diff --git a/Makefile b/Makefile
index d20a631..983f8c7 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,6 @@
 CC=gcc
 OPT=-O2 -std=c99 -Wall -Wextra
+# OPT=-O0 -g3 -std=c99 -Wall -Wextra -pedantic
 CFLAGS=-I. $(OPT)
 CFILES=$(wildcard ./*.c)
 OBJECTS=$(patsubst %.c,%.o, $(CFILES))
diff --git a/bme680.c b/bme680.c
index c5021d6..dd73b01 100644
--- a/bme680.c
+++ b/bme680.c
@@ -1,309 +1,248 @@
 #include "bme680.h"
-#include "i2c.h"
-#include <stdio.h>
+#include "registers.h"
 
-const double const_array1[16] = {
-	1,
-	1,
-	1,
-	1,
-	1,
-	0.99,
-	1, 
-	0.992,
-       	1,
-       	1,
-       	0.998,
-       	0.995, 
-	1,
-       	0.99,
-       	1, 
-	1
+
+
+int bme680_init(bme680_t *bme680) {
+
+	uint8_t car;
+
+	if (bme680->dev.init() != 0) {
+		return 1;
+	}
+
+	if (bme680->dev.read(REG_ID, &car, 1) != 0) {
+		return 1;
+	}
+
+	if (car != 0x61) {
+		return 1;
+	}
+
+	return 0;
+}
+
+
+static double const_array1[16] = {
+	1, 1, 1, 1, 1, 0.99, 1, 0.992, 1,
+       	1, 0.998, 0.995, 1, 0.99, 1, 1
 };
 
-const double const_array2[16] = {
-	8000000,
-       	4000000,
-       	2000000,
-       	1000000,
-       	499500.4995,
-       	248262.1648,
-       	125000,
-	63004.03226, 
-	31281.28128, 
-	15625, 
-	7812.5, 
-	3906.25, 
-	1953.125,
-	976.5625,
-       	488.28125,
-       	244.140625
+static double const_array2[16] = {
+	8000000, 4000000, 2000000, 1000000, 499500.4995, 248262.1648,
+       	125000, 63004.03226, 31281.28128, 15625, 7812.5, 3906.25, 
+	1953.125, 976.5625, 488.28125, 244.140625
 };
 
-const int const_array1_int[16] = {
-	2147483647, 
-	2147483647, 
-	2147483647, 
-	2147483647, 
-	2147483647, 
-	2126008810,
-	2147483647,
-	2130303777,
-	2147483647,
-	2147483647,
-	2143188679,
-	2136746228,
-	2147483647,
-	2126008810,
-	2147483647,
+static int const_array1_int[16] = {
+	2147483647, 2147483647, 2147483647, 2147483647, 2147483647, 
+	2126008810, 2147483647, 2130303777, 2147483647, 2147483647,
+	2143188679, 2136746228, 2147483647, 2126008810, 2147483647,
 	2147483647
 };
 
-const int const_array2_int[16] = {
-	4096000000, // too big ?
-	2048000000,
-	1024000000,
-	512000000,
-	255744255,
-	127110228,
-	64000000,
-	32258064,
-	16016016,
-	8000000,
-	4000000,
-	2000000,
-	1000000,
-	500000,
-	250000,
-	125000
+static int const_array2_int[16] = {
+	4096000000, 2048000000, 1024000000, 512000000, 255744255,
+	127110228, 64000000, 32258064, 16016016, 8000000, 4000000,
+	2000000, 1000000, 500000, 250000, 125000
 };
 
 
-double calc_temp_comp_1 ( uint32_t temp_adc , bme680_t *bme680) {
+static void calc_temp_comp_1 (bme680_t *bme680) {
 
 	double var1, var2, temp_comp;
-	bme680_calibration *cal;
 
-	cal = &bme680->cal;
-
-
-	var1 = (((double)temp_adc / 16384.0) - ((double)cal->par_t1 / 1024.0)) * 
-		(double)cal->par_t2;
-	var2 = ((((double)temp_adc / 131072.0) - ((double)cal->par_t1 / 8192.0)) *
-		(((double)temp_adc / 131072.0) - ((double)cal->par_t1 / 8192.0))) *
-			((double)cal->par_t3 * 16.0);
-	bme680->tfine_double = var1 + var2;
+	var1 = (((double)bme680->adc.temp / 16384.0) - ((double)bme680->cal.par_t1 / 1024.0)) * 
+		(double)bme680->cal.par_t2;
+	var2 = ((((double)bme680->adc.temp / 131072.0) - ((double)bme680->cal.par_t1 / 8192.0)) *
+		(((double)bme680->adc.temp / 131072.0) - ((double)bme680->cal.par_t1 / 8192.0))) *
+			((double)bme680->cal.par_t3 * 16.0);
+	bme680->fcomp.tfine = var1 + var2;
 	temp_comp = (var1 + var2) / 5120.0;
-	bme680->temp_comp_double = temp_comp;
-	return temp_comp;
+	bme680->fcomp.temp = temp_comp;
 }
 
