Check the return value from i2c_smbus_write_byte_data()

README.md

@@ -11,6 +11,8 @@ Raspberry Pi C driver and Python bindings for the sensor BMP180.
 #include "bmp180.h"
 #include <unistd.h>
 #include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
 
 int main(int argc, char **argv){
 	char *i2c_device = "/dev/i2c-1";
@@ -19,11 +21,29 @@ int main(int argc, char **argv){
 	void *bmp = bmp180_init(address, i2c_device);
 
 	if(bmp != NULL){
-		int i;
+		int i, error;
 		for(i = 0; i < 10; i++) {
 			float t = bmp180_temperature(bmp);
+			error = bmp180_get_last_errno(bmp);
+			if (error != 0) {
+				printf("Error reading temperature: %s\n", strerror(error));
+				exit(1);
+			}
+
 			long p = bmp180_pressure(bmp);
+			error = bmp180_get_last_errno(bmp);
+			if (error != 0) {
+				printf("Error reading pressure: %s\n", strerror(error));
+				exit(1);
+			}
+
 			float alt = bmp180_altitude(bmp);
+			error = bmp180_get_last_errno(bmp);
+			if (error != 0) {
+				printf("Error reading altitude: %s\n", strerror(error));
+				exit(1);
+			}
+
 			printf("t = %f, p = %lu, a = %f\n", t, p, alt);
 			usleep(2 * 1000 * 1000);
 		}

src/bmp180.c

@@ -20,6 +20,8 @@
 #include <linux/i2c-dev.h>
 #include <time.h>
 #include <math.h>
+#include <limits.h>
+#include <float.h>
 #endif
 
 
@@ -160,6 +162,9 @@ typedef struct {
 	int32_t mb;
 	int32_t mc;
 	int32_t md;
+
+	/* Last errno */
+	int error;
 } bmp180_t;
 
 
@@ -289,7 +294,13 @@ void bmp180_read_eprom(void *_bmp) {
  */
 int32_t bmp180_read_raw_temperature(void *_bmp) {
 	bmp180_t* bmp = TO_BMP(_bmp);
-	i2c_smbus_write_byte_data(bmp->file, BMP180_CTRL, BMP180_TMP_READ_CMD);
+
+	bmp->error = i2c_smbus_write_byte_data(bmp->file, BMP180_CTRL, BMP180_TMP_READ_CMD);
+	if (bmp->error < 0) {
+		DEBUG("error: i2c_smbus_write_byte_data failed with error %d\n", bmp->error);
+		bmp->error *= -1;
+		return -1;
+	}
 
 	usleep(BMP180_TMP_READ_WAIT_US);
 	int32_t data = i2c_smbus_read_word_data(bmp->file, BMP180_REG_TMP) & 0xFFFF;
@@ -329,7 +340,12 @@ int32_t bmp180_read_raw_pressure(void *_bmp, uint8_t oss) {
 			break;
 	}
 
-	i2c_smbus_write_byte_data(bmp->file, BMP180_CTRL, cmd);
+	bmp->error = i2c_smbus_write_byte_data(bmp->file, BMP180_CTRL, cmd);
+	if (bmp->error < 0) {
+		DEBUG("error: i2c_smbus_write_byte_data failed with error %d\n", bmp->error);
+		bmp->error *= -1;
+		return -1;
+	}
 
 	usleep(wait);
 
@@ -421,6 +437,7 @@ void *bmp180_init(int address, const char* i2c_device_filepath) {
 
 	DEBUG("device: open ok\n");
 
+	bmp->error = 0;
 	return _bmp;
 }
 
@@ -449,6 +466,22 @@ void bmp180_close(void *_bmp) {
 } 
 
 
+/**
+ * Determine if the last BMP180 operation was successful.
+ *
+ * @param bmp180 sensor
+ *
+ * @ret 0 if the last operation was successful; otherwise the errno from the
+ *        last failed operation
+ */
+
+int bmp180_get_last_errno(void *_bmp)
+{
+	bmp180_t* bmp = TO_BMP(_bmp);
+	return bmp->error;
+}
+
+
 /**
  * Returns the measured temperature in celsius.
  * 
@@ -461,6 +494,9 @@ float bmp180_temperature(void *_bmp) {
 	float T;
 
 	UT = bmp180_read_raw_temperature(_bmp);
+	if (bmp->error != 0) {
+		return -FLT_MAX; // error
+	}
 
 	DEBUG("UT=%lu\n",UT);
 
@@ -485,7 +521,14 @@ long bmp180_pressure(void *_bmp) {
 	unsigned long B4, B7;
 
 	UT = bmp180_read_raw_temperature(_bmp);
+	if (bmp->error != 0) {
+		return LONG_MIN; // error
+	}
+
 	UP = bmp180_read_raw_pressure(_bmp, bmp->oss);
+	if (bmp->error != 0) {
+		return LONG_MIN; // error
+	}
 
 	X1 = ((UT - bmp->ac6) * bmp->ac5) >> 15;
 	X2 = (bmp->mc << 11) / (X1 + bmp->md);
@@ -530,8 +573,14 @@ long bmp180_pressure(void *_bmp) {
  * @return altitude
  */
 float bmp180_altitude(void *_bmp) {
+	bmp180_t* bmp = TO_BMP(_bmp);
 	float p, alt;
+
 	p = bmp180_pressure(_bmp);
+	if (bmp->error != 0) {
+		return -FLT_MAX; // error
+	}
+
 	alt = 44330 * (1 - pow(( (p/100) / BMP180_SEA_LEVEL),1/5.255));
 
 	return alt;

src/bmp180.h

@@ -42,5 +42,7 @@ float bmp180_temperature(void *_bmp);
 
 float bmp180_altitude(void *_bmp);
 
+int bmp180_get_last_errno(void *_bmp);
+
 void bmp180_dump_eprom(void *_bmp, bmp180_eprom_t *eprom);
 

src/test.c

@@ -1,6 +1,8 @@
 #include "bmp180.h"
 #include <unistd.h>
 #include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
 
 int main(int argc, char **argv){
 	char *i2c_device = "/dev/i2c-1";
@@ -15,11 +17,29 @@ int main(int argc, char **argv){
 	bmp180_set_oss(bmp, 1);
 
 	if(bmp != NULL){
-		int i;
+		int i, error;
 		for(i = 0; i < 10; i++) {
 			float t = bmp180_temperature(bmp);
+			error = bmp180_get_last_errno(bmp);
+			if (error != 0) {
+				printf("Error reading temperature: %s\n", strerror(error));
+				exit(1);
+			}
+
 			long p = bmp180_pressure(bmp);
+			error = bmp180_get_last_errno(bmp);
+			if (error != 0) {
+				printf("Error reading pressure: %s\n", strerror(error));
+				exit(1);
+			}
+
 			float alt = bmp180_altitude(bmp);
+			error = bmp180_get_last_errno(bmp);
+			if (error != 0) {
+				printf("Error reading altitude: %s\n", strerror(error));
+				exit(1);
+			}
+
 			printf("t = %f, p = %lu, a= %f\n", t, p, alt);
 			usleep(2 * 1000 * 1000);
 		}