fix pcb, connect button to VCC instead of GND

oled_gol.c

@@ -1,23 +1,133 @@
-/* Template app on which you can build your own. */
 
+#define SSD1306_128X32
 #include "ch32v003fun.h"
 #include <stdio.h>
+#include "ssd1306_i2c.h"
+#include "ssd1306.h"
 
 #define PIN_LED PC4
+#define PIN_BTN PC7
+
+#define u8 uint8_t
+#define u16 uint16_t
+
+uint8_t gol_tmp[sizeof(ssd1306_buffer)];
+
+uint32_t lfsr = 1; // PRNG state
+
+u8 rand8();
+u8 get_pixel(u8 x, u8 y);
+void gol_step();
+void r_pentomino();
+void randomise();
 
 int main()
 {
 	SystemInit();
-
 	funGpioInitAll();
+	funPinMode(PIN_LED, GPIO_CFGLR_OUT_10Mhz_PP);
+	funPinMode(PIN_BTN, GPIO_CFGLR_IN_PUPD);
 
-	funPinMode(PIN_LED, GPIO_Speed_10MHz | GPIO_CNF_OUT_PP);
+	ssd1306_i2c_init();
+	ssd1306_init();
+	randomise();
 
 	while (1)
 	{
-		funDigitalWrite(PIN_LED, FUN_HIGH);
-		Delay_Ms(150);
-		funDigitalWrite(PIN_LED, FUN_LOW);
-		Delay_Ms(150);
+		ssd1306_refresh();
+		gol_step();
+		memcpy(ssd1306_buffer, gol_tmp, sizeof(ssd1306_buffer));
+
+		if (funDigitalRead(PIN_BTN))
+		{
+			randomise();
+			ssd1306_refresh();
+			funDigitalWrite(PIN_LED, FUN_HIGH);
+			Delay_Ms(100);
+			funDigitalWrite(PIN_LED, FUN_LOW);
+		}
 	}
 }
+
+void r_pentomino()
+{
+	ssd1306_setbuf(0);
+	ssd1306_drawPixel(20, 20, 1);
+	ssd1306_drawPixel(21, 20, 1);
+	ssd1306_drawPixel(21, 21, 1);
+	ssd1306_drawPixel(22, 21, 1);
+	ssd1306_drawPixel(21, 22, 1);
+}
+
+void randomise()
+{
+	lfsr = SysTick->CNT;
+	for (u16 b = 0; b < sizeof(ssd1306_buffer); b++)
+	{
+		ssd1306_buffer[b] = rand8();
+	}
+}
+
+u8 get_pixel(u8 x, u8 y)
+{
+	x = x & 127;
+	y = y & 31;
+	u8 slice = ssd1306_buffer[(y / 8) * 128 + x];
+	return (slice & (1 << (y & 7))) != 0;
+}
+
+void gol_step()
+{
+	// slow pixel-by-pixel implementation
+	for (u8 x = 0; x < 128; x++)
+	{
+		for (u8 y = 0; y < 32; y++)
+		{
+			u8 this = get_pixel(x, y);
+			u8 sum = 0;
+			sum += get_pixel(x + 127, y + 31);
+			sum += get_pixel(x + 127, y);
+			sum += get_pixel(x + 127, y + 1);
+			sum += get_pixel(x, y + 31);
+			sum += get_pixel(x, y + 1);
+			sum += get_pixel(x + 1, y + 31);
+			sum += get_pixel(x + 1, y);
+			sum += get_pixel(x + 1, y + 1);
+
+			u8 new_state = (sum == 3) | ((sum == 2) & this);
+			u16 addr = x + (y / 8) * 128;
+
+			if (new_state)
+				gol_tmp[addr] |= (1 << (y & 7));
+			else
+				gol_tmp[addr] &= ~(1 << (y & 7));
+		}
+	}
+}
+
+/* White Noise Generator State */
+#define NOISE_BITS 8
+#define NOISE_MASK ((1 << NOISE_BITS) - 1)
+#define NOISE_POLY_TAP0 31
+#define NOISE_POLY_TAP1 21
+#define NOISE_POLY_TAP2 1
+#define NOISE_POLY_TAP3 0
+/*
+ * random byte generator, taken from ch32v003fun examples
+ */
+uint8_t rand8(void)
+{
+	uint8_t bit;
+	uint32_t new_data;
+
+	for (bit = 0; bit < NOISE_BITS; bit++)
+	{
+		new_data = ((lfsr >> NOISE_POLY_TAP0) ^
+					(lfsr >> NOISE_POLY_TAP1) ^
