diff --git a/os/ex/ST/hts221.c b/os/ex/ST/hts221.c
new file mode 100644
index 000000000..762478f9b
--- /dev/null
+++ b/os/ex/ST/hts221.c
@@ -0,0 +1,560 @@
+/*
+ ChibiOS - Copyright (C) 2016 Rocco Marco Guglielmi
+
+ This file is part of ChibiOS.
+
+ ChibiOS is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 3 of the License, or
+ (at your option) any later version.
+
+ ChibiOS is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see .
+
+*/
+
+/**
+ * @file hts221.c
+ * @brief HTS221 MEMS interface module code.
+ *
+ * @addtogroup hts221
+ * @{
+ */
+
+#include "hal.h"
+#include "hts221.h"
+
+/*===========================================================================*/
+/* Driver local definitions. */
+/*===========================================================================*/
+
+#define HTS221_SEL(mask, offset) (int16_t)(mask << offset)
+
+/*===========================================================================*/
+/* Driver exported variables. */
+/*===========================================================================*/
+
+/*===========================================================================*/
+/* Driver local variables and types. */
+/*===========================================================================*/
+
+static float hts221_bias[2] = {0.0f, 0.0f};
+static float hts221_sens[2] = {0.0f, 0.0f};
+
+/*===========================================================================*/
+/* Driver local functions. */
+/*===========================================================================*/
+
+#if (HTS221_USE_I2C) || defined(__DOXYGEN__)
+/**
+ * @brief Reads registers value using I2C.
+ * @pre The I2C interface must be initialized and the driver started.
+ *
+ * @param[in] i2cp pointer to the I2C interface
+ * @param[in] reg first sub-register address
+ * @param[out] rxbuf pointer to an output buffer
+ * @return the operation status.
+ * @param[in] n number of consecutive register to read
+ * @notapi
+ */
+msg_t hts221I2CReadRegister(I2CDriver *i2cp, uint8_t reg, uint8_t* rxbuf,
+ size_t n) {
+ uint8_t txbuf = reg;
+ if(n > 1)
+ txbuf |= HTS221_SUB_MS;
+
+ return i2cMasterTransmitTimeout(i2cp, HTS221_SAD, &txbuf, 1, rxbuf, n,
+ TIME_INFINITE);
+}
+
+/**
+ * @brief Writes a value into a register using I2C.
+ * @pre The I2C interface must be initialized and the driver started.
+ *
+ * @param[in] i2cp pointer to the I2C interface
+ * @param[in] txbuf buffer containing sub-address value in first position
+ * and values to write
+ * @param[in] n size of txbuf less one (not considering the first
+ * element)
+ * @return the operation status.
+ * @notapi
+ */
+msg_t hts221I2CWriteRegister(I2CDriver *i2cp, uint8_t* txbuf, size_t n) {
+ if (n > 1)
+ (*txbuf) |= HTS221_SUB_MS;
+
+ return i2cMasterTransmitTimeout(i2cp, HTS221_SAD, txbuf, n + 1, NULL, 0,
+ TIME_INFINITE);
+}
+#endif /* HTS221_USE_I2C */
+
+/**
+ * @brief Compute biases and sensitivities starting from data stored in
+ * calibration registers.
+ * @notapi
+ *
+ * @param[in] dev pointer to the HTS221 interface
+ * @return the operation status.
