pwd)/app_projects:/build" mowatch-sdk make -C /build/app_mywatch/gcc
cd app_projects/app_mywatch/gcc && python3 createmwa.py

Image Processing for E-ink (Python)

Converting images to 1-bit bitmap:

python

from PIL import Image, ImageFilter

def process_for_eink(img_path, output_size=(120, 120)):
    img = Image.open(img_path).convert('RGB')
    img = img.resize(output_size, Image.Resampling.LANCZOS)
    gray = img.convert('L')
    edges = gray.filter(ImageFilter.FIND_EDGES)
    threshold = 128
    result = edges.point(lambda p: 0 if p > threshold else 255)
    return result

def image_to_c_array(img, var_name):
    """Convert PIL image to C header array"""
    width, height = img.size
    pixels = list(img.getdata())
    byte_width = (width + 7) // 8

    data = []
    for y in range(height):
        for bx in range(byte_width):
            byte = 0
            for bit in range(8):
                x = bx * 8 + bit
                if x < width:
                    idx = y * width + x
                    if pixels[idx] < 128:
                        byte |= (128 >> bit)
            data.append(byte)

    lines = [f"const unsigned char {var_name}[{len(data)}] = {{"]
    for i in range(0, len(data), 15):
        chunk = data[i:i+15]
        lines.append("    " + ", ".join(f"0x{b:02X}" for b in chunk) + ",")
    lines.append("};")
    return "\n".join(lines)

Installation to Watch

•Enable USB mode on MoWatch
•Mount appears as "NO NAME" volume
•Copy .mwa file to /apps/ folder
•Safely eject: diskutil eject "/Volumes/NO NAME"
•Select watch face from watch menu

Tips

•Memory: Only 4K RAM! Use const for all bitmap data
•Refresh: Use PART_UPDATE when possible, FULL_UPDATE every 5 minutes
•Graphics: Keep simple - e-ink has slow refresh
•Digits: 20x32px works well for time display
•Layout: Leave margins from screen edges for HUD-style designs
•Testing: Use watch_app_log() for debugging
•Battery: Check watch_app_battpercent() to show battery status