+					(lfsr >> NOISE_POLY_TAP2) ^
+					(lfsr >> NOISE_POLY_TAP3));
+		lfsr = (lfsr << 1) | (new_data & 1);
+	}
+
+	return lfsr & NOISE_MASK;
+}

ssd1306.h

@@ -0,0 +1,489 @@
+/*
+ * Single-File-Header for using SPI OLED
+ * 05-05-2023 E. Brombaugh
+ */
+
+#ifndef _SSD1306_H
+#define _SSD1306_H
+
+#include <stdint.h>
+#include <string.h>
+
+// comfortable packet size for this OLED
+#define SSD1306_PSZ 32
+
+// characteristics of each type
+#if !defined(SSD1306_64X32) && !defined(SSD1306_128X32) && !defined(SSD1306_128X64)
+#error "Please define the SSD1306_WXH resolution used in your application"
+#endif
+
+#ifdef SSD1306_64X32
+#define SSD1306_W 64
+#define SSD1306_H 32
+#define SSD1306_FULLUSE
+#define SSD1306_OFFSET 32
+#endif
+
+#ifdef SSD1306_128X32
+#define SSD1306_W 128
+#define SSD1306_H 32
+#define SSD1306_OFFSET 0
+#endif
+
+#ifdef SSD1306_128X64
+#define SSD1306_W 128
+#define SSD1306_H 64
+#define SSD1306_FULLUSE
+#define SSD1306_OFFSET 0
+#endif
+
+/*
+ * send OLED command byte
+ */
+uint8_t ssd1306_cmd(uint8_t cmd)
+{
+	ssd1306_pkt_send(&cmd, 1, 1);
+	return 0;
+}
+
+/*
+ * send OLED data packet (up to 32 bytes)
+ */
+uint8_t ssd1306_data(uint8_t *data, uint8_t sz)
+{
+	ssd1306_pkt_send(data, sz, 0);
+	return 0;
+}
+
+#define SSD1306_SETCONTRAST 0x81
+#define SSD1306_SEGREMAP 0xA0
+#define SSD1306_DISPLAYALLON_RESUME 0xA4
+#define SSD1306_DISPLAYALLON 0xA5
+#define SSD1306_NORMALDISPLAY 0xA6
+#define SSD1306_INVERTDISPLAY 0xA7
+#define SSD1306_DISPLAYOFF 0xAE
+#define SSD1306_DISPLAYON 0xAF
+#define SSD1306_SETDISPLAYOFFSET 0xD3
+#define SSD1306_SETCOMPINS 0xDA
+#define SSD1306_SETVCOMDETECT 0xDB
+#define SSD1306_SETDISPLAYCLOCKDIV 0xD5
+#define SSD1306_SETPRECHARGE 0xD9
+#define SSD1306_SETMULTIPLEX 0xA8
+#define SSD1306_SETLOWCOLUMN 0x00
+#define SSD1306_SETHIGHCOLUMN 0x10
+#define SSD1306_SETSTARTLINE 0x40
+#define SSD1306_MEMORYMODE 0x20
+#define SSD1306_COLUMNADDR 0x21
+#define SSD1306_PAGEADDR 0x22
+#define SSD1306_COMSCANINC 0xC0
+#define SSD1306_COMSCANDEC 0xC8
+#define SSD1306_CHARGEPUMP 0x8D
+#define SSD1306_EXTERNALVCC 0x1
+#define SSD1306_SWITCHCAPVCC 0x2
+#define SSD1306_TERMINATE_CMDS 0xFF
+
+/* choose VCC mode */
+#define SSD1306_EXTERNALVCC 0x1
+#define SSD1306_SWITCHCAPVCC 0x2
+// #define vccstate SSD1306_EXTERNALVCC
+#define vccstate SSD1306_SWITCHCAPVCC
+
+// OLED initialization commands for 128x32
+const uint8_t ssd1306_init_array[] =
+	{
+		SSD1306_DISPLAYOFF,			// 0xAE
+		SSD1306_SETDISPLAYCLOCKDIV, // 0xD5
+		0x80,						// the suggested ratio 0x80
+		SSD1306_SETMULTIPLEX,		// 0xA8
+#ifdef SSD1306_64X32
+		0x1F, // for 64-wide displays
+#else
+		0x3F, // for 128-wide displays
+#endif
+		SSD1306_SETDISPLAYOFFSET,	// 0xD3
+		0x00,						// no offset
+		SSD1306_SETSTARTLINE | 0x0, // 0x40 | line
+		SSD1306_CHARGEPUMP,			// 0x8D
+		0x14,						// enable?
