diagram.json

#include "gpio.h"
#include "spi.h"
#include "ili9341.h"
#include "uart.h"
//#include "HillelCLMMedium15.h"
//#include "NachlieliCLMLight15.h"
//#include "LiberationSansRegular15.h"
#include "gfx.h"
//#include "util/delay.h"
static uint8_t buf[30];
int main() {
	//gpio_pin_mode(PinD2, Output);
	//gpio_pin_set(PinD2);
	uart_enable_tx_only(115200);
	//_delay_ms(100);
	spi_enable();
	ili9341_enable();
	ili9341_set_pixel(0, 0, 0xFFFF);
	for (int x = 0; x < 27; x++)
		buf[x] = x;
	
//	font_t * font = &NachlieliCLMLight;
	//font_t * font = &HillelCLMMedium;
	//font_t * font = &LiberationSansRegular;
	gfx_draw_box(0, 0,128, 160, Silver);
	// /gfx_print(0, 0, "ABCDEFGHILMNOPQRSTUVWXZ0X22/3/2024X02:34:45", 24, false, font, Red);
	//gfx_print(239, 16, &buf, 27, true, font, Red);
	//gfx_draw_text_box(239, 32, 240, 16, &buf, 10, true, font, Green);
	//gfx_draw_text_box(239, 52, 240, 16, &buf, 16, true, font, Blue);
	while (1);
}


test-spi.c

#ifndef _spi_h_
#define _spi_h_

#include <stdint.h>
#include <stdbool.h>

#ifdef __cplusplus
extern "C" {
#endif
void spi_enable();
void spi_disable();
uint8_t spi_transfer8(uint8_t data);
void spi_transfer(uint8_t * data, uint8_t len);
#ifdef __cplusplus
}
#endif
#endif


spi.h

#include <avr/io.h>
#include "spi.h"

#define SPIDDR DDRB
#define SCK 5
#define MISO 4
#define MOSI 3

void spi_enable() {
	SPIDDR |= _BV(SCK) | _BV(MOSI);
	SPCR = _BV(SPE) | _BV(MSTR); // clock/4
}

void spi_disable() {
	SPCR = 0;
}

uint8_t spi_transfer8(uint8_t data) {
	SPDR = data;
	while (!(SPSR & _BV(SPIF)));
	return SPDR;
}

void spi_transfer(uint8_t * data, uint8_t len) {
	uint8_t *p = data;
	SPDR = *p;
	while (--len > 0) {
		uint8_t out = *(p + 1);
		while (!(SPSR & _BV(SPIF)));
		uint8_t in = SPDR;
		SPDR = out;
		*p++ = in;
	}
}


spi.c

#include <avr/io.h>
#include <avr/interrupt.h>
#include <string.h>
#include <stdbool.h>
#include "uart.h"

static uint8_t tx_buffer[UART_TX_BUFFER_SIZE + 1];
static volatile uint8_t tx_buffer_head;
static volatile uint8_t tx_buffer_tail;

static volatile uint8_t rx_buffer[UART_RX_BUFFER_SIZE + 1];
static volatile uint8_t rx_buffer_head;
static volatile uint8_t rx_buffer_tail;

void _uart_enable(uint32_t bitrate, bool enable_tx, bool enable_rx) {
	// SEL0=0 UPM0=0 USBS0=0 UCSZ0=3 async, no parity, 1 stop bit, 8 bit size
	UCSR0C |= _BV(UCSZ00) | _BV(UCSZ01);
	uint32_t b = (F_CPU / (bitrate * 16UL)) - 1;
	UBRR0L = b;
	UBRR0H = b >> 8;
	//if (enable_tx)
	//	UCSR0B |= _BV(TXEN0);
	if (enable_rx)
		UCSR0B |= _BV(RXEN0) | _BV(RXCIE0);
	sei();
}

void uart_enable(uint32_t bitrate) {
	_uart_enable(bitrate, true, true);
}

void uart_enable_tx_only(uint32_t bitrate) {
	_uart_enable(bitrate, true, false);
}

