Adding an ST7789 display to my Microbit V2 and Zephyr setup

I wanted to learn about using an external SPI device with the BBC Microbit V2. I ported my ST7789 library over to a Zephyr based program shown running on the Microbit and it is shown in operation above. The SPI interface runs at a fairly slow 8MHz which I believe (for now) is the maximum for this interface. As a result, screen updates are not super quick but probably good enough for a simple user interface.

The display library supports the following functions:

int display_begin();
void display_command(uint8_t cmd);
void display_data(uint8_t data);
void display_openAperture(uint16_t x1, uint16_t y1, uint16_t x2, uint16_t y2);
void display_putPixel(uint16_t x, uint16_t y, uint16_t colour);
void display_putImage(uint16_t x, uint16_t y, uint16_t width, uint16_t height, uint16_t *Image);
void display_drawLine(uint16_t x0, uint16_t y0, uint16_t x1, uint16_t y1, uint16_t Colour);
int iabs(int x); // simple integer version of abs for use by graphics functions
void display_drawRectangle(uint16_t x, uint16_t y, uint16_t w, uint16_t h, uint16_t Colour);
void display_fillRectangle(uint16_t x,uint16_t y,uint16_t width, uint16_t height, uint16_t colour);
void display_drawCircle(uint16_t x0, uint16_t y0, uint16_t radius, uint16_t Colour);
void display_fillCircle(uint16_t x0, uint16_t y0, uint16_t radius, uint16_t Colour);
void display_print(const char *Text, uint16_t len, uint16_t x, uint16_t y, uint16_t ForeColour, uint16_t BackColour);
uint16_t display_RGBToWord(uint16_t R, uint16_t G, uint16_t B);

Code is available over here on github.

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