-int calc_temp_comp_2 (uint32_t temp_adc, bme680_t *bme680) {
+static void calc_temp_comp_2 (bme680_t *bme680) {
 
 	int32_t var1, var2, var3, temp_comp;
-	bme680_calibration *cal;
 
-	cal = &bme680->cal;
-
-	var1 = ((int32_t)temp_adc >> 3) - ((int32_t) cal->par_t1 << 1);
-	var2 = (var1 * (int32_t)cal->par_t2) >> 11;
-	var3 = ((((var1 >> 1) * (var1 >> 1)) >> 12) * ((int32_t)cal->par_t3 << 4)) >> 14;
-	bme680->tfine_int = var2 + var3;
-	temp_comp = (( (var2 + var3) * 5) + 128) >> 8;
-	bme680->temp_comp_int = temp_comp;
-	return temp_comp;
+	var1 = ((int32_t)bme680->adc.temp >> 3) - ((int32_t) bme680->cal.par_t1 << 1);
+	var2 = (var1 * (int32_t)bme680->cal.par_t2) >> 11;
+	var3 = ((((var1 >> 1) * (var1 >> 1)) >> 12) * ((int32_t)bme680->cal.par_t3 << 4)) >> 14;
+	bme680->icomp.tfine = var2 + var3;
+	temp_comp = (((var2 + var3) * 5) + 128) >> 8;
+	bme680->icomp.temp = temp_comp;
 }
 
-double calc_press_comp_1 ( uint32_t press_adc  ,  bme680_t *bme680 ) {
+static void calc_press_comp_1 (bme680_t *bme680) {
 
 	double var1, var2, var3, press_comp;
-	bme680_calibration *cal;
 
-	cal = &bme680->cal;
-
-	var1 = ((double)bme680->tfine_double / 2.0) - 64000.0;
-	var2 = var1 * var1 * ((double)cal->par_p6 / 131072.0);
-	var2 = var2 + (var1 * (double)cal->par_p5 * 2.0);
-	var2 = (var2 / 4.0) + ((double)cal->par_p4 * 65536.0);
-	var1 = ((((double)cal->par_p3 * var1 * var1) / 16384.0) +
-		((double)cal->par_p2 * var1)) / 524288.0;
-	var1 = (1.0 + (var1 / 32768.0)) * (double)cal->par_p1;
-	press_comp = 1048576.0 - (double)press_adc;
+	var1 = ((double)bme680->fcomp.tfine / 2.0) - 64000.0;
+	var2 = var1 * var1 * ((double)bme680->cal.par_p6 / 131072.0);
+	var2 = var2 + (var1 * (double)bme680->cal.par_p5 * 2.0);
+	var2 = (var2 / 4.0) + ((double)bme680->cal.par_p4 * 65536.0);
+	var1 = ((((double)bme680->cal.par_p3 * var1 * var1) / 16384.0) +
+		((double)bme680->cal.par_p2 * var1)) / 524288.0;
+	var1 = (1.0 + (var1 / 32768.0)) * (double)bme680->cal.par_p1;
+	press_comp = 1048576.0 - (double)bme680->adc.press;
 	press_comp = ((press_comp - (var2 / 4096.0)) * 6250.0) / var1;
-	var1 = ((double)cal->par_p9 * press_comp * press_comp) / 2147483648.0;
-	var2 = press_comp * ((double)cal->par_p8 / 32768.0);
+	var1 = ((double)bme680->cal.par_p9 * press_comp * press_comp) / 2147483648.0;
+	var2 = press_comp * ((double)bme680->cal.par_p8 / 32768.0);
 	var3 = (press_comp / 256.0) * (press_comp / 256.0) *
-	       (press_comp / 256.0) * (cal->par_p10 / 131072.0);
-	press_comp = press_comp + (var1 + var2 + var3 + ((double)cal->par_p7 * 128.0)) / 16.0;
-
-
-	bme680->press_comp_double = press_comp;
-	return press_comp;
+	       (press_comp / 256.0) * (bme680->cal.par_p10 / 131072.0);
+	press_comp = press_comp + (var1 + var2 + var3 + ((double)bme680->cal.par_p7 * 128.0)) / 16.0;
+	bme680->fcomp.press = press_comp;
 }
 
 
-int calc_press_comp_2  ( uint32_t press_adc ,  bme680_t *bme680 )  {
+static void calc_press_comp_2 (bme680_t *bme680 )  {
 
 	int32_t var1, var2, var3, press_comp;
-	bme680_calibration *cal;
 