void uart_enable_rx_only(uint32_t bitrate) {
	_uart_enable(bitrate, false, true);
}

void uart_disable() {
	UCSR0B = 0;
	UCSR0C = 0;
}

bool uart_tx_buffer_is_empty() {
	return (tx_buffer_head == tx_buffer_tail);
}

void uart_write(uint8_t * data, uint8_t len) {
	bool empty = (tx_buffer_head == tx_buffer_tail);
	for (int i = 0; i < len; i++) {
		uint8_t next = (tx_buffer_head < UART_TX_BUFFER_SIZE ? tx_buffer_head + 1 : 0);
		tx_buffer[tx_buffer_head] = data[i];
		tx_buffer_head = next;
	}
	if (empty)
		UCSR0B |= _BV(TXEN0) | _BV(UDRIE0);
}

void uart_print(uint8_t * data) {
	uart_write(data, strlen((char *)data));
}

#if defined (__AVR_ATmega2560__)
#define USART_UDRE_vect USART0_UDRE_vect
#define USART_RX_vect USART0_RX_vect
#endif

ISR(USART_UDRE_vect) {
	if (tx_buffer_head != tx_buffer_tail) {
		uint8_t next = (tx_buffer_tail < UART_TX_BUFFER_SIZE ? tx_buffer_tail + 1 : 0);
		UDR0 = tx_buffer[tx_buffer_tail];
		tx_buffer_tail = next;
	} else
		UCSR0B &= ~_BV(TXEN0);
		//UCSR0B &= ~_BV(UDRIE0);
}

bool uart_data_is_available() {
	return (rx_buffer_head != rx_buffer_tail);
}

uint8_t uart_read() {
		if (rx_buffer_head == rx_buffer_tail)
			return 0;
		uint8_t next = (rx_buffer_tail < UART_RX_BUFFER_SIZE - 1 ? rx_buffer_tail + 1 : 0);
		uint8_t ch = rx_buffer[rx_buffer_tail];
		rx_buffer_tail = next;
		return ch;
}

ISR(USART_RX_vect) {
	uint8_t ch = UDR0;
	uint8_t next = (rx_buffer_head < UART_RX_BUFFER_SIZE - 1 ? rx_buffer_head + 1 : 0);
	if (next == rx_buffer_tail)
		return;
	rx_buffer[rx_buffer_head] = ch;
	rx_buffer_head = next;
}


uart.c

#ifndef _uart_h
#define _uart_h

#include <stdint.h>
#include <stdbool.h>

#if !defined(UART_TX_BUFFER_SIZE)
#define UART_TX_BUFFER_SIZE 250
#endif
#if !defined(UART_RX_BUFFER_SIZE)
#define UART_RX_BUFFER_SIZE 250
#endif

#ifdef __cplusplus
extern "C" {
#endif
void uart_enable(uint32_t bitrate);
void uart_enable_tx_only(uint32_t bitrate);
void uart_enable_rx_only(uint32_t bitrate);
void uart_disable();

bool uart_tx_buffer_is_empty();
void uart_write(uint8_t * data, uint8_t len);
void uart_print(uint8_t * str);

bool uart_data_is_available();
uint8_t uart_read();
#ifdef __cplusplus
}
#endif
#endif


uart.h

#include <avr/io.h>
#include <stdbool.h>
#include "gpio.h"

void gpio_pin_mode(gpio_pin_t pin, gpio_pin_mode_t mode) {
	volatile uint8_t * port = 0x20 + (2 + 3 * (pin >> 8));
	volatile uint8_t * ddr = 0x20 + (1 + 3 * (pin >> 8));
  uint8_t pin_mask = pin & 0xff;
	switch (mode) {
		case Input:
			*port &= ~pin_mask;
			break;
		case InputPullup:
      *ddr &= ~pin_mask;
      *port |= pin_mask;
			break;
		case Output:
			*ddr |= pin_mask;
			break;
	}
}