+ */
+msg_t hts221Calibrate(HTS221Driver *devp) {
+ msg_t msg;
+ uint8_t calib[16], H0_rH_x2, H1_rH_x2, msb;
+ int16_t H0_T0_OUT, H1_T0_OUT, T0_degC_x8, T1_degC_x8, T0_OUT, T1_OUT;
+
+
+#if HTS221_SHARED_I2C
+ i2cAcquireBus(devp->config->i2cp);
+ i2cStart(devp->config->i2cp, devp->config->i2ccfg);
+#endif /* HTS221_SHARED_I2C */
+
+ /* Retrieving rH values from Calibration registers */
+ msg = hts221I2CReadRegister(devp->config->i2cp,
+ HTS221_AD_CALIB_0, calib, 16);
+#if HTS221_SHARED_I2C
+ i2cReleaseBus(devp->config->i2cp);
+#endif /* HTS221_SHARED_I2C */
+
+ H0_rH_x2 = calib[0];
+ H1_rH_x2 = calib[1];
+ H0_T0_OUT = calib[6];
+ H0_T0_OUT += calib[7] << 8;
+ H1_T0_OUT = calib[10];
+ H1_T0_OUT += calib[11] << 8;
+
+ T0_degC_x8 = calib[2];
+ T1_degC_x8 = calib[3];
+
+ /* completing T0_degC_x8 value */
+ msb = (calib[5] & HTS221_SEL(0x03, 0));
+ if(msb & HTS221_SEL(0x01, 1)) {
+ msb |= HTS221_SEL(0x3F, 2);
+ }
+ T0_degC_x8 += msb << 8;
+
+ /* completing T1_degC_x8 value */
+ msb = ((calib[5] & HTS221_SEL(0x03, 2)) >> 2);
+ if(msb & HTS221_SEL(0x01, 1)) {
+ msb |= HTS221_SEL(0x3F, 2);
+ }
+ T1_degC_x8 += msb << 8;
+
+ T0_OUT = calib[12];
+ T0_OUT += calib[13] << 8;
+ T1_OUT = calib[14];
+ T1_OUT += calib[15] << 8;
+
+
+ /* Storing data both in sensor data and in a reference variable used also
+ when user reset bias and sensitivity */
+ hts221_sens[0] = ((float)H1_rH_x2 - (float)H0_rH_x2) /
+ (2.0f * ((float)H1_T0_OUT - (float)H0_T0_OUT));
+ devp->sensitivity[0] = hts221_sens[0];
+
+ hts221_bias[0] = (devp->sensitivity[0] * (float)H0_T0_OUT) -
+ ((float)H0_rH_x2 / 2.0f);
+ devp->bias[0] = hts221_bias[0];
+
+ hts221_sens[1] = ((float)T1_degC_x8 - (float)T0_degC_x8) /
+ (8.0f * ((float)T1_OUT - (float)T0_OUT));
+ devp->sensitivity[1] = hts221_sens[1];
+
+ hts221_bias[1] = (devp->sensitivity[1] * (float)T0_OUT) -
+ ((float)T0_degC_x8 / 8.0f);
+ devp->bias[1] = hts221_bias[1];
+ return msg;
+}
+
+/*
+ * Interface implementation.
+ */
+static size_t hygro_get_axes_number(void *ip) {
+
+ osalDbgCheck(ip != NULL);
+ return HTS221_HYGRO_NUMBER_OF_AXES;
+}
+
+static size_t thermo_get_axes_number(void *ip) {
+
+ osalDbgCheck(ip != NULL);
+ return HTS221_THERMO_NUMBER_OF_AXES;
+}
+
+static size_t sens_get_axes_number(void *ip) {
+
+ osalDbgCheck(ip != NULL);
+ return (thermo_get_axes_number(ip) + hygro_get_axes_number(ip));
+}
+
+static msg_t hygro_read_raw(void *ip, int32_t axis[]) {
+ int16_t tmp;
+ uint8_t buff[2];
+ msg_t msg = MSG_OK;
+
+ osalDbgCheck((ip != NULL) && (axis != NULL));
+ osalDbgAssert((((HTS221Driver *)ip)->state == HTS221_READY),
+ "hygro_read_raw(), invalid state");
+
+ *axis = 0.0f;
+#if HTS221_USE_I2C
+ osalDbgAssert((((HTS221Driver *)ip)->config->i2cp->state == I2C_READY),
+ "hygro_read_raw(), channel not ready");
+#if HTS221_SHARED_I2C
+ i2cAcquireBus(((HTS221Driver *)ip)->config->i2cp);