+		SSD1306_MEMORYMODE,			// 0x20
+		0x00,						// 0x0 act like ks0108
+		SSD1306_SEGREMAP | 0x1,		// 0xA0 | bit
+		SSD1306_COMSCANDEC,
+		SSD1306_SETCOMPINS,	 // 0xDA
+		0x12,				 //
+		SSD1306_SETCONTRAST, // 0x81
+		0x8F,
+		SSD1306_SETPRECHARGE, // 0xd9
+		0xF1,
+		SSD1306_SETVCOMDETECT, // 0xDB
+		0x40,
+		SSD1306_DISPLAYALLON_RESUME, // 0xA4
+		SSD1306_NORMALDISPLAY,		 // 0xA6
+		SSD1306_DISPLAYON,			 // 0xAF --turn on oled panel
+		SSD1306_TERMINATE_CMDS		 // 0xFF --fake command to mark end
+};
+
+// the display buffer
+uint8_t ssd1306_buffer[SSD1306_W * SSD1306_H / 8];
+
+/*
+ * set the buffer to a color
+ */
+void ssd1306_setbuf(uint8_t color)
+{
+	memset(ssd1306_buffer, color ? 0xFF : 0x00, sizeof(ssd1306_buffer));
+}
+
+#ifndef SSD1306_FULLUSE
+/*
+ * expansion array for OLED with every other row unused
+ */
+const uint8_t expand[16] =
+	{
+		0x00,
+		0x02,
+		0x08,
+		0x0a,
+		0x20,
+		0x22,
+		0x28,
+		0x2a,
+		0x80,
+		0x82,
+		0x88,
+		0x8a,
+		0xa0,
+		0xa2,
+		0xa8,
+		0xaa,
+};
+#endif
+
+/*
+ * Send the frame buffer
+ */
+void ssd1306_refresh(void)
+{
+	uint16_t i;
+
+	ssd1306_cmd(SSD1306_COLUMNADDR);
+	ssd1306_cmd(SSD1306_OFFSET);				 // Column start address (0 = reset)
+	ssd1306_cmd(SSD1306_OFFSET + SSD1306_W - 1); // Column end address (127 = reset)
+
+	ssd1306_cmd(SSD1306_PAGEADDR);
+	ssd1306_cmd(0); // Page start address (0 = reset)
+	ssd1306_cmd(7); // Page end address
+
+#ifdef SSD1306_FULLUSE
+	/* for fully used rows just plow thru everything */
+	for (i = 0; i < sizeof(ssd1306_buffer); i += SSD1306_PSZ)
+	{
+		/* send PSZ block of data */
+		ssd1306_data(&ssd1306_buffer[i], SSD1306_PSZ);
+	}
+#else
+	/* for displays with odd rows unused expand bytes */
+	uint8_t tbuf[SSD1306_PSZ], j, k;
+	for (i = 0; i < sizeof(ssd1306_buffer); i += 128) // for each page
+	{
+		/* low nybble */
+		for (j = 0; j < 128; j += SSD1306_PSZ)
+		{
+			for (k = 0; k < SSD1306_PSZ; k++)
+				tbuf[k] = expand[ssd1306_buffer[i + j + k] & 0xf];
+
+			/* send PSZ block of data */
+			ssd1306_data(tbuf, SSD1306_PSZ);
+		}
+
+		/* high nybble */
+		for (j = 0; j < 128; j += SSD1306_PSZ)
+		{
+			for (k = 0; k < SSD1306_PSZ; k++)
+				tbuf[k] = expand[(ssd1306_buffer[i + j + k] >> 4) & 0xf];
+
+			/* send PSZ block of data */
+			ssd1306_data(tbuf, SSD1306_PSZ);
+		}
+	}
+#endif
+}
+
+/*
+ * plot a pixel in the buffer
+ */
+void ssd1306_drawPixel(uint8_t x, uint8_t y, uint8_t color)
+{
+	uint16_t addr;
+
+	/* clip */
+	if (x >= SSD1306_W)
+		return;
+	if (y >= SSD1306_H)
+		return;
+
+	/* compute buffer address */
+	addr = x + SSD1306_W * (y / 8);
+
+	/* set/clear bit in buffer */
+	if (color)