void gpio_pin_set(gpio_pin_t pin) {
	volatile uint8_t * port = 0x20 + (2 + 3 * (pin >> 8));
  uint8_t pin_mask = pin & 0xff;
  *port |= pin_mask;
}

void gpio_pin_clear(gpio_pin_t pin) {
	volatile uint8_t * port = 0x20 + (2 + 3 * (pin >> 8));
  uint8_t pin_mask = pin & 0xff;
  *port &= ~pin_mask;
}

void gpio_pin_write(gpio_pin_t pin, bool value) {
	if (value)
		gpio_pin_set(pin);
	else
		gpio_pin_clear(pin);
}


gpio.c

#ifndef _gpio_h
#define _gpio_h
#include <stdbool.h>

typedef enum {
  Input,
  InputPullup,
  Output,
} gpio_pin_mode_t;

typedef enum {
  PinA0 = 0x0001,
  PinA1 = 0x0002,
  PinA2 = 0x0004,
  PinA3 = 0x0008,
  PinA4 = 0x0010,
  PinA5 = 0x0020,
  PinA6 = 0x0040,
  PinA7 = 0x0080,
  PinB0 = 0x0101,
  PinB1 = 0x0102,
  PinB2 = 0x0104,
  PinB3 = 0x0108,
  PinB4 = 0x0110,
  PinB5 = 0x0120,
  PinB6 = 0x0140,
  PinB7 = 0x0180,
  PinC0 = 0x0201,
  PinC1 = 0x0202,
  PinC2 = 0x0204,
  PinC3 = 0x0208,
  PinC4 = 0x0210,
  PinC5 = 0x0220,
  PinC6 = 0x0240,
  PinC7 = 0x0280,
  PinD0 = 0x0301,
  PinD1 = 0x0302,
  PinD2 = 0x0304,
  PinD3 = 0x0308,
  PinD4 = 0x0310,
  PinD5 = 0x0320,
  PinD6 = 0x0340,
  PinD7 = 0x0380,
} gpio_pin_t;

#ifdef __cplusplus
extern "C" {
#endif
void gpio_pin_mode(gpio_pin_t pin, gpio_pin_mode_t mode);
void gpio_pin_set(gpio_pin_t pin);
void gpio_pin_clear(gpio_pin_t pin);
void gpio_pin_write(gpio_pin_t pin, bool value);
#ifdef __cplusplus
}
#endif
#endif


gpio.h

#include "ili9341.h"
#include <stdint.h>
#include <stdbool.h>
#include "gpio.h"
#include "spi.h"

#define BIT(x) (1<<x)

#ifdef __AVR__
#define CSPIN PinB2
#define DCPIN PinB1
#else
#define CSPIN PA4
#define DCPIN PA3
#endif