+ i2cStart(((HTS221Driver *)ip)->config->i2cp,
+ ((HTS221Driver *)ip)->config->i2ccfg);
+#endif /* HTS221_SHARED_I2C */
+
+
+ msg = hts221I2CReadRegister(((HTS221Driver *)ip)->config->i2cp,
+ HTS221_AD_HUMIDITY_OUT_L, buff, 2);
+#if HTS221_SHARED_I2C
+ i2cReleaseBus(((HTS221Driver *)ip)->config->i2cp);
+#endif /* HTS221_SHARED_I2C */
+#endif /* HTS221_USE_I2C */
+
+ if(msg == MSG_OK) {
+ tmp = buff[0] + (buff[1] << 8);
+ *axis = (int32_t)tmp;
+ }
+ return msg;
+}
+
+static msg_t thermo_read_raw(void *ip, int32_t axis[]) {
+ int16_t tmp;
+ uint8_t buff[2];
+ msg_t msg = MSG_OK;
+
+ osalDbgCheck((ip != NULL) && (axis != NULL));
+ osalDbgAssert((((HTS221Driver *)ip)->state == HTS221_READY),
+ "thermo_read_raw(), invalid state");
+ *axis = 0.0f;
+
+#if HTS221_USE_I2C
+ osalDbgAssert((((HTS221Driver *)ip)->config->i2cp->state == I2C_READY),
+ "thermo_read_raw(), channel not ready");
+
+#if HTS221_SHARED_I2C
+ i2cAcquireBus(((HTS221Driver *)ip)->config->i2cp);
+ i2cStart(((HTS221Driver *)ip)->config->i2cp,
+ ((HTS221Driver *)ip)->config->i2ccfg);
+#endif /* HTS221_SHARED_I2C */
+
+ msg = hts221I2CReadRegister(((HTS221Driver *)ip)->config->i2cp,
+ HTS221_AD_TEMP_OUT_L,
+ buff, 2);
+
+#if HTS221_SHARED_I2C
+ i2cReleaseBus(((HTS221Driver *)ip)->config->i2cp);
+#endif /* HTS221_SHARED_I2C */
+#endif /* HTS221_USE_I2C */
+
+ if(msg == MSG_OK) {
+ tmp = buff[0] + (buff[1] << 8);
+ *axis = (int32_t)tmp;
+ }
+ return msg;
+}
+
+static msg_t sens_read_raw(void *ip, int32_t axes[]) {
+ int32_t* bp = axes;
+ msg_t msg;
+ msg = hygro_read_raw(ip, bp);
+ if (msg != MSG_OK){
+ return msg;
+ }
+ bp += HTS221_HYGRO_NUMBER_OF_AXES;
+ return thermo_read_raw(ip, bp);
+}
+
+static msg_t hygro_read_cooked(void *ip, float* axis) {
+ int32_t raw;
+ msg_t msg;
+
+ osalDbgCheck((ip != NULL) && (axis != NULL));
+
+ osalDbgAssert((((HTS221Driver *)ip)->state == HTS221_READY),
+ "hygro_read_cooked(), invalid state");
+
+ msg = hygro_read_raw(ip, &raw);
+
+ *axis = raw * ((HTS221Driver *)ip)->sensitivity[0];
+ *axis -= ((HTS221Driver *)ip)->bias[0];
+ return msg;
+}
+
+static msg_t thermo_read_cooked(void *ip, float* axis) {
+ int32_t raw;
+ msg_t msg;
+
+ osalDbgCheck((ip != NULL) && (axis != NULL));
+
+ osalDbgAssert((((HTS221Driver *)ip)->state == HTS221_READY),
+ "thermo_read_cooked(), invalid state");
+
+ msg = thermo_read_raw(ip, &raw);
+
+ *axis = raw * ((HTS221Driver *)ip)->sensitivity[1];
+ *axis -= ((HTS221Driver *)ip)->bias[1];
+ return msg;
+}
+
+static msg_t sens_read_cooked(void *ip, float axes[]) {
+ float *dp = axes;
+ msg_t msg;
+
+ osalDbgCheck((ip != NULL) && (axes != NULL));
+
+ osalDbgAssert((((HTS221Driver *)ip)->state == HTS221_READY),
+ "sens_read_cooked(), invalid state");
+
+ msg = hygro_read_cooked(ip, dp);
+ if(msg != MSG_OK)
+ return msg;
+ dp += HTS221_THERMO_NUMBER_OF_AXES;
+ return thermo_read_cooked(ip, dp);
+}
+
