PineTime ST7789 LCD Driver for Apache Mynewt

This is a minimal, efficient driver for the ST7789 display on the PineTime smartwatch, designed specifically for the Apache Mynewt embedded OS.

Features

• No heap usage
• Non-blocking (DMA) SPI interface
• Flash-friendly with interleaved decompression support
• Partial updates (great for UI icons or widgets)
• Basic drawing primitives
• Small memory footprint

Who is this for?

Embedded developers working with:

• The PineTime smartwatch
• Apache Mynewt RTOS
• Custom firmware or bootloaders
• or other constrained devices

Example Usage

Below is a simplified example showing how to initialize the display and stream a full-screen image using double buffering. This assumes your image is stored in flash in RGB565, little endian format.

#include "pinetime_st7789/pinetime_st7789.h"

static uint8_t *next(uint8_t *buf, int *chunk, int remaining_len)
{
  static uint8_t internal_buf[2][PINETIME_ST7789_MAXTRANSFER];
  static uint8_t *external_buf;
  static int buf_idx = 0;
  int len;
  uint8_t *ret = NULL;

  if (chunk)
  {
    len = min(PINETIME_ST7789_MAXTRANSFER, remaining_len);
    memcpy(internal_buf[buf_idx], external_buf, len);  // Flash -> RAM for DMA access
    *chunk = len;
    external_buf += len;
    ret = internal_buf[buf_idx];
    buf_idx ^= 1;
  }
  else
  {
    external_buf = buf;
    buf_idx = 0;
  }

  return ret;
}

static void maintask(void *arg)
{
  pinetime_st7789_init(PINETIME_PXLFMT_RGB565);
  pinetime_st7789_clear();
  pinetime_st7789_brightness(PINETIME_BRIGHTNESS_HIGH);

  int len = PINETIME_ST7789_SCR_WIDTH * PINETIME_ST7789_SCR_HEIGHT * 2;
  next((uint8_t *)image_array, NULL, len);
  pinetime_st7789_stream_frame(next, len);
}

Building with Newt

You can build and load the driver using the Apache Mynewt newt tool. Here's a basic setup flow:

newt new lcdtest
cd lcdtest
newt upgrade

Create bootloader target:

newt target create boot-pinetime
newt target set boot-pinetime app=@mcuboot/boot/mynewt
newt target set boot-pinetime bsp=@apache-mynewt-core/hw/bsp/pinetime
newt target set boot-pinetime build_profile=optimized

Create app target:

newt target create lcdtest-pinetime
newt target set lcdtest-pinetime app=apps/lcdtest
newt target set lcdtest-pinetime bsp=@apache-mynewt-core/hw/bsp/pinetime
newt target set lcdtest-pinetime build_profile=debug

Clone this driver:

cd repos
git clone https://github.com/gega/mynewt-pinetime-st7789.git
cd ..

Update apps/lcdtest/pkg.yml and add these dependencies:

pkg.deps:
    - "@mynewt-pinetime-st7789/hw/drivers/display/pinetime_st7789"
    - "@apache-mynewt-core/hw/drivers/flash/spiflash"

Then build and flash:

newt build boot-pinetime
newt build lcdtest-pinetime
newt create-image boot-pinetime 1.0.0
newt create-image lcdtest-pinetime 1.0.0
newt load boot-pinetime
newt load lcdtest-pinetime

Repository Structure

mynewt-pinetime-st7789/
└── hw/
    └── drivers/
        └── display/
            └── pinetime_st7789/

Demo

https://github.com/user-attachments/assets/e198a00d-b2b0-4b1a-beb6-43dda7f9212d

using the ninety3d and the sbuf libraries