typedef enum {
	NOP = 0x00,
	SOFTWARE_RESET = 0x01,
	READ_INDENTIFICATION = 0x04,
	READ_DISPLAY_STATUS = 0x09,
	READ_DISPLAY_POWER_MODE = 0xa,
	READ_MEMORY_ACCESS_CONTROL = 0x0b,
	READ_DISPLAY_PIXEL_FORMAT = 0xc,
	READ_DISPLAY_IMAGE_FORMAT = 0xc,
	READ_SELF_DIAGNOSTIC = 0xF,
	//
	ENTER_SLEEP_MODE = 0x10,
	SLEEP_OUT = 0x11,
	PARTIAL_DISPLAY_MODE_ON = 0x12,
	NORMAL_DISPLAY_MODE_ON = 0x13,
	//
	DISPLAY_INVERSION_OFF = 0x20,
	DISPLAY_INVERSION_ON = 0x21,
	GAMMA_SET = 0x26,
	DISPLAY_OFF = 0x28,
	DISPLAY_ON = 0x29,
	COLUMN_ADDRESS_SET = 0x2a,
	PAGE_ADDRESS_SET = 0x2b,
	MEMORY_WRITE = 0x2c,
	COLOR_SET = 0x2d,
	MEMORY_READ = 0x2e,
	//
	PARTIAL_AREA = 0x30,
	VERTICAL_SCROLLING_DEFINITION = 0x33,
	TEARING_EFFECT_LINE_OFF = 0x34,
	TEARING_EFFECT_LINE_ON = 0x35 ,
	MEMORY_ACCESS_CONTROL = 0x36,
	VERTICAL_SCROLLING_START_ADDRESS = 0x37,
	IDLE_MODE_OFF = 0x38,
	IDLE_MODE_ON = 0x39,
	PIXEL_FORMAT_SET = 0x3A,
	WRITE_MEMORY_CONTINUE = 0x3C,
	READ_MEMORY_CONTINUE = 0x3D,
	//
	RGB_INTERFACE_SIGNAL_CONTROL = 0xB0,
	FRAME_RATE_CONTROL = 0xB1,
	FRAME_RATE_CONTROL2 = 0xB2,
	FRAME_RATE_CONTROL3 = 0xB3,
	DISPLAY_INVERSION_CONTROL = 0xB4,
	BLANKING_PORCH_CONTROL = 0xB5,
	DISPLAY_FUNCTION_CONTROL = 0xB6,
	ENTRY_MODE_SET = 0xB7,
	BACKLIGHT_CONTROL1 = 0xB8,
	BACKLIGHT_CONTROL2 = 0xB9,
	BACKLIGHT_CONTROL3 = 0xBA,
	BACKLIGHT_CONTROL4 = 0xBB,
	BACKLIGHT_CONTROL5 = 0xBC,
	BACKLIGHT_CONTROL6 = 0xBD,
	BACKLIGHT_CONTROL7 = 0xBE,
	BACKLIGHT_CONTROL8 = 0xBF,
	//
	POWER_CONTROL1 = 0xC0,
	POWER_CONTROL2 = 0xC1,
	VCOM_CONTROL1 = 0xC5,
	VCOM_CONTROL2 = 0xC7,
	//
	READ_ID1 = 0xDA,
	READ_ID2 = 0xDB,
	READ_ID3 = 0xDC,
	//
	POSITIVE_GAMMA_CORRECTION = 0xE0,
	NEGATIVE_GAMMA_CORRECTION = 0xE1,
	INTERFACE_CONTROL = 0xF6,
	// extended
	POWER_CONTROL_A = 0xCB,
	POWER_CONTROL_B = 0xCF,
	DRIVER_TIMING_CONTROL_A = 0xE8,
	DRIVER_TIMING_CONTROL_b = 0xEA,
	POWER_ON_SEQUENCE_CONTROL = 0xED,
	PUMP_RATIO_CONTROL = 0xF7
} ili9341_command_t;

// MEMORY_ACCESS_CONTROL 0x0b
#define MY 7 // row address order 0=top to bottom, 1=bottom to top
#define MX 6 // column addres order 0=left to right, 1=right to left
#define MV 5 // row/column exchange
#define ML 4 // vertical refresh order
#define BGR 3 // rgb/grb order
#define MH 2 // horizontal refresh order
// DISPLAY_FUNCTION_CONTROL 0xB6
#define PT0 0
#define PT1 1
#define PTG0 2
#define PTG1 3
//
#define ISC0 0
#define ISC1 1
#define ISC2 2
#define ISC3 3
#define ISC 0b00001111
#define SM 4
#define SS 5
#define GS 6
#define REV 7
//
#define NL 0b00111111

static void cslow() {
  gpio_pin_clear(CSPIN);
}

static void cshigh() {
  gpio_pin_set(CSPIN);
}

static void dclow() {
  gpio_pin_clear(DCPIN);
}

static void dchigh() {
  gpio_pin_set(DCPIN);
}

static void transmit_command(ili9341_command_t cmd) {
	dclow();
	cslow();
	spi_transfer8(cmd);
	cshigh();
	dchigh();
}