+static msg_t hygro_set_bias(void *ip, float *bp) {
+ osalDbgCheck((ip != NULL) && (bp != NULL));
+
+ osalDbgAssert((((HTS221Driver *)ip)->state == HTS221_READY) ||
+ (((HTS221Driver *)ip)->state == HTS221_STOP),
+ "thermo_set_bias(), invalid state");
+
+ ((HTS221Driver *)ip)->bias[0] = *bp;
+ return MSG_OK;
+}
+
+static msg_t thermo_set_bias(void *ip, float *bp) {
+ osalDbgCheck((ip != NULL) && (bp != NULL));
+
+ osalDbgAssert((((HTS221Driver *)ip)->state == HTS221_READY) ||
+ (((HTS221Driver *)ip)->state == HTS221_STOP),
+ "thermo_set_bias(), invalid state");
+
+ ((HTS221Driver *)ip)->bias[1] = *bp;
+ return MSG_OK;
+}
+
+static msg_t hygro_reset_bias(void *ip) {
+ osalDbgCheck(ip != NULL);
+
+ osalDbgAssert((((HTS221Driver *)ip)->state == HTS221_READY) ||
+ (((HTS221Driver *)ip)->state == HTS221_STOP),
+ "hygro_reset_bias(), invalid state");
+
+ ((HTS221Driver *)ip)->bias[0] = 0;
+ return MSG_OK;
+}
+
+static msg_t thermo_reset_bias(void *ip) {
+ osalDbgCheck(ip != NULL);
+
+ osalDbgAssert((((HTS221Driver *)ip)->state == HTS221_READY) ||
+ (((HTS221Driver *)ip)->state == HTS221_STOP),
+ "thermo_reset_bias(), invalid state");
+
+ ((HTS221Driver *)ip)->bias[1] = 0;
+ return MSG_OK;
+}
+
+static msg_t hygro_set_sensitivity(void *ip, float *sp) {
+ osalDbgCheck((ip != NULL) && (sp != NULL));
+
+ osalDbgAssert((((HTS221Driver *)ip)->state == HTS221_READY) ||
+ (((HTS221Driver *)ip)->state == HTS221_STOP),
+ "thermo_set_sensitivity(), invalid state");
+
+ ((HTS221Driver *)ip)->sensitivity[0] = *sp;
+ return MSG_OK;
+}
+
+static msg_t thermo_set_sensitivity(void *ip, float *sp) {
+ osalDbgCheck((ip != NULL) && (sp != NULL));
+
+ osalDbgAssert((((HTS221Driver *)ip)->state == HTS221_READY) ||
+ (((HTS221Driver *)ip)->state == HTS221_STOP),
+ "thermo_set_sensitivity(), invalid state");
+
+ ((HTS221Driver *)ip)->sensitivity[1] = *sp;
+ return MSG_OK;
+}
+
+static msg_t hygro_reset_sensitivity(void *ip) {
+ osalDbgCheck(ip != NULL);
+
+ osalDbgAssert((((HTS221Driver *)ip)->state == HTS221_READY) ||
+ (((HTS221Driver *)ip)->state == HTS221_STOP),
+ "hygro_reset_sensitivity(), invalid state");
+
+ ((HTS221Driver *)ip)->sensitivity[0] = HTS221_HYGRO_SENS;
+ return MSG_OK;
+}
+
+static msg_t thermo_reset_sensitivity(void *ip) {
+ osalDbgCheck(ip != NULL);
+
+ osalDbgAssert((((HTS221Driver *)ip)->state == HTS221_READY) ||
+ (((HTS221Driver *)ip)->state == HTS221_STOP),
+ "thermo_reset_sensitivity(), invalid state");
+
+ ((HTS221Driver *)ip)->sensitivity[1] = HTS221_THERMO_SENS;
+ return MSG_OK;
+}
+
+
+static const struct BaseSensorVMT vmt_basesensor = {
+ sens_get_axes_number, sens_read_raw, sens_read_cooked
+};
+
+static const struct BaseHygrometerVMT vmt_basehygrometer = {
+ hygro_get_axes_number, hygro_read_raw, hygro_read_cooked,
+ hygro_set_bias, hygro_reset_bias,
+ hygro_set_sensitivity, hygro_reset_sensitivity
+};
+