-	cal = &bme680->cal;
-
-	var1 = ((int32_t)bme680->tfine_int >> 1) - 64000;
-	var2 = ((((var1 >> 2) * (var1 >> 2)) >> 11) * (int32_t)cal->par_p6) >> 2;
-	var2 = var2 + ((var1 * (int32_t)cal->par_p5) << 1);
-	var2 = (var2 >> 2) + ((int32_t)cal->par_p4 << 16);
+	var1 = ((int32_t)bme680->icomp.tfine >> 1) - 64000;
+	var2 = ((((var1 >> 2) * (var1 >> 2)) >> 11) * (int32_t)bme680->cal.par_p6) >> 2;
+	var2 = var2 + ((var1 * (int32_t)bme680->cal.par_p5) << 1);
+	var2 = (var2 >> 2) + ((int32_t)bme680->cal.par_p4 << 16);
 	var1 = (((((var1 >> 2) * (var1 >> 2)) >> 13) *
-			((int32_t)cal->par_p3 << 5)) >> 3) +  (((int32_t)cal->par_p2 * var1) >> 1);
+			((int32_t)bme680->cal.par_p3 << 5)) >> 3) +  (((int32_t)bme680->cal.par_p2 * var1) >> 1);
 	var1 = var1 >> 18;
-	var1 = ((32768 + var1) * (int32_t)cal->par_p1) >> 15;
-	press_comp = 1048576 - press_adc; // bosch code pg 19 says "press_raw" here ???
+	var1 = ((32768 + var1) * (int32_t)bme680->cal.par_p1) >> 15;
+	press_comp = 1048576 - bme680->adc.press; // bosch code pg 19 says "press_raw" here ???
 	press_comp = (uint32_t)((press_comp - (var2 >> 12)) * ((uint32_t)3125));
 	if (press_comp >= (1 << 30))
 		press_comp = ((press_comp / (uint32_t)var1) << 1);
 	else
 		press_comp = ((press_comp << 1) / (uint32_t)var1);
-	var1 = ((int32_t)cal->par_p9 * (int32_t)(((press_comp >> 3) *
+	var1 = ((int32_t)bme680->cal.par_p9 * (int32_t)(((press_comp >> 3) *
 				(press_comp >> 3)) >> 13)) >> 12;
-	var2 = ((int32_t)(press_comp >> 2) * (int32_t)cal->par_p8) >> 13;
+	var2 = ((int32_t)(press_comp >> 2) * (int32_t)bme680->cal.par_p8) >> 13;
 	var3 = ((int32_t)(press_comp >> 8) * (int32_t)(press_comp >> 8) *
-			(int32_t)(press_comp >> 8) * (int32_t)cal->par_p10) >> 17;
-	press_comp = (int32_t)(press_comp) + ((var1 + var2 + var3 + ((int32_t)cal->par_p7 << 7)) >> 4);
-
-	
-	bme680->press_comp_int = press_comp;
-	
-	return press_comp;
+			(int32_t)(press_comp >> 8) * (int32_t)bme680->cal.par_p10) >> 17;
+	press_comp = (int32_t)(press_comp) + ((var1 + var2 + var3 + ((int32_t)bme680->cal.par_p7 << 7)) >> 4);
+	bme680->icomp.press = press_comp;
 
 }
 
-double calc_hum_comp_1  ( uint32_t hum_adc  ,   bme680_t *bme680 ) {
+static void calc_hum_comp_1 (bme680_t *bme680) {
 	
 	double var1, var2, var3, var4, hum_comp, temp_comp;
-	bme680_calibration *cal;
 
-	cal = &bme680->cal;
-	temp_comp = bme680->temp_comp_double;
+	temp_comp = bme680->fcomp.temp;
 
-	var1 = hum_adc - (((double)cal->par_h1 * 16.0) + (((double)cal->par_h3 / 2.0) * temp_comp));
-	var2 = var1 * (((double)cal->par_h2 / 262144.0) * (1.0 + (((double)cal->par_h4 / 16384.0) *
-				temp_comp) + (((double)cal->par_h5 / 1048576.0) * temp_comp * temp_comp)));
-	var3 = (double)cal->par_h6 / 16384.0;
-	var4 = (double)cal->par_h7 / 2097152.0;
+	var1 = bme680->adc.hum - (((double)bme680->cal.par_h1 * 16.0) + (((double)bme680->cal.par_h3 / 2.0) * temp_comp));
+	var2 = var1 * (((double)bme680->cal.par_h2 / 262144.0) * (1.0 + (((double)bme680->cal.par_h4 / 16384.0) *
+				temp_comp) + (((double)bme680->cal.par_h5 / 1048576.0) * temp_comp * temp_comp)));
+	var3 = (double)bme680->cal.par_h6 / 16384.0;
+	var4 = (double)bme680->cal.par_h7 / 2097152.0;
 	hum_comp = var2 + ((var3 + (var4 * temp_comp)) * var2 * var2);
 
-
-	bme680->hum_comp_double = hum_comp;
-	return hum_comp;
+	bme680->fcomp.hum = hum_comp;
 }
 
 
-int calc_hum_comp_2  (  uint32_t hum_adc  ,  bme680_t *bme680 ) {
+static void calc_hum_comp_2 (bme680_t *bme680) {
 
 	int32_t  var1, var2, var3, var4, var5, var6, temp_scaled, hum_comp;
-	bme680_calibration *cal;
 	