static void transmit_data(uint8_t data) {
	dchigh();
	cslow();
	spi_transfer8(data);
	cshigh();
}

static void transmit_data16(uint16_t data) {
	dchigh();
	cslow();
	spi_transfer8((uint8_t)(data >> 8));
	spi_transfer8(data );
	cshigh();
}

static void command(uint8_t cmd) {
	transmit_command(cmd);
}

static void command1(uint8_t cmd, uint8_t p1) {
	transmit_command(cmd);
	transmit_data(p1);
}

static void command2(uint8_t cmd, uint8_t p1, uint8_t p2) {
	transmit_command(cmd);
	transmit_data(p1);
	transmit_data(p2);
}

static void command3(uint8_t cmd, uint8_t p1, uint8_t p2, uint8_t p3) {
	transmit_command(cmd);
	transmit_data(p1);
	transmit_data(p2);
	transmit_data(p3);
}

static void command4(uint8_t cmd, uint8_t p1, uint8_t p2, uint8_t p3, uint8_t p4) {
	transmit_command(cmd);
	transmit_data(p1);
	transmit_data(p2);
	transmit_data(p3);
	transmit_data(p4);
}

void ili9341_enable() {
  gpio_pin_mode(CSPIN, Output);
  gpio_pin_mode(DCPIN, Output);
	command(SOFTWARE_RESET);
	//_delay_ms(50);
	command(DISPLAY_OFF);
	command1(POWER_CONTROL1, 0x23); // 4.60v
	command1(POWER_CONTROL2, 0x10); // ???
	command2(VCOM_CONTROL1, 0x2B, 0x2B); // 3.775V
	command1(VCOM_CONTROL2, 0xC0); // no offset voltage
	command1(MEMORY_ACCESS_CONTROL, BIT(MX) | BIT(BGR));
	command2(VERTICAL_SCROLLING_START_ADDRESS, 0, 0);
	command1(PIXEL_FORMAT_SET, 0x55); // 16bit/px
	command2(FRAME_RATE_CONTROL, 0, 0x1B);
	command3(DISPLAY_FUNCTION_CONTROL, BIT(PTG1), BIT(REV) + 2, 0x27);
	// TODO: set gamma
	command(SLEEP_OUT);
	//_delay_ms(150);
	command(DISPLAY_ON);
	//_delay_ms(200);
}

void ili9341_disable() {
	command(DISPLAY_OFF);
	command(ENTER_SLEEP_MODE);
}

void ili9341_set_pixel(uint16_t x, uint16_t y, uint16_t color) {
	uint8_t xh = x >> 8, xl = x & 0xff;
	uint8_t yh = y >> 8, yl = y & 0xff;
	uint8_t ch = (uint16_t)color >> 8, cl = (uint16_t)(color & 0xff);
	command4(COLUMN_ADDRESS_SET, xh, xl, xh + 1, xl + 1);
	command4(PAGE_ADDRESS_SET, yh, yl, yh + 1, yl + 1);
	command(MEMORY_WRITE);
	transmit_data(ch);
	transmit_data(cl);
}


ili9341.c

#ifndef _ili9341_h
#define _ili9341_h
#include <stdint.h>
#include <stdbool.h>

#ifdef __cplusplus
extern "C" {
#endif
void ili9341_enable();
void ili9341_disable();
void ili9341_set_pixel(uint16_t x, uint16_t y, uint16_t color);
#ifdef __cplusplus
}
#endif
#endif


ili9341.h

#include <stdint.h>
#include <stdbool.h>
#include "gfx.h"
#include "ili9341.h"

uint32_t font_data(font_t * font, uint8_t ch, uint8_t column) {
	uint8_t offset = 0;
	for (int i = 0; i < ch; i++)
		offset += font->size[i];
	return font->data[offset + column];
}

void gfx_set_pixel(uint16_t x, uint16_t y, rgb888_t color) {
	ili9341_set_pixel(x, y, RGB565(color));
}