+static const struct BaseThermometerVMT vmt_basethermometer = {
+ thermo_get_axes_number, thermo_read_raw, thermo_read_cooked,
+ thermo_set_bias, thermo_reset_bias,
+ thermo_set_sensitivity, thermo_reset_sensitivity
+};
+
+/*===========================================================================*/
+/* Driver exported functions. */
+/*===========================================================================*/
+
+/**
+ * @brief Initializes an instance.
+ *
+ * @param[out] devp pointer to the @p HTS221Driver object
+ *
+ * @init
+ */
+void hts221ObjectInit(HTS221Driver *devp) {
+
+ devp->vmt_basesensor = &vmt_basesensor;
+ devp->vmt_basehygrometer = &vmt_basehygrometer;
+ devp->vmt_basethermometer = &vmt_basethermometer;
+ devp->config = NULL;
+ devp->state = HTS221_STOP;
+ devp->bias[0] = 0.0;
+ devp->bias[1] = 0.0;
+ devp->sensitivity[0] = 0.0;
+ devp->sensitivity[1] = 0.0;
+}
+
+/**
+ * @brief Configures and activates HTS221 Complex Driver peripheral.
+ *
+ * @param[in] devp pointer to the @p HTS221Driver object
+ * @param[in] config pointer to the @p HTS221Config object
+ *
+ * @api
+ */
+void hts221Start(HTS221Driver *devp, const HTS221Config *config) {
+ uint8_t cr[2];
+ osalDbgCheck((devp != NULL) && (config != NULL));
+
+ osalDbgAssert((devp->state == HTS221_STOP) || (devp->state == HTS221_READY),
+ "hts221Start(), invalid state");
+
+ devp->config = config;
+
+#if HTS221_USE_I2C
+#if HTS221_SHARED_I2C
+ i2cAcquireBus((devp)->config->i2cp);
+#endif /* HTS221_SHARED_I2C */
+ i2cStart((devp)->config->i2cp,
+ (devp)->config->i2ccfg);
+
+ /* Control register 1 configuration block.*/
+ {
+ cr[0] = HTS221_AD_CTRL_REG1;
+ cr[1] = devp->config->outputdatarate | HTS221_CTRL_REG1_PD;
+#if HTS221_USE_ADVANCED || defined(__DOXYGEN__)
+ cr[1] |= devp->config->blockdataupdate;
+
+#endif
+ hts221I2CWriteRegister(devp->config->i2cp, cr, 1);
+ }
+
+ /* Average register configuration block.*/
+ {
+ cr[0] = HTS221_AD_AV_CONF;
+ cr[1] = 0x05;
+#if HTS221_USE_ADVANCED || defined(__DOXYGEN__)
+ cr[1] = devp->config->reshumidity | devp->config->restemperature;
+
+#endif
+ hts221I2CWriteRegister(devp->config->i2cp, cr, 1);
+ }
+
+#if HTS221_SHARED_I2C
+ i2cReleaseBus((devp)->config->i2cp);
+#endif /* HTS221_SHARED_I2C */
+#endif /* HTS221_USE_I2C */
+
+ hts221Calibrate(devp);
+
+ if(devp->config->sensitivity != NULL) {
+ /* Taking Sensitivity from user configurations */
+ devp->sensitivity[0] = devp->config->sensitivity[0];
+ devp->sensitivity[1] = devp->config->sensitivity[1];
+ }
+
+ if(devp->config->bias != NULL) {
+ /* Taking Bias from user configurations */
+ devp->bias[0] = devp->config->bias[0];
+ devp->bias[1] = devp->config->bias[1];
+ }
+
+ /* This is the MEMS transient recovery time */
+ osalThreadSleepMilliseconds(5);
+
+ devp->state = HTS221_READY;
+}
+
+/**
+ * @brief Deactivates the HTS221 Complex Driver peripheral.