+		ssd1306_buffer[addr] |= (1 << (y & 7));
+	else
+		ssd1306_buffer[addr] &= ~(1 << (y & 7));
+}
+
+/*
+ *  fast vert line
+ */
+void ssd1306_drawFastVLine(uint8_t x, uint8_t y, uint8_t h, uint8_t color)
+{
+	// clipping
+	if ((x >= SSD1306_W) || (y >= SSD1306_H))
+		return;
+	if ((y + h - 1) >= SSD1306_H)
+		h = SSD1306_H - y;
+	while (h--)
+	{
+		ssd1306_drawPixel(x, y++, color);
+	}
+}
+
+/*
+ *  fast horiz line
+ */
+void ssd1306_drawFastHLine(uint8_t x, uint8_t y, uint8_t w, uint8_t color)
+{
+	// clipping
+	if ((x >= SSD1306_W) || (y >= SSD1306_H))
+		return;
+	if ((x + w - 1) >= SSD1306_W)
+		w = SSD1306_W - x;
+
+	while (w--)
+	{
+		ssd1306_drawPixel(x++, y, color);
+	}
+}
+
+/*
+ * abs() helper function for line drawing
+ */
+int16_t gfx_abs(int16_t x)
+{
+	return (x < 0) ? -x : x;
+}
+
+/*
+ * swap() helper function for line drawing
+ */
+void gfx_swap(uint16_t *z0, uint16_t *z1)
+{
+	uint16_t temp = *z0;
+	*z0 = *z1;
+	*z1 = temp;
+}
+
+/*
+ * Bresenham line draw routine swiped from Wikipedia
+ */
+void ssd1306_drawLine(uint16_t x0, uint16_t y0, uint16_t x1, uint16_t y1, uint8_t color)
+{
+	int16_t steep;
+	int16_t deltax, deltay, error, ystep, x, y;
+
+	/* flip sense 45deg to keep error calc in range */
+	steep = (gfx_abs(y1 - y0) > gfx_abs(x1 - x0));
+
+	if (steep)
+	{
+		gfx_swap(&x0, &y0);
+		gfx_swap(&x1, &y1);
+	}
+
+	/* run low->high */
+	if (x0 > x1)
+	{
+		gfx_swap(&x0, &x1);
+		gfx_swap(&y0, &y1);
+	}
+
+	/* set up loop initial conditions */
+	deltax = x1 - x0;
+	deltay = gfx_abs(y1 - y0);
+	error = deltax / 2;
+	y = y0;
+	if (y0 < y1)
+		ystep = 1;
+	else
+		ystep = -1;
+
+	/* loop x */
+	for (x = x0; x <= x1; x++)
+	{
+		/* plot point */
+		if (steep)
+			/* flip point & plot */
+			ssd1306_drawPixel(y, x, color);
+		else
+			/* just plot */
+			ssd1306_drawPixel(x, y, color);
+
+		/* update error */
+		error = error - deltay;
+
+		/* update y */
+		if (error < 0)
+		{
+			y = y + ystep;
+			error = error + deltax;
+		}
+	}
+}
+
+/*
+ *  draws a circle
+ */
+void ssd1306_drawCircle(int16_t x, int16_t y, int16_t radius, int8_t color)
+{
+	/* Bresenham algorithm */
+	int16_t x_pos = -radius;
+	int16_t y_pos = 0;
+	int16_t err = 2 - 2 * radius;
+	int16_t e2;
+
+	do
+	{
+		ssd1306_drawPixel(x - x_pos, y + y_pos, color);
+		ssd1306_drawPixel(x + x_pos, y + y_pos, color);
+		ssd1306_drawPixel(x + x_pos, y - y_pos, color);
+		ssd1306_drawPixel(x - x_pos, y - y_pos, color);
+		e2 = err;
+		if (e2 <= y_pos)
+		{
+			err += ++y_pos * 2 + 1;
+			if (-x_pos == y_pos && e2 <= x_pos)
+			{
+				e2 = 0;
+			}
+		}
+		if (e2 > x_pos)
+		{
+			err += ++x_pos * 2 + 1;
+		}
+	} while (x_pos <= 0);
+}
+
+/*
+ *  draws a filled circle