-	cal = &bme680->cal;
-	
-	temp_scaled = (int32_t)bme680->temp_comp_int;
-	var1 = (int32_t)hum_adc - (int32_t)((int32_t)cal->par_h1 << 4) -
-		(((temp_scaled * (int32_t)cal->par_h3) / ((int32_t)100)) >> 1);
-	var2 = ((int32_t)cal->par_h2 * (((temp_scaled * (int32_t)cal->par_h4) / ((int32_t)100)) +
-		(((temp_scaled * ((temp_scaled * (int32_t)cal->par_h5) /
+	temp_scaled = (int32_t)bme680->icomp.temp;
+	var1 = (int32_t)bme680->adc.hum - (int32_t)((int32_t)bme680->cal.par_h1 << 4) -
+		(((temp_scaled * (int32_t)bme680->cal.par_h3) / ((int32_t)100)) >> 1);
+	var2 = ((int32_t)bme680->cal.par_h2 * (((temp_scaled * (int32_t)bme680->cal.par_h4) / ((int32_t)100)) +
+		(((temp_scaled * ((temp_scaled * (int32_t)bme680->cal.par_h5) /
 		((int32_t)100))) >> 6) / ((int32_t)100)) + ((int32_t)(1 << 14)))) >> 10;
 	var3 = var1 * var2;
-	var4 = (((int32_t)cal->par_h6 << 7) +
-			((temp_scaled * (int32_t)cal->par_h7) / ((int32_t)100))) >> 4;
+	var4 = (((int32_t)bme680->cal.par_h6 << 7) +
+			((temp_scaled * (int32_t)bme680->cal.par_h7) / ((int32_t)100))) >> 4;
 	var5 = ((var3 >> 14) * (var3 >> 14)) >> 10;
 	var6 = (var4 * var5) >> 1;
 	hum_comp = (((var3 + var6) >> 10) * ((int32_t) 1000)) >> 12;
 
-
-	bme680->hum_comp_int = hum_comp;
-	return hum_comp;
+	bme680->icomp.hum = hum_comp;
 }
 
-int bme680_calibrate ( int fd , bme680_calibration *cal ) {
+
+int bme680_calibrate(bme680_t *bme680) {
 
 	uint8_t buffer[3] = {0, 0 ,0};
 	int err = 0;
 
 	// start with temp params
 	
-	err |= i2c_read_reg(fd, 0xE9, 2, buffer);
-	cal->par_t1 = (buffer[1] << 8) | buffer[0];
+	err |= bme680->dev.read(0xE9, buffer, 2);
+	bme680->cal.par_t1 = (buffer[1] << 8) | buffer[0];
 
-	err |= i2c_read_reg(fd, 0x8A, 2, buffer);
-	cal->par_t2 = (buffer[1] << 8) | buffer[0];
+	err |= bme680->dev.read(0x8A, buffer, 2);
+	bme680->cal.par_t2 = (buffer[1] << 8) | buffer[0];
 
-	err |= i2c_read_reg(fd, 0x8C, 1, buffer);
-	cal->par_t3 = buffer[0];
+	err |= bme680->dev.read(0x8C, buffer, 1);
+	bme680->cal.par_t3 = buffer[0];
 
 	// pressure
 	
-	err |= i2c_read_reg(fd, 0x8E, 2, buffer);
-	cal->par_p1 = (buffer[1] << 8) | buffer[0];
+	err |= bme680->dev.read(0x8E, buffer, 2);
+	bme680->cal.par_p1 = (buffer[1] << 8) | buffer[0];
 
-	err |= i2c_read_reg(fd, 0x90, 2 , buffer);
-	cal->par_p2 = (buffer[1] << 8) | buffer[0];
+	err |= bme680->dev.read(0x90, buffer, 2);
+	bme680->cal.par_p2 = (buffer[1] << 8) | buffer[0];
 
-	err |= i2c_read_reg(fd, 0x92, 1, buffer);
-	cal->par_p3 = buffer[0];
+	err |= bme680->dev.read(0x92, buffer, 1);
+	bme680->cal.par_p3 = buffer[0];
 
-	err |= i2c_read_reg(fd, 0x94, 2, buffer);
-	cal->par_p4 = (buffer[1] << 8) | buffer[0];
+	err |= bme680->dev.read(0x94, buffer, 2);
+	bme680->cal.par_p4 = (buffer[1] << 8) | buffer[0];
 
-	err |= i2c_read_reg(fd, 0x96, 2, buffer);
-	cal->par_p5 = (buffer[1] << 8) | buffer[0];
+	err |= bme680->dev.read(0x96, buffer, 2);
+	bme680->cal.par_p5 = (buffer[1] << 8) | buffer[0];
 
-	err |= i2c_read_reg(fd, 0x99, 1, buffer);
-	cal->par_p6 = buffer[0];
+	err |= bme680->dev.read(0x99, buffer, 1);
+	bme680->cal.par_p6 = buffer[0];
 