+ *
+ * @param[in] devp pointer to the @p HTS221Driver object
+ *
+ * @api
+ */
+void hts221Stop(HTS221Driver *devp) {
+ uint8_t cr[2];
+
+ osalDbgCheck(devp != NULL);
+
+ osalDbgAssert((devp->state == HTS221_STOP) || (devp->state == HTS221_READY),
+ "hts221Stop(), invalid state");
+
+#if (HTS221_USE_I2C)
+ if (devp->state == HTS221_STOP) {
+#if HTS221_SHARED_I2C
+ i2cAcquireBus((devp)->config->i2cp);
+ i2cStart((devp)->config->i2cp,
+ (devp)->config->i2ccfg);
+#endif /* HTS221_SHARED_I2C */
+
+ /* Control register 1 configuration block.*/
+ {
+ cr[0] = HTS221_AD_CTRL_REG1;
+ cr[1] = 0;
+ hts221I2CWriteRegister(devp->config->i2cp, cr, 1);
+ }
+
+ i2cStop((devp)->config->i2cp);
+#if HTS221_SHARED_I2C
+ i2cReleaseBus((devp)->config->i2cp);
+#endif /* HTS221_SHARED_I2C */
+ }
+#endif /* HTS221_USE_I2C */
+ devp->state = HTS221_STOP;
+}
+/** @} */
diff --git a/os/ex/ST/hts221.h b/os/ex/ST/hts221.h
new file mode 100644
index 000000000..58c4af956
--- /dev/null
+++ b/os/ex/ST/hts221.h
@@ -0,0 +1,408 @@
+/*
+ ChibiOS - Copyright (C) 2016 Rocco Marco Guglielmi
+
+ This file is part of ChibiOS.
+
+ ChibiOS is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 3 of the License, or
+ (at your option) any later version.
+
+ ChibiOS is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see .
+
+*/
+
+/**
+ * @file hts221.h
+ * @brief HTS221 MEMS interface module header.
+ *
+ * @{
+ */
+#ifndef _HTS221_H_
+#define _HTS221_H_
+
+#include "hal_hygrometer.h"
+#include "hal_thermometer.h"
+
+/*===========================================================================*/
+/* Driver constants. */
+/*===========================================================================*/
+
+/**
+ * @name Version identification
+ * @{
+ */
+/**
+ * @brief HTS221 driver version string.
+ */
+#define EX_HTS221_VERSION "1.0.0"
+
+/**
+ * @brief HTS221 driver version major number.
+ */
+#define EX_HTS221_MAJOR 1
+
+/**
+ * @brief HTS221 driver version minor number.
+ */
+#define EX_HTS221_MINOR 0
+
+/**
+ * @brief HTS221 driver version patch number.
+ */
+#define EX_HTS221_PATCH 0
+/** @} */
+
+/**
+ * @brief HTS221 characteristics.
