micropython-st7789-lcd-driver/README.md

ST7789 Driver for MicroPython
=============================


Overview
--------
This is a driver for MicroPython to handle cheap displays
based on ST7789 chip.

<p align="center">
  <img src="https://raw.githubusercontent.com/devbis/st7789_mpy/master/docs/ST7789.jpg" alt="ST7789 display photo"/>
</p>

It supports both 240x240 and 135x240 variants of displays.

It is written in pure C, so you have to build
firmware by yourself.
ESP8266, ESP32, and STM32 ports are supported for now.


Building instruction
---------------------

Prepare build tools as described in the manual.
You should follow the instruction for building MicroPython and
ensure that you can build the firmware without this display module.

Clone this module alongside the MPY sources:

    git clone https://github.com/devbis/st7789_mpy.git

Go to MicroPython ports directory and for ESP8266 run:

    cd micropython/ports/esp8266

for ESP32:

    cd micropython/ports/esp32

And then compile the module with specified USER_C_MODULES dir

    make USER_C_MODULES=../../../st7789_mpy/ all


If you have other user modules, copy the st7789_driver/st7789 to
the user modules directory

Upload the resulting firmware to your MCU as usual with esptool.py
(See
[MicroPython docs](http://docs.micropython.org/en/latest/esp8266/tutorial/intro.html#deploying-the-firmware)
for more info)

    make deploy

Working examples
----------------

This module was tested on ESP32 and ESP8266 MCUs.

You have to provide `machine.SPI` object and at least two pins for RESET and
DC pins on the screen for the display object.


    # ESP 8266

    import machine
    import st7789
    spi = machine.SPI(1, baudrate=40000000, polarity=1)
    display = st7789.ST7789(spi, 240, 240, reset=machine.Pin(5, machine.Pin.OUT), dc=machine.Pin(4, machine.Pin.OUT))
    display.init()


For ESP32 modules you have to provide specific pins for SPI.
Unfortunately, I was unable to run this display on SPI(1) interface.
For machine.SPI(2) == VSPI you have to use

- CLK: Pin(18)
- MOSI: Pin(23)

Other SPI pins are not used.


    # ESP32

    import machine
    import st7789
    spi = machine.SPI(2, baudrate=40000000, polarity=1, sck=machine.Pin(18), mosi=machine.Pin(23))
    display = st7789.ST7789(spi, 240, 240, reset=machine.Pin(4, machine.Pin.OUT), dc=machine.Pin(2, machine.Pin.OUT))
    display.init()


I couldn't run the display on an SPI with baudrate higher than 40MHZ

Also, the driver was tested on STM32 board:


    # STM32
    
    import machine
    import st7789
    spi = machine.SPI(2, baudrate=12000000, polarity=1)
    display = st7789.ST7789(spi, 135, 240, reset=machine.Pin('B3', machine.Pin.OUT), dc=machine.Pin('B6', machine.Pin.OUT))
    display.init()


Methods
-------------

This driver supports only 16bit colors in RGB565 notation.


- `ST7789.fill(color)`

  Fill the entire display with the specified color.

- `ST7789.pixel(x, y, color)`

  Set the specified pixel to the given color.

- `ST7789.line(x0, y0, x1, y1, color)`

  Draws a single line with the provided `color` from (`x0`, `y0`) to
  (`x1`, `y1`).

- `ST7789.hline(x, y, length, color)`

  Draws a single horizontal line with the provided `color` and `length`
  in pixels. Along with `vline`, this is a fast version with reduced
  number of SPI calls.

- `ST7789.vline(x, y, length, color)`

  Draws a single horizontal line with the provided `color` and `length`
  in pixels.

- `ST7789.rect(x, y, width, height, color)`

  Draws a rectangle from (`x`, `y`) with corresponding dimensions

- `ST7789.fill_rect(x, y, width, height, color)`

  Fill a rectangle starting from (`x`, `y`) coordinates

- `ST7789.blit_buffer(buffer, x, y, width, height)`

  Copy bytes() or bytearray() content to the screen internal memory.
  Note: every color requires 2 bytes in the array

Also, the module exposes predefined colors:
  `BLACK`, `BLUE`, `RED`, `GREEN`, `CYAN`, `MAGENTA`, `YELLOW`, and `WHITE`


Helper functions
----------------

- `color565(r, g, b)`

  Pack a color into 2-bytes rgb565 format

- `map_bitarray_to_rgb565(bitarray, buffer, width, color=WHITE, bg_color=BLACK)`

  Convert a bitarray to the rgb565 color buffer which is suitable for blitting.
  Bit 1 in bitarray is a pixel with `color` and 0 - with `bg_color`.

  This is a helper with a good performance to print text with a high
  resolution font. You can use an awesome tool
  https://github.com/peterhinch/micropython-font-to-py
  to generate a bitmap fonts from .ttf and use them as a frozen bytecode from
  the ROM memory.

Performance
-----------

For the comparison I used an excellent library for Arduino
that can handle this screen.

https://github.com/ananevilya/Arduino-ST7789-Library/

Also, I used my slow driver for this screen, written in pure python.

https://github.com/devbis/st7789py_mpy/

I used these modules to draw a line from 0,0 to 239,239
The table represents the time in milliseconds for each case

|         | Arduino-ST7789 | st7789py_mpy | st7789_mpy    |
|---------|----------------|--------------|---------------|
| ESP8266 | 26             | 450          | 12            |
| ESP32   | 23             | 450          | 47            |


As you can see, the ESP32 module draws a line 4 times slower than
the older ESP8266 module.


Troubleshooting
---------------

#### Overflow of iram1_0_seg

When building a firmware for esp8266 you can see this failure message from
the linker:

    LINK build/firmware.elf
    xtensa-lx106-elf-ld: build/firmware.elf section `.text' will not fit in region `iram1_0_seg'
    xtensa-lx106-elf-ld: region `iram1_0_seg' overflowed by 292 bytes
    Makefile:192: recipe for target 'build/firmware.elf' failed

To fix this issue, you have to put st7789 module to irom0 section.
Edit `esp8266_common.ld` file in the `ports/esp8266` dir and add a line

    *st7789/*.o(.literal* .text*)

in the `.irom0.text : ALIGN(4)` section


#### Unsupported dimensions

This driver supports only 240x240 and 135x240 pixel displays.
If you have a display with an unsupported resolution, you can pass
`xstart` and `ystart` parameters to the display constructor to set the
required offsets.