void gfx_print(uint16_t x_, uint16_t y_, uint8_t * data, uint8_t len, bool rtl, font_t * font, rgb888_t color) {
	uint16_t xoff = 0;
	rgb888_t color0 = (rgb888_t){.red = 0, .green = 0, .blue = 0};
	rgb888_t color1 = (rgb888_t){.red = color.red * 0.8, .green = color.green * 0.8, .blue = color.blue * 0.8};
	rgb888_t color2 = (rgb888_t){.red = color.red * 0.5, .green = color.green * 0.5, .blue = color.blue * 0.5};
	rgb888_t colors[] = {color0, color2, color1, color};
	for (int i = 0; i < len; i++) {
		uint8_t size = font->size[i];
		for (uint8_t x = 0; x < size; x++) {
			uint8_t ch = *(data + i);
			uint32_t d = font_data(font, ch - font->offset, (rtl ? size - x - 1 : x));
			for (uint8_t y = 0; y < 16; y++) {
				uint8_t px = (d >> (2 * y)) &0x3;
				gfx_set_pixel((rtl ? x_ - xoff : x_ + xoff), y_ + y, colors[px]);
			}
			xoff += 1;
		} 
	}
}

void gfx_draw_text_box(uint16_t x_, uint16_t y_, uint16_t w, uint16_t h, uint8_t * data, uint8_t len, bool rtl, font_t * font, rgb888_t color) {
	uint16_t text_size = 0;
	for (int i = 0; i < len; i++)
		text_size += font->size[i];
	uint16_t pad = ((w - text_size) / 2); // center
	gfx_print((rtl ? w - pad : x_ + pad), y_, data, len, rtl, font, color);
}

void gfx_draw_box(uint16_t x_, uint16_t y_, uint16_t w, uint16_t h, rgb888_t color) {
	for (int y = y_; y < y_ + h; y++)
		for (int x = x_; x < x_ + w; x++)
			gfx_set_pixel(x, y, color);
}


gfx.c

#ifndef _gfx_h_
#define _gfx_h_
#include <stdint.h>
#include <stdbool.h>

typedef struct {
	uint8_t offset;
	uint8_t length;
	uint8_t * size;
	uint32_t *data;
} font_t;

typedef union {
	uint8_t value[3];
	struct {
		uint8_t red;
		uint8_t green;
		uint8_t blue;
	}
} rgb888_t;

#define RGB565(c) (((c.red >> 3) << 11) | ((c.green >> 2) << 5) | c.blue >> 3)

#define Red (rgb888_t){255, 0, 0}
#define Green (rgb888_t){0, 255, 0}
#define Blue (rgb888_t){0, 0, 255}
#define Gray (rgb888_t){32, 32, 32}
#define Silver (rgb888_t){192, 192, 192}

#ifdef __cplusplus
extern "C" {
#endif
uint32_t font_data(font_t * font, uint8_t ch, uint8_t column);
void gfx_print(uint16_t x, uint16_t y, uint8_t * data, uint8_t len, bool rtl, font_t * font, rgb888_t color);
void gfx_draw_text_box(uint16_t x, uint16_t y, uint16_t w, uint16_t h, uint8_t * data, uint8_t len, bool rtl, font_t * font, rgb888_t color);
void gfx_draw_box(uint16_t x, uint16_t y, uint16_t w, uint16_t h, rgb888_t color);
#ifdef __cplusplus
}
#endif
#endif


gfx.h

#include "st7735.h"
#include <stdint.h>
#include <stdbool.h>
#include "gpio.h"
#include "spi.h"

#define BIT(x) (1<<x)