-	err |= i2c_read_reg(fd, 0x98, 1, buffer); // strange order
-	cal->par_p7 = buffer[0];
+	err |= bme680->dev.read(0x98, buffer, 1); // strange order
+	bme680->cal.par_p7 = buffer[0];
 
-	err |= i2c_read_reg(fd, 0x9C, 2, buffer);
-	cal->par_p8 = (buffer[1] << 8) | buffer[0];
+	err |= bme680->dev.read(0x9C, buffer, 1);
+	bme680->cal.par_p8 = (buffer[1] << 8) | buffer[0];
 
-	err |= i2c_read_reg(fd, 0x9E, 2, buffer);
-	cal->par_p9 = (buffer[1] << 8) | buffer[0];
+	err |= bme680->dev.read(0x9E, buffer, 2);
+	bme680->cal.par_p9 = (buffer[1] << 8) | buffer[0];
 
-	err |= i2c_read_reg(fd, 0xA0, 1, buffer);
-	cal->par_p10 = buffer[0];
+	err |= bme680->dev.read(0xA0, buffer, 1);
+	bme680->cal.par_p10 = buffer[0];
 
 	// humidity
 	
-	err |= i2c_read_reg(fd, 0xE2, 2, buffer);
-	cal->par_h1 = (buffer[1] << 4) | (buffer[0] & 0xF);
+	err |= bme680->dev.read(0xE2, buffer, 2);
+	bme680->cal.par_h1 = (buffer[1] << 4) | (buffer[0] & 0xF);
 
-	err |= i2c_read_reg(fd, 0xE1, 2, buffer);
-	cal->par_h2 = (buffer[0] << 4) | ((buffer[1] >> 4) & 0xF);
+	err |= bme680->dev.read(0xE1, buffer, 2);
+	bme680->cal.par_h2 = (buffer[0] << 4) | ((buffer[1] >> 4) & 0xF);
 
-	err |= i2c_read_reg(fd, 0xE4, 1, buffer);
-	cal->par_h3 = buffer[0];
+	err |= bme680->dev.read(0xE4, buffer, 1);
+	bme680->cal.par_h3 = buffer[0];
 
-	err |= i2c_read_reg(fd, 0xE5, 1, buffer);
-	cal->par_h4 = buffer[0];
+	err |= bme680->dev.read(0xE5, buffer, 1);
+	bme680->cal.par_h4 = buffer[0];
 
-	err |= i2c_read_reg(fd, 0xE6, 1, buffer);
-	cal->par_h5 = buffer[0];
+	err |= bme680->dev.read(0xE6, buffer, 1);
+	bme680->cal.par_h5 = buffer[0];
 
-	err |= i2c_read_reg(fd, 0xE7, 1, buffer);
-	cal->par_h6 = buffer[0];
+	err |= bme680->dev.read(0xE7, buffer, 1);
+	bme680->cal.par_h6 = buffer[0];
 
-	err |= i2c_read_reg(fd, 0xE8, 1, buffer);
-	cal->par_h7 = buffer[0];
+	err |= bme680->dev.read(0xE8, buffer, 1);
+	bme680->cal.par_h7 = buffer[0];
 
 	// gas
 	
-	err |= i2c_read_reg(fd, 0xED, 1, buffer);
-	cal->par_g1 = buffer[0];
+	err |= bme680->dev.read(0xED, buffer, 1);
+	bme680->cal.par_g1 = buffer[0];
 
-	err |= i2c_read_reg(fd, 0xEB, 2, buffer);
-	cal->par_g2 = (buffer[1] << 8) | buffer[0];
+	err |= bme680->dev.read(0xEB, buffer, 2);
+	bme680->cal.par_g2 = (buffer[1] << 8) | buffer[0];
 
-	err |= i2c_read_reg(fd, 0xEE, 1, buffer);
-	cal->par_g2 = buffer[0];
+	err |= bme680->dev.read(0xEE, buffer, 1);
+	bme680->cal.par_g2 = buffer[0];
 
 	//  todo more
 
@@ -312,6 +251,7 @@ int bme680_calibrate ( int fd , bme680_calibration *cal ) {
 	return err;
 }
 
+/*
 void print_calibration  ( bme680_calibration *cal ) {
 	printf("par_t1: %d\n", cal->par_t1);
 	printf("par_t2: %d\n", cal->par_t2);
@@ -333,4 +273,6 @@ void print_calibration  ( bme680_calibration *cal ) {
 	printf("par_h5: %d\n", cal->par_h5);
 	printf("par_h6: %d\n", cal->par_h6);
 	printf("par_h7: %d\n", cal->par_h7);
-}
+} */
+
+
diff --git a/bme680.h b/bme680.h
index 62fea15..a89081a 100644
--- a/bme680.h
+++ b/bme680.h
@@ -1,64 +1,128 @@
-#pragma once
+#ifndef BME680_H
+#define BME680
 