+ *
+ * @{
+ */
+#define HTS221_HYGRO_NUMBER_OF_AXES 1U
+#define HTS221_THERMO_NUMBER_OF_AXES 1U
+
+#define HTS221_HYGRO_SENS 256.0f /**< LSB/%rH */
+#define HTS221_THERMO_SENS 64.0f /**< LSB/°C */
+/** @} */
+
+/**
+ * @name HTS221 communication interfaces related bit masks
+ * @{
+ */
+#define HTS221_DI_MASK 0xFF /**< Data In mask */
+#define HTS221_DI(n) (1 << n) /**< Data In bit n */
+#define HTS221_AD_MASK 0x3F /**< Address Data mask */
+#define HTS221_AD(n) (1 << n) /**< Address Data bit n */
+#define HTS221_MS (1 << 6) /**< Multiple read write */
+#define HTS221_RW (1 << 7) /**< Read Write selector */
+
+#define HTS221_SUB_MS (1 << 7) /**< Multiple RW in I2C mode*/
+
+#define HTS221_SAD 0x5F /**< Slave Address */
+/** @} */
+
+/**
+ * @name HTS221 register addresses
+ * @{
+ */
+#define HTS221_AD_WHO_AM_I 0x0F
+#define HTS221_AD_AV_CONF 0x10
+#define HTS221_AD_CTRL_REG1 0x20
+#define HTS221_AD_CTRL_REG2 0x21
+#define HTS221_AD_CTRL_REG3 0x22
+#define HTS221_AD_STATUS_REG 0x27
+#define HTS221_AD_HUMIDITY_OUT_L 0x28
+#define HTS221_AD_HUMIDITY_OUT_H 0x29
+#define HTS221_AD_TEMP_OUT_L 0x2A
+#define HTS221_AD_TEMP_OUT_H 0x2B
+#define HTS221_AD_CALIB_0 0x30
+#define HTS221_AD_CALIB_1 0x31
+#define HTS221_AD_CALIB_2 0x32
+#define HTS221_AD_CALIB_3 0x33
+#define HTS221_AD_CALIB_4 0x34
+#define HTS221_AD_CALIB_5 0x35
+#define HTS221_AD_CALIB_6 0x36
+#define HTS221_AD_CALIB_7 0x37
+#define HTS221_AD_CALIB_8 0x38
+#define HTS221_AD_CALIB_9 0x39
+#define HTS221_AD_CALIB_A 0x3A
+#define HTS221_AD_CALIB_B 0x3B
+#define HTS221_AD_CALIB_C 0x3C
+#define HTS221_AD_CALIB_D 0x3D
+#define HTS221_AD_CALIB_E 0x3E
+#define HTS221_AD_CALIB_F 0x3F
+/** @} */
+
+/**
+ * @name HTS221_CTRL_REG1 register bits definitions
+ * @{
+ */
+#define HTS221_CTRL_REG1_MASK 0x87
+#define HTS221_CTRL_REG1_ODR0 (1 << 0)
+#define HTS221_CTRL_REG1_ODR1 (1 << 1)
+#define HTS221_CTRL_REG1_BDU (1 << 2)
+#define HTS221_CTRL_REG1_PD (1 << 7)
+/** @} */
+
+/**
+ * @name HTS221_CTRL_REG2 register bits definitions
+ * @{
+ */
+#define HTS221_CTRL_REG2_MASK 0x83
+#define HTS221_CTRL_REG2_ONE_SHOT (1 << 0)
+#define HTS221_CTRL_REG2_HEATER (1 << 1)
+#define HTS221_CTRL_REG2_BOOT (1 << 7)
+/** @} */
+
+/**
+ * @name HTS221_CTRL_REG3 register bits definitions
+ * @{
+ */
+#define HTS221_CTRL_REG3_MASK 0xC4
+#define HTS221_CTRL_REG3_DRDY (1 << 2)
+#define HTS221_CTRL_REG3_PP_OD (1 << 6)
+#define HTS221_CTRL_REG3_INT_H_L (1 << 7)
+/** @} */
+
+/*===========================================================================*/
+/* Driver pre-compile time settings. */
+/*===========================================================================*/
+
+/**
+ * @name Configuration options
+ * @{
+ */
+/**
+ * @brief HTS221 SPI interface switch.