#ifdef __AVR__
#define CSPIN PinB2
#define DCPIN PinB1
#else
#define CSPIN PA4
#define DCPIN PA3
#endif

typedef enum {
	NOP = 0x00,
	SOFTWARE_RESET = 0x01,
	READ_DISPLAY_ID = 0x04,
	READ_DISPLAY_STATUS = 0x09,
	READ_DISPLAY_POWER_MODE = 0xA,
	READ_MEMORY_ACCESS_CONTROL = 0x0B,
	READ_DISPLAY_PIXEL_FORMAT = 0xC,
	READ_DISPLAY_IMAGE_FORMAT = 0xD,
	READ_DISPLAY_SIGNAL_MODE = 0x0E,
	READ_SELF_DIAGNOSTIC = 0xF,
	//
	SLEEP_IN = 0x10,
	SLEEP_OUT = 0x11,
	PARTIAL_DISPLAY_MODE_ON = 0x12,
	NORMAL_DISPLAY_MODE_ON = 0x13,
	//
	DISPLAY_INVERSION_OFF = 0x20,
	DISPLAY_INVERSION_ON = 0x21,
	GAMMA_SET = 0x26,
	DISPLAY_OFF = 0x28,
	DISPLAY_ON = 0x29,
	COLUMN_ADDRESS_SET = 0x2a,
	ROW_ADDRESS_SET = 0x2b,
	MEMORY_WRITE = 0x2c,
	COLOR_SETTING = 0x2d,
	MEMORY_READ = 0x2e,
	//
	PARTIAL_AREA = 0x30,
	SCROLL_AREA_SET = 0x33,
	TEARING_EFFECT_LINE_OFF = 0x34,
	TEARING_EFFECT_LINE_ON = 0x35 ,
	MEMORY_ACCESS_CONTROL = 0x36,
	VERTICAL_SCROLL_START_ADDRESS = 0x37,
	IDLE_MODE_OFF = 0x38,
	IDLE_MODE_ON = 0x39,
	INTERFACE_PIXEL_FORMAT = 0x3A,
	//
	FRAME_RATE_CONTROL = 0xB1,
	FRAME_RATE_CONTROL2 = 0xB2,
	FRAME_RATE_CONTROL3 = 0xB3,
	DISPLAY_INVERSION_CONTROL = 0xB4,
	//
	POWER_CONTROL1 = 0xC0,
	POWER_CONTROL2 = 0xC1,
	POWER_CONTROL3 = 0xC2,
	POWER_CONTROL4 = 0xC3,
	POWER_CONTROL5 = 0xC4,
	VCOM_CONTROL1 = 0xC5,
	VCOM_OFFSET_CONTROL = 0xC7,
	//
	WRITE_ID2_VALUE = 0xD1,
	WRITE_ID3_VALUE = 0xD2,
	NVM_CONTROL_STATUS = 0xD9,
	READ_ID1_VALUE = 0xDA,
	READ_ID2_VALUE = 0xDB,
	READ_ID3_VALUE = 0xDC,
	NVM_READ_COMMAND = 0xDE,
	NVM_WRITE_COMMAND = 0xDF,
	//
	POSITIVE_GAMMA_CORRECTION = 0xE0,
	NEGATIVE_GAMMA_CORRECTION = 0xE1,
	//
	GATE_PUMP_CLOCK_FREQUENCY = 0xFC,
} st7735_command_t;

// MEMORY_ACCESS_CONTROL 0x0b
#define MY 7 // row address order 0=top to bottom, 1=bottom to top
#define MX 6 // column addres order 0=left to right, 1=right to left
#define MV 5 // row/column exchange
#define ML 4 // vertical refresh order
#define BGR 3 // rgb/grb order
#define MH 2 // horizontal refresh order
// DISPLAY_INVERSION_CONTROL 0xB4
#define NLC 0
#define NLB 1
#define NLA 2

static void cslow() {
  gpio_pin_clear(CSPIN);
}

static void cshigh() {
  gpio_pin_set(CSPIN);
}

static void dclow() {
  gpio_pin_clear(DCPIN);
}

static void dchigh() {
  gpio_pin_set(DCPIN);
}

static void transmit_command(st7735_command_t cmd) {
	dclow();
	cslow();
	spi_transfer8(cmd);
	cshigh();
	dchigh();
}