 #include <stdint.h>
 
-typedef struct {
+/* connection modes */
+#define BME680_SPI   1
+#define BME680_I2C   0
 
+/* calculation modes; int or float calc */
+#define BME680_MODE_INT   2
+#define BME680_MODE_FLOAT 0
+
+#define BME680_MAX_XFER_SIZE 128
+
+/* config values */
+#define BME680_OVERSAMPLE_1X  0b001
+#define BME680_OVERSAMPLE_2X  0b010
+#define BME680_OVERSAMPLE_4X  0b011
+#define BME680_OVERSAMPLE_8X  0b100
+#define BME680_OVERSAMPLE_16X 0b101
+
+/* IIR filter */
+#define BME680_IIR_COEFF_0   0b000
+#define BME680_IIR_COEFF_1   0b001
+#define BME680_IIR_COEFF_3   0b010
+#define BME680_IIR_COEFF_7   0b011
+#define BME680_IIR_COEFF_15  0b100
+#define BME680_IIR_COEFF_31  0b101
+#define BME680_IIR_COEFF_63  0b110
+#define BME680_IIR_COEFF_127 0b111
+
+
+/* user supplied spi/i2c functions */
+struct bme680_dev {
+	int (*init)   (void);
+	int (*read)   (uint8_t reg, uint8_t *dst, uint32_t size);
+	int (*write)  (uint8_t reg, uint8_t *src, uint32_t size);
+	int (*xfer)   (uint8_t reg, uint8_t *src, uint8_t *dst, uint32_t size);
+	int (*deinit) (void);
+};
+
+struct bme680_cal {
+	/* temp calibration */
 	uint16_t par_t1;
-	int16_t par_t2;
-	int8_t par_t3;
+	int16_t  par_t2;
+	int8_t   par_t3;
 
+	/* press calibration */
 	uint16_t par_p1;
-	int16_t par_p2;
-	int8_t par_p3; 
-	int16_t par_p4;
-	int16_t par_p5;
-	int8_t par_p6; 
-	int8_t par_p7; 
-	int16_t par_p8; 
-	int16_t par_p9;
-	uint8_t par_p10;
+	int16_t  par_p2;
+	int8_t   par_p3; 
+	int16_t  par_p4;
+	int16_t  par_p5;
+	int8_t   par_p6; 
+	int8_t   par_p7; 
+	int16_t  par_p8; 
+	int16_t  par_p9;
+	uint8_t  par_p10;
 
+	/* humidity calibration */
 	uint16_t par_h1; 
 	uint16_t par_h2;
-	int8_t par_h3;
-	int8_t par_h4;
-	int8_t par_h5;
-	uint8_t par_h6;
-	int8_t par_h7;
+	int8_t   par_h3;
+	int8_t   par_h4;
+	int8_t   par_h5;
+	uint8_t  par_h6;
+	int8_t   par_h7;
 
+	/* gas maybe */
 	uint16_t par_g1;
 	uint16_t par_g2;
 	uint16_t par_g3;
 	uint16_t range_switching_error;
-} bme680_calibration;
+};
 
-typedef struct {
 
-	int tfine_int;
-	double tfine_double;
+struct bme680_config {
+	uint8_t osrs_t;
+	uint8_t osrs_p;
+	uint8_t osrs_h;
+	uint8_t fir;
+	uint8_t heater_setpoint[10];
+	uint8_t heater_exposure_ms[10];
+	uint8_t heater_exposure_scalar[10];
+};
 
-	double temp_comp_double;
-	int temp_comp_int;
+struct bme680_comp_float {
+	double tfine;
+	double temp;
+	double press;
+	double hum;
+};
 
-	double press_comp_double;
-	int press_comp_int;
+struct bme680_comp_int {
+	int32_t tfine;
+	int32_t temp;
+	int32_t press;
+	int32_t hum;
+};
 
-	double hum_comp_double;
-	int hum_comp_int;
+struct bme680_adc {
+	uint32_t temp;
+	uint32_t press;
+	uint32_t hum;
+	uint16_t gas;
+};
 
-	bme680_calibration cal;
+struct bme680 {
+	struct bme680_comp_float fcomp;
+	struct bme680_comp_int   icomp;
+	struct bme680_cal cal;
+	struct bme680_dev dev;
+	struct bme680_config cfg;
+	struct bme680_adc adc;
+	uint8_t mode;
+};
 
-} bme680_t;
+typedef struct bme680 bme680_t;
+
+
+int bme680_init(bme680_t *bme680);
+int bme680_calibrate(bme680_t *bme680);
 
 
 
-void print_calibration(bme680_calibration *);
-int bme680_calibrate(int, bme680_calibration *);
-int calc_hum_comp_2(uint32_t, bme680_t *);
-int calc_press_comp_2(uint32_t, bme680_t *);
-int calc_temp_comp_2(uint32_t, bme680_t *);
-double calc_temp_comp_1(uint32_t, bme680_t*);
-double calc_press_comp_1(uint32_t, bme680_t *);
-double calc_hum_comp_1(uint32_t, bme680_t *);
 