+ */
+void ssd1306_fillCircle(int16_t x, int16_t y, int16_t radius, int8_t color)
+{
+	/* Bresenham algorithm */
+	int16_t x_pos = -radius;
+	int16_t y_pos = 0;
+	int16_t err = 2 - 2 * radius;
+	int16_t e2;
+
+	do
+	{
+		ssd1306_drawPixel(x - x_pos, y + y_pos, color);
+		ssd1306_drawPixel(x + x_pos, y + y_pos, color);
+		ssd1306_drawPixel(x + x_pos, y - y_pos, color);
+		ssd1306_drawPixel(x - x_pos, y - y_pos, color);
+		ssd1306_drawFastHLine(x + x_pos, y + y_pos, 2 * (-x_pos) + 1, color);
+		ssd1306_drawFastHLine(x + x_pos, y - y_pos, 2 * (-x_pos) + 1, color);
+		e2 = err;
+		if (e2 <= y_pos)
+		{
+			err += ++y_pos * 2 + 1;
+			if (-x_pos == y_pos && e2 <= x_pos)
+			{
+				e2 = 0;
+			}
+		}
+		if (e2 > x_pos)
+		{
+			err += ++x_pos * 2 + 1;
+		}
+	} while (x_pos <= 0);
+}
+
+/*
+ *  draw a rectangle
+ */
+void ssd1306_drawRect(uint8_t x, uint8_t y, uint8_t w, uint8_t h, uint8_t color)
+{
+	ssd1306_drawFastVLine(x, y, h, color);
+	ssd1306_drawFastVLine(x + w - 1, y, h, color);
+	ssd1306_drawFastHLine(x, y, w, color);
+	ssd1306_drawFastHLine(x, y + h - 1, w, color);
+}
+
+/*
+ * fill a rectangle
+ */
+void ssd1306_fillRect(uint8_t x, uint8_t y, uint8_t w, uint8_t h, uint8_t color)
+{
+	uint8_t m, n = y, iw = w;
+
+	/* scan vertical */
+	while (h--)
+	{
+		m = x;
+		w = iw;
+		/* scan horizontal */
+		while (w--)
+		{
+			/* invert pixels */
+			ssd1306_drawPixel(m++, n, color);
+		}
+		n++;
+	}
+}
+
+/*
+ * invert a rectangle in the buffer
+ */
+void ssd1306_xorrect(uint8_t x, uint8_t y, uint8_t w, uint8_t h)
+{
+	uint8_t m, n = y, iw = w;
+
+	/* scan vertical */
+	while (h--)
+	{
+		m = x;
+		w = iw;
+		/* scan horizontal */
+		while (w--)
+		{
+			/* invert pixels */
+			ssd1306_xorPixel(m++, n);
+		}
+		n++;
+	}
+}
+
+/*
+ * initialize I2C and OLED
+ */
+uint8_t ssd1306_init(void)
+{
+	// pulse reset
+	ssd1306_rst();
+
+	// initialize OLED
+	uint8_t *cmd_list = (uint8_t *)ssd1306_init_array;
+	while (*cmd_list != SSD1306_TERMINATE_CMDS)
+	{
+		if (ssd1306_cmd(*cmd_list++))
+			return 1;
+	}
+
+	// clear display
+	// ssd1306_setbuf(0);
+	ssd1306_refresh();
+
+	return 0;
+}
+
+#endif

ssd1306_i2c.h

@@ -0,0 +1,363 @@
+/*
+ * Single-File-Header for SSD1306 I2C interface
+ * 05-07-2023 E. Brombaugh
+ */
+
+#ifndef _SSD1306_I2C_H
+#define _SSD1306_I2C_H
+
+#include <string.h>
+
+// SSD1306 I2C address
+#define SSD1306_I2C_ADDR 0x3c
+
+// I2C Bus clock rate - must be lower the Logic clock rate
+#define SSD1306_I2C_CLKRATE 1000000
+
+// I2C Logic clock rate - must be higher than Bus clock rate
+#define SSD1306_I2C_PRERATE 2000000
+
+// uncomment this for high-speed 36% duty cycle, otherwise 33%
