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【罗姆传感器评估板试用体验连载】罗姆传感器之Android APK通过i2c总线直接访问气压传感器BM1390GLV

2022-5-24 19:46:38 22383 传感器 Android

0 经过一段时间试用，决定将气压传感器应用到我们Android产品上，成为电子产品的一个实用功能。程序实现方面，Android系统内核是Linux Kernel，常规做法是写一个新I2C设备驱动用来驱动气压传感器，重新编译内核后内核就可以支持气压传感器。不过，这次我决定尝试一种新的做法：从用户空间访问I2C总线，直接和I2C器件进行通讯。这样做的好处显而易见，不需要改kernel代码且无需编译和更新固件，应用程序里就能直接操作I2C设备：气压传感器，编程难度大为降低，代码灵活性大大提高。话不多说，直接上代码： 1. 在用户空间里进行I2C通讯 static char i2c_bus[] = "/dev/i2c-3"; //我的PCBA板子上接的是i2c-3这个总线 static jint i2c_write(uint8_t reg, uint8_t data, int32_t size){ int fd; int ret; unsigned char buf[64]; fd = open(i2c_bus, O_RDWR); LOGI("[i2c_write] Open i2c BUS: %sn", i2c_bus); if (fd < 0) { LOGI("open i2c dev error!n"); return -1; } ret = ioctl(fd, I2C_SLAVE_FORCE, BM1390GLV_DEVICE_ADDRESS); if (ret < 0) { LOGI("set dev error!n"); close(fd); return ret; } memset(buf, 0, 64); write(fd, buf, 10); buf[0] = reg; memcpy(&buf[1], data, size); ret = write(fd, buf, size + 1); if (ret < 0) { LOGI("I2C write error!n"); close(fd); return -1; } close(fd); usleep(1000); return 0; } static jint i2c_read(uint8_t reg, uint8_t data, int32_t size) { int fd; int ret; unsigned char buf[64] = { 0 }; fd = open(i2c_bus, O_RDWR); LOGI("[i2c_read] Open i2c BUS: %sn", i2c_bus); if (fd < 0) { LOGI("open i2c dev error!n"); return BM1390GLV_COMM_ERROR; } ret = ioctl(fd, I2C_SLAVE_FORCE, BM1390GLV_DEVICE_ADDRESS); if (ret < 0) { LOGI("set dev error!n"); close(fd); return ret; } i2c_write(reg, data, size); ret = read(fd, buf, size); if (ret < 0) { LOGI(" I2C read error!n"); close(fd); return BM1390GLV_COMM_ERROR; } memcpy(data, buf, size); close(fd); usleep(1000); return BM1390GLV_COMM_OK; } 2. 初始化传感器 JNIEXPORT jint JNICALL Init(JNIEnv env, jobject thiz) { env->GetJavaVM(&gJavaVM); gJavaObj = env->NewGlobalRef(thiz); int32_t result; result = init_check(); LOGI("Init %d",result); if (result == BM1390GLV_COMM_OK) { (void)init_setting(); } return (result); } static jint init_check(void) { int32_t result; uint8_t id[BM1390GLV_ALL_ID_SIZE]; result = i2c_read(BM1390GLV_MANUFACTURER_ID_PART_ID, id, BM1390GLV_ALL_ID_SIZE); LOGI("init_check %d",result); if (result == BM1390GLV_COMM_OK) { LOGI("id1 %d", id[BM1390GLV_MANUFACTURER_ID]); LOGI("id2 %d", id[BM1390GLV_PART_ID]); if ((id[BM1390GLV_MANUFACTURER_ID] != BM1390GLV_MANUFACTURER_ID_VAL) \|\| (id[BM1390GLV_PART_ID] != BM1390GLV_PART_ID_VAL)) { result = BM1390GLV_WAI_ERROR; } } return (result); } static jint init_setting(void) { int32_t result; uint8_t val; val = BM1390GLV_POWER_DOWN_VAL; result = i2c_write(BM1390GLV_POWER_DOWN, &val, sizeof(val)); if (result == BM1390GLV_COMM_OK) { val = BM1390GLV_RESET_VAL; (void)i2c_write(BM1390GLV_RESET, &val, sizeof(val)); val = BM1390GLV_MODE_CONTROL_VAL; (void)i2c_write(BM1390GLV_MODE_CONTROL, &val, sizeof(val)); ModeCtlVal = val; } return (result); } 3. 读取传感器采集到的气压、温度 static float convert_hpa(uint32_t raw_press) { float press; press = (float)raw_press / BM1390GLV_COUNTS_PER_HPA; return (press); } static jfloat convert_degree_celsius(int16_t raw_temp) { float temp; temp = (float)raw_temp / BM1390GLV_COUNTS_PER_DEGREE_CELSIUS; return (temp); } static jint get_value(uint8_t raw) { int32_t result; result = i2c_read(BM1390GLV_PRESSURE_TEMPERATURE, raw, BM1390GLV_ALL_OUT_SIZE); return (result); } JNIEXPORT jint JNICALL get_val(JNIEnv *env, jobject thi) { int32_t result; uint8_t raw_data[BM1390GLV_ALL_OUT_SIZE]; uint32_t raw_press; uint16_t raw_temp; result = get_value(raw_data); if (result == BM1390GLV_COMM_OK) { raw_press = (uint32_t)raw_data[BM1390GLV_PRESS_OUT_MSB] << 16; raw_press \|= (uint32_t)raw_data[BM1390GLV_PRESS_OUT_LSB] << 8; raw_press \|= (uint32_t)raw_data[BM1390GLV_PRESS_OUT_XL]; raw_temp = (uint16_t)raw_data[BM1390GLV_TEMP_OUT_MSB] << 8; raw_temp \|= (uint16_t)raw_data[BM1390GLV_TEMP_OUT_LSB]; jfloat press = convert_hpa(raw_press); jfloat temp = convert_degree_celsius(raw_temp); LOGI("Pressure(hPa): %f", press); LOGI("Temperature(degree Celsius): %f", temp); }; return (result); } 最后，来看一下效果。先来一张示波器量到的波形，证明用户空间直接通过I2C总线访问I2C器件是成功的：接着看一下通过传感器读取到的气压值和温度值。没有在APK界面上显示，将就一下从PCBA板子的串口看打印信息吧： 0
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