+#endif
diff --git a/bst-bme680-ds001.pdf b/bst-bme680-ds001.pdf
new file mode 100644
index 0000000..3be3044
Binary files /dev/null and b/bst-bme680-ds001.pdf differ
diff --git a/main.c b/main.c
index 1fa69ce..83c8f0c 100644
--- a/main.c
+++ b/main.c
@@ -2,94 +2,94 @@
 #define _DEFAULT_SOURCE
 
 #include <stdio.h>
+#include <stdlib.h>
 #include <unistd.h>
+
 #include "bme680.h"
 #include "i2c.h"
 
 #define DEVICE "/dev/i2c-1"
 #define ADDRESS 0x77
 
+int i2c_dev_fd;
+
+int linux_i2c_init   (void);
+int linux_i2c_read   (uint8_t reg, uint8_t *dst, uint32_t size);
+int linux_i2c_write  (uint8_t reg, uint8_t *src, uint32_t size);
+int linux_i2c_deinit (void);
+
 int main(){
 	
-	int fd = i2c_init(DEVICE, ADDRESS);
 	bme680_t bme680;
 
-	printf("%X\n", i2c_read_reg2(fd, 0xD0));
-	if (bme680_calibrate(fd, &bme680.cal) != 0) {
-	       fprintf(stderr, "error bme680 calibration\n");
-	} else {
- 		print_calibration(&bme680.cal);
-	}		
+	/* 1. Assign functions for interacting with the device */
+	bme680.dev.init = linux_i2c_init;	
+	bme680.dev.read = linux_i2c_read;
+	bme680.dev.write = linux_i2c_write;
+	bme680.dev.deinit = linux_i2c_deinit;
+	bme680.dev.xfer = NULL;
+
+	/* 2. set the device mode */
+	bme680.mode = BME680_MODE_FLOAT | BME680_I2C;
+	/*            BME680_MODE_INT   | BME680_SPI; */
 
 
-
-	//1. write osrs fields to diff regs
-	uint8_t ctrl_meas, ctrl_hum;
-
-	uint8_t osrs_t, osrs_p, osrs_h, ctrl_mode;
-	osrs_t = osrs_p = osrs_h = 0b110;
-	ctrl_mode = 0;
-
-	ctrl_meas = (osrs_t << 5) | (osrs_p << 2) | ctrl_mode;
-	ctrl_hum = osrs_h;
-
-	i2c_write_reg(fd, 0x74, ctrl_meas);
-	i2c_write_reg(fd, 0x72, ctrl_hum);
-
-	// set filter mode 
-	
-	uint8_t filter_reg = 0b101 << 2;
-	i2c_write_reg(fd, 0x75, filter_reg);
-	
-	// todo gas stuff
-	
-	// resend ctrl_meas but with ctrl_mode set to 0b01 in it, then it should work
-	ctrl_meas |= 1;
-	i2c_write_reg(fd,  0x74, ctrl_meas);
-
-	// poll reg `meas_status_0 bit 5. It will be 0 when all scheduled conversions are done.
-	uint8_t qq;
-	while ((qq = i2c_read_reg2(fd, 0x1D)) >> 4) {
-		usleep(2000); // 2 ms
+	/* 3. initialise device, and check its id */
+	if (bme680_init(&bme680) != 0) {
+		fprintf(stderr, "bme680_init()\n");
+		exit(EXIT_FAILURE);
 	}
 
-	// now read the temp/press/hum adc and convert in order.
-	uint32_t temp_adc, press_adc, hum_adc;
+	/* 4. read calibration parameters from the device and store in memory */
+	if (bme680_calibrate(&bme680) != 0) {
+		fprintf(stderr, "bme680_calibrate()\n");
+		bme680.dev.deinit();
+		exit(EXIT_FAILURE);
+	}
+
+	/* 5. set up device config */
+	bme680.cfg.osrs_t = BME680_OVERSAMPLE_16X;
+	bme680.cfg.osrs_p = BME680_OVERSAMPLE_8X;
+	bme680.cfg.osrs_h = BME680_OVERSAMPLE_4X;
 
 
-	uint8_t buffer[3];
-
-	i2c_read_reg(fd, 0x22, 3, buffer);
-	temp_adc = (buffer[0] << 12) | (buffer[1] << 4) | (buffer[2] >> 4);
-
-	i2c_read_reg(fd, 0x1F, 3, buffer);
-	press_adc = (buffer[0] << 12) | (buffer[1] << 4) | (buffer[2] >> 4);
-
-	i2c_read_reg(fd, 0x25, 2, buffer);
-	hum_adc = (buffer[0] << 8) | buffer[1];
-
-	// adc readings are only 20-bit when the IIR filter is enabled, otherwise
-	// the size depends on the oversample settings (osrs_X).
-	
-	double temperature = calc_temp_comp_1 ( temp_adc ,  &bme680 );
-	printf("temperature: %g oC (floating-point)\n", temperature);
-	
-	int temperature2 = calc_temp_comp_2 (temp_adc,  &bme680 );
-	printf("temperature: %d oC (integer x100)\n", temperature2);
 