+#define SSD1306_I2C_DUTY
+
+// I2C Timeout count
+#define TIMEOUT_MAX 100000
+
+// uncomment this to enable IRQ-driven operation
+//#define SSD1306_I2C_IRQ
+
+#ifdef SSD1306_I2C_IRQ
+// some stuff that IRQ mode needs
+volatile uint8_t ssd1306_i2c_send_buffer[64], *ssd1306_i2c_send_ptr, ssd1306_i2c_send_sz, ssd1306_i2c_irq_state;
+
+// uncomment this to enable time diags in IRQ
+//#define IRQ_DIAG
+#endif
+
+/*
+ * init just I2C
+ */
+void ssd1306_i2c_setup(void)
+{
+	uint16_t tempreg;
+	
+	// Reset I2C1 to init all regs
+	RCC->APB1PRSTR |= RCC_APB1Periph_I2C1;
+	RCC->APB1PRSTR &= ~RCC_APB1Periph_I2C1;
+	
+	// set freq
+	tempreg = I2C1->CTLR2;
+	tempreg &= ~I2C_CTLR2_FREQ;
+	tempreg |= (FUNCONF_SYSTEM_CORE_CLOCK/SSD1306_I2C_PRERATE)&I2C_CTLR2_FREQ;
+	I2C1->CTLR2 = tempreg;
+	
+	// Set clock config
+	tempreg = 0;
+#if (SSD1306_I2C_CLKRATE <= 100000)
+	// standard mode good to 100kHz
+	tempreg = (FUNCONF_SYSTEM_CORE_CLOCK/(2*SSD1306_I2C_CLKRATE))&SSD1306_I2C_CKCFGR_CCR;
+#else
+	// fast mode over 100kHz
+#ifndef SSD1306_I2C_DUTY
+	// 33% duty cycle
+	tempreg = (FUNCONF_SYSTEM_CORE_CLOCK/(3*SSD1306_I2C_CLKRATE))&SSD1306_I2C_CKCFGR_CCR;
+#else
+	// 36% duty cycle
+	tempreg = (FUNCONF_SYSTEM_CORE_CLOCK/(25*SSD1306_I2C_CLKRATE))&I2C_CKCFGR_CCR;
+	tempreg |= I2C_CKCFGR_DUTY;
+#endif
+	tempreg |= I2C_CKCFGR_FS;
+#endif
+	I2C1->CKCFGR = tempreg;
+
+#ifdef SSD1306_I2C_IRQ
+	// enable IRQ driven operation
+	NVIC_EnableIRQ(I2C1_EV_IRQn);
+	
+	// initialize the state
+	ssd1306_i2c_irq_state = 0;
+#endif
+	
+	// Enable I2C
+	I2C1->CTLR1 |= I2C_CTLR1_PE;
+
+	// set ACK mode
+	I2C1->CTLR1 |= I2C_CTLR1_ACK;
+}
+
+/*
+ * error descriptions
+ */
+char *errstr[] =
+{
+	"not busy",
+	"master mode",
+	"transmit mode",
+	"tx empty",
+	"transmit complete",
+};
+
+/*
+ * error handler
+ */
+uint8_t ssd1306_i2c_error(uint8_t err)
+{
+	// report error
+	printf("ssd1306_i2c_error - timeout waiting for %s\n\r", errstr[err]);
+	
+	// reset & initialize I2C
+	ssd1306_i2c_setup();
+
+	return 1;
+}
+
+// event codes we use
+#define  SSD1306_I2C_EVENT_MASTER_MODE_SELECT ((uint32_t)0x00030001)  /* BUSY, MSL and SB flag */
+#define  SSD1306_I2C_EVENT_MASTER_TRANSMITTER_MODE_SELECTED ((uint32_t)0x00070082)  /* BUSY, MSL, ADDR, TXE and TRA flags */
+#define  SSD1306_I2C_EVENT_MASTER_BYTE_TRANSMITTED ((uint32_t)0x00070084)  /* TRA, BUSY, MSL, TXE and BTF flags */
+
+/*
+ * check for 32-bit event codes
+ */
+uint8_t ssd1306_i2c_chk_evt(uint32_t event_mask)
+{
+	/* read order matters here! STAR1 before STAR2!! */
+	uint32_t status = I2C1->STAR1 | (I2C1->STAR2<<16);
+	return (status & event_mask) == event_mask;
+}
+
+#ifdef SSD1306_I2C_IRQ
+/*