static void transmit_data(uint8_t data) {
	dchigh();
	cslow();
	spi_transfer8(data);
	cshigh();
}

static void transmit_data16(uint16_t data) {
	dchigh();
	cslow();
	spi_transfer8((uint8_t)(data >> 8));
	spi_transfer8(data );
	cshigh();
}

static void command(uint8_t cmd) {
	transmit_command(cmd);
}

static void command1(uint8_t cmd, uint8_t p1) {
	transmit_command(cmd);
	transmit_data(p1);
}

static void command2(uint8_t cmd, uint8_t p1, uint8_t p2) {
	transmit_command(cmd);
	transmit_data(p1);
	transmit_data(p2);
}

static void command3(uint8_t cmd, uint8_t p1, uint8_t p2, uint8_t p3) {
	transmit_command(cmd);
	transmit_data(p1);
	transmit_data(p2);
	transmit_data(p3);
}

static void command4(uint8_t cmd, uint8_t p1, uint8_t p2, uint8_t p3, uint8_t p4) {
	transmit_command(cmd);
	transmit_data(p1);
	transmit_data(p2);
	transmit_data(p3);
	transmit_data(p4);
}

void st7735_enable() {
  gpio_pin_mode(CSPIN, Output);
  gpio_pin_mode(DCPIN, Output);
	command(SOFTWARE_RESET);
	//_delay_ms(50);
	command(SLEEP_OUT);
	//_delay_ms(500);
	command1(INTERFACE_PIXEL_FORMAT, 0x05); // 16bit/px
	//_delay_ms(10);
	command3(FRAME_RATE_CONTROL,
			0, // fastest refresh
			6, // 6 lines front porch
			3); // 3 lines back porch
	//_delay_ms(10);
	command1(MEMORY_ACCESS_CONTROL, BIT(MX) | BIT(BGR));
	// DISPLAY_SETTING5 0x15, 0x02
	// DISPLAY_INVERSION_CONTROL, 0
	command2(POWER_CONTROL1,
		0x23, // 4.70v
		0x70); // 1.0uA
	//_delay_ms(10);
	command1(POWER_CONTROL2, 0x05); // vgh=14.7v, vgl=-14.35
	command2(POWER_CONTROL3,
		0x01, // opamp curent small
		0x02); // boost frequency

	command(DISPLAY_OFF);
	command2(VCOM_CONTROL1, 0x2B, 0x2B); // 3.775V
	command1(VCOM_OFFSET_CONTROL, 0xC0); // no offset voltage ?
	command2(VERTICAL_SCROLL_START_ADDRESS, 0, 0);
	//command3(DISPLAY_FUNCTION_CONTROL, BIT(PTG1), BIT(REV) + 2, 0x27);
	// TODO: set gamma
	command(DISPLAY_ON);
	//_delay_ms(200);
}

void st7735_disable() {
	command(DISPLAY_OFF);
	command(SLEEP_IN);
}

void st7735_set_pixel(uint16_t x, uint16_t y, uint16_t color) {
	uint8_t xh = x >> 8, xl = x & 0xff;
	uint8_t yh = y >> 8, yl = y & 0xff;
	uint8_t ch = (uint16_t)color >> 8, cl = (uint16_t)(color & 0xff);
	command4(COLUMN_ADDRESS_SET, xh, xl, xh + 1, xl + 1);
	command4(ROW_ADDRESS_SET, yh, yl, yh + 1, yl + 1);
	command(MEMORY_WRITE);
	transmit_data(ch);
	transmit_data(cl);
}


st7735.c

#ifndef _st7735_h
#define _st7735_h
#include <stdint.h>
#include <stdbool.h>

#ifdef __cplusplus
extern "C" {
#endif
void st7735_enable();
void st7735_disable();
void st7735_set_pixel(uint16_t x, uint16_t y, uint16_t color);
#ifdef __cplusplus
}
#endif
#endif