 
-	double pressure = calc_press_comp_1 ( press_adc  , &bme680 );
-	printf("pressure: %g Pa or %g bar (floating-point)\n", pressure, pressure/1e5);
-
-	int pressure2 = calc_press_comp_2 (press_adc  ,  &bme680 );
-	printf("pressure: %d Pa (integer)\n", pressure2);
-
-	double humidity = calc_hum_comp_1 ( hum_adc, &bme680 );
-	printf("humidity: %g (floating-point)\n", humidity);
-
-	int humidity2 = calc_hum_comp_2 ( hum_adc,  &bme680 );
-	printf("humidity: %d (integer x1000)\n", humidity2);
-
-	close(fd);
+	return 0;
+}
+
+// STUBS
+
+int linux_i2c_init (void) {
+	puts("linux_i2c_init");
+	int ret = i2c_init(DEVICE, ADDRESS);
+	if (ret > 0) {
+		i2c_dev_fd = ret;
+		return 0;
+	}
+
+	return 1;
+}
+
+int linux_i2c_read (uint8_t reg, uint8_t *dst, uint32_t size) {
+	puts("linux_i2c_read");
+	if (i2c_read_reg(i2c_dev_fd, reg, (uint8_t)size, dst) != 0) {
+		printf("panic read: %d %p %d\n", reg, dst, size);
+		return 1;
+	}
+	return 0;
+}
+
+int linux_i2c_write (uint8_t reg, uint8_t *src, uint32_t size) {
+	puts("linux_i2c_write");
+	if (i2c_write_reg(i2c_dev_fd, reg, *src) != 0) {
+		puts("panic!");
+		return 1;
+	}
+	return 0;
+}
+
+int linux_i2c_deinit (void) {
+	close(i2c_dev_fd);
 	return 0;
 }
diff --git a/registers.h b/registers.h
new file mode 100644
index 0000000..1566ec3
--- /dev/null
+++ b/registers.h
@@ -0,0 +1,67 @@
+#ifndef REGISTERS_H
+#define REGISTERS_H
+
+#define REG_SPI_PAGE(v) ((v > 0x7F) ? 0 : 1)
+
+#define REG_STATUS      0x73
+#define REG_RESET       0xE0
+#define REG_ID          0xD0
+#define REG_CONFIG      0x75
+#define REG_CTRL_MEAS   0x74
+#define REG_CTRL_HUM    0x72
+
+#define REG_CTRL_GAS_1  0x71
+#define REG_CTRL_GAS_0  0x70
+
+#define REG_GAS_WAIT_9  0x6D
+#define REG_GAS_WAIT_8  0x6C
+#define REG_GAS_WAIT_7  0x6B
+#define REG_GAS_WAIT_6  0x6A
+#define REG_GAS_WAIT_5  0x69
+#define REG_GAS_WAIT_4  0x68
+#define REG_GAS_WAIT_3  0x67
+#define REG_GAS_WAIT_2  0x66
+#define REG_GAS_WAIT_1  0x65
+#define REG_GAS_WAIT_0  0x64
+
+#define REG_RES_HEAT_9  0x63
+#define REG_RES_HEAT_8  0x62
+#define REG_RES_HEAT_7  0x61
+#define REG_RES_HEAT_6  0x60
+#define REG_RES_HEAT_5  0x5F
+#define REG_RES_HEAT_4  0x5E
+#define REG_RES_HEAT_3  0x5D
+#define REG_RES_HEAT_2  0x5C
+#define REG_RES_HEAT_1  0x5B
+#define REG_RES_HEAT_0  0x5A
+
+#define REG_IDAC_HEAT_9 0x59
+#define REG_IDAC_HEAT_8 0x58
+#define REG_IDAC_HEAT_7 0x57
+#define REG_IDAC_HEAT_6 0x56
+#define REG_IDAC_HEAT_5 0x55
+#define REG_IDAC_HEAT_4 0x54
+#define REG_IDAC_HEAT_3 0x53
+#define REG_IDAC_HEAT_2 0x52
+#define REG_IDAC_HEAT_1 0x51
+#define REG_IDAC_HEAT_0 0x50
+
+#define REG_GAS_R_LSB   0x2B
+#define REG_GAS_R_MSB   0x2A
+
+#define REG_HUM_LSB     0x26
+#define REG_HUM_MSB     0x25
+
+#define REG_TEMP_XLSB   0x24
+#define REG_TEMP_LSB    0x23
+#define REG_TEMP_MSB    0x22
+
+#define REG_PRESS_XLSB  0x21
+#define REG_PRESS_LSB   0x20
+#define REG_PRESS_MSB   0x1F
+
+#define REG_EAS_STATUS  0x1D
+
+
+
+#endif