+ * packet send for IRQ-driven operation
+ */
+uint8_t ssd1306_i2c_send(uint8_t addr, uint8_t *data, uint8_t sz)
+{
+	int32_t timeout;
+	
+#ifdef IRQ_DIAG
+	GPIOC->BSHR = (1<<(3));
+#endif
+	
+	// error out if buffer under/overflow
+	if((sz > sizeof(ssd1306_i2c_send_buffer)) || !sz)
+		return 2;
+	
+	// wait for previous packet to finish
+	while(ssd1306_i2c_irq_state);
+	
+#ifdef IRQ_DIAG
+	GPIOC->BSHR = (1<<(16+3));
+	GPIOC->BSHR = (1<<(4));
+#endif
+	
+	// init buffer for sending
+	ssd1306_i2c_send_sz = sz;
+	ssd1306_i2c_send_ptr = ssd1306_i2c_send_buffer;
+	memcpy((uint8_t *)ssd1306_i2c_send_buffer, data, sz);
+	
+	// wait for not busy
+	timeout = TIMEOUT_MAX;
+	while((I2C1->STAR2 & I2C_STAR2_BUSY) && (timeout--));
+	if(timeout==-1)
+		return ssd1306_i2c_error(0);
+
+	// Set START condition
+	I2C1->CTLR1 |= I2C_CTLR1_START;
+
+	// wait for master mode select
+	timeout = TIMEOUT_MAX;
+	while((!ssd1306_i2c_chk_evt(SSD1306_I2C_EVENT_MASTER_MODE_SELECT)) && (timeout--));
+	if(timeout==-1)
+		return ssd1306_i2c_error(1);
+	
+	// send 7-bit address + write flag
+	I2C1->DATAR = addr<<1;
+
+	// wait for transmit condition
+	timeout = TIMEOUT_MAX;
+	while((!ssd1306_i2c_chk_evt(SSD1306_I2C_EVENT_MASTER_TRANSMITTER_MODE_SELECTED)) && (timeout--));
+	if(timeout==-1)
+		return ssd1306_i2c_error(2);
+
+	// Enable TXE interrupt
+	I2C1->CTLR2 |= I2C_CTLR2_ITBUFEN | I2C_CTLR2_ITEVTEN;
+	ssd1306_i2c_irq_state = 1;
+
+#ifdef IRQ_DIAG
+	GPIOC->BSHR = (1<<(16+4));
+#endif
+	
+	// exit
+	return 0;
+}
+
+/*
+ * IRQ handler for I2C events
+ */
+void I2C1_EV_IRQHandler(void) __attribute__((interrupt));
+void I2C1_EV_IRQHandler(void)
+{
+	uint16_t STAR1, STAR2 __attribute__((unused));
+	
+#ifdef IRQ_DIAG
+	GPIOC->BSHR = (1<<(4));
+#endif
+
+	// read status, clear any events
+	STAR1 = I2C1->STAR1;
+	STAR2 = I2C1->STAR2;
+	
+	/* check for TXE */
+	if(STAR1 & I2C_STAR1_TXE)
+	{
+		/* check for remaining data */
+		if(ssd1306_i2c_send_sz--)
+			I2C1->DATAR = *ssd1306_i2c_send_ptr++;
+
+		/* was that the last byte? */
+		if(!ssd1306_i2c_send_sz)
+		{
+			// disable TXE interrupt
+			I2C1->CTLR2 &= ~(I2C_CTLR2_ITBUFEN | I2C_CTLR2_ITEVTEN);
+			
+			// reset IRQ state
+			ssd1306_i2c_irq_state = 0;
+			
+			// wait for tx complete
+			while(!ssd1306_i2c_chk_evt(SSD1306_I2C_EVENT_MASTER_BYTE_TRANSMITTED));
+
+			// set STOP condition
+			I2C1->CTLR1 |= I2C_CTLR1_STOP;
+		}
+	}
+
+#ifdef IRQ_DIAG
+	GPIOC->BSHR = (1<<(16+4));
+#endif
+}
+#else
+/*
+ * low-level packet send for blocking polled operation via i2c
+ */
+uint8_t ssd1306_i2c_send(uint8_t addr, uint8_t *data, uint8_t sz)
+{
+	int32_t timeout;
+	
+	// wait for not busy
+	timeout = TIMEOUT_MAX;
+	while((I2C1->STAR2 & I2C_STAR2_BUSY) && (timeout--));
+	if(timeout==-1)
+		return ssd1306_i2c_error(0);
+
+	// Set START condition
+	I2C1->CTLR1 |= I2C_CTLR1_START;
+	
+	// wait for master mode select
+	timeout = TIMEOUT_MAX;
+	while((!ssd1306_i2c_chk_evt(SSD1306_I2C_EVENT_MASTER_MODE_SELECT)) && (timeout--));
+	if(timeout==-1)
+		return ssd1306_i2c_error(1);
+	
+	// send 7-bit address + write flag
+	I2C1->DATAR = addr<<1;
+
+	// wait for transmit condition
+	timeout = TIMEOUT_MAX;
+	while((!ssd1306_i2c_chk_evt(SSD1306_I2C_EVENT_MASTER_TRANSMITTER_MODE_SELECTED)) && (timeout--));
+	if(timeout==-1)
+		return ssd1306_i2c_error(2);
+
+	// send data one byte at a time
+	while(sz--)
+	{
+		// wait for TX Empty
+		timeout = TIMEOUT_MAX;
+		while(!(I2C1->STAR1 & I2C_STAR1_TXE) && (timeout--));
+		if(timeout==-1)
+			return ssd1306_i2c_error(3);
+		
+		// send command
+		I2C1->DATAR = *data++;
+	}
+
+	// wait for tx complete
+	timeout = TIMEOUT_MAX;
+	while((!ssd1306_i2c_chk_evt(SSD1306_I2C_EVENT_MASTER_BYTE_TRANSMITTED)) && (timeout--));
+	if(timeout==-1)
+		return ssd1306_i2c_error(4);
+
+	// set STOP condition
+	I2C1->CTLR1 |= I2C_CTLR1_STOP;
+	
+	// we're happy
+	return 0;
+}
+#endif
+
+/*
+ * high-level packet send for I2C
+ */
+uint8_t ssd1306_pkt_send(uint8_t *data, uint8_t sz, uint8_t cmd)
+{
+	uint8_t pkt[33];
+	
+	/* build command or data packets */
+	if(cmd)
+	{
+		pkt[0] = 0;
+		pkt[1] = *data;
+	}
+	else
+	{
+		pkt[0] = 0x40;
+		memcpy(&pkt[1], data, sz);
+	}
+	return ssd1306_i2c_send(SSD1306_I2C_ADDR, pkt, sz+1);
+}
+
+/*
+ * init I2C and GPIO
+ */
+uint8_t ssd1306_i2c_init(void)
+{
+	// Enable GPIOC and I2C
+	RCC->APB2PCENR |= RCC_APB2Periph_GPIOC;
+	RCC->APB1PCENR |= RCC_APB1Periph_I2C1;
+	
+	// PC1 is SDA, 10MHz Output, alt func, open-drain
+	GPIOC->CFGLR &= ~(0xf<<(4*1));
+	GPIOC->CFGLR |= (GPIO_Speed_10MHz | GPIO_CNF_OUT_OD_AF)<<(4*1);
+	
+	// PC2 is SCL, 10MHz Output, alt func, open-drain
+	GPIOC->CFGLR &= ~(0xf<<(4*2));
+	GPIOC->CFGLR |= (GPIO_Speed_10MHz | GPIO_CNF_OUT_OD_AF)<<(4*2);
+	
+#ifdef IRQ_DIAG
+	// GPIO diags on PC3/PC4
+	GPIOC->CFGLR &= ~(0xf<<(4*3));
+	GPIOC->CFGLR |= (GPIO_Speed_10MHz | GPIO_CNF_OUT_PP)<<(4*3);
+	GPIOC->BSHR = (1<<(16+3));
+	GPIOC->CFGLR &= ~(0xf<<(4*4));
+	GPIOC->CFGLR |= (GPIO_Speed_10MHz | GPIO_CNF_OUT_PP)<<(4*4);
+	GPIOC->BSHR = (1<<(16+4));
+#endif
+
+	// load I2C regs
+	ssd1306_i2c_setup();
+	
+#if 0
+	// test if SSD1306 is on the bus by sending display off command
+	uint8_t command = 0xAF;
+	return ssd1306_pkt_send(&command, 1, 1);
+#else
+	return 0;
+#endif
+}
+
+/*
+ * reset is not used for SSD1306 I2C interface
+ */
+void ssd1306_rst(void)
+{
+}
+#endif