+ * @details If set to @p TRUE the support for SPI is included.
+ * @note The default is @p FALSE.
+ */
+#if !defined(HTS221_USE_SPI) || defined(__DOXYGEN__)
+#define HTS221_USE_SPI FALSE
+#endif
+
+/**
+ * @brief HTS221 I2C interface switch.
+ * @details If set to @p TRUE the support for I2C is included.
+ * @note The default is @p TRUE.
+ */
+#if !defined(HTS221_USE_I2C) || defined(__DOXYGEN__)
+#define HTS221_USE_I2C TRUE
+#endif
+
+/**
+ * @brief HTS221 advanced configurations switch.
+ * @details If set to @p TRUE more configurations are available.
+ * @note The default is @p FALSE.
+ */
+#if !defined(HTS221_USE_ADVANCED) || defined(__DOXYGEN__)
+#define HTS221_USE_ADVANCED FALSE
+#endif
+
+/**
+ * @brief HTS221 shared I2C switch.
+ * @details If set to @p TRUE the device acquires I2C bus ownership
+ * on each transaction.
+ * @note The default is @p FALSE. Requires I2C_USE_MUTUAL_EXCLUSION
+ */
+#if !defined(HTS221_SHARED_SPI) || defined(__DOXYGEN__)
+#define HTS221_SHARED_I2C FALSE
+#endif
+/** @} */
+
+/*===========================================================================*/
+/* Derived constants and error checks. */
+/*===========================================================================*/
+
+#if !(HTS221_USE_SPI ^ HTS221_USE_I2C)
+#error "HTS221_USE_SPI and HTS221_USE_I2C cannot be both true or both false"
+#endif
+
+#if HTS221_USE_SPI && !HAL_USE_SPI
+#error "HTS221_USE_SPI requires HAL_USE_SPI"
+#endif
+
+#if HTS221_USE_SPI
+#error "HTS221 over SPI still not supported"
+#endif
+
+#if HTS221_USE_I2C && !HAL_USE_I2C
+#error "HTS221_USE_I2C requires HAL_USE_I2C"
+#endif
+
+#if HTS221_SHARED_I2C && !I2C_USE_MUTUAL_EXCLUSION
+#error "HTS221_SHARED_I2C requires I2C_USE_MUTUAL_EXCLUSION"
+#endif
+
+/*
+ * TODO: Add SPI support.
+ */
+
+/*===========================================================================*/
+/* Driver data structures and types. */
+/*===========================================================================*/
+
+/**
+ * @name HTS221 data structures and types.
+ * @{
+ */
+/**
+ * @brief HTS221 output data rate and bandwidth.
+ */
+typedef enum {
+ HTS221_ODR_ONE_SHOT = 0x00, /**< One shot. */
+ HTS221_ODR_1HZ = 0x01, /**< Output data rate 1 Hz. */
+ HTS221_ODR_7HZ = 0x02, /**< Output data rate 7 Hz. */
+ HTS221_ODR_12P5HZ = 0x03, /**< Output data rate 12.5 Hz. */
+}hts221_odr_t;
+
+/**
+ * @brief HTS221 humidity resolution.
+ */
+typedef enum {
+ HTS221_AVGH_4 = 0x00, /**< Number of internal average is 4. */
+ HTS221_AVGH_8 = 0x01, /**< Number of internal average is 8. */
+ HTS221_AVGH_16 = 0x02, /**< Number of internal average is 16. */
+ HTS221_AVGH_32 = 0x03, /**< Number of internal average is 32. */
+ HTS221_AVGH_64 = 0x04, /**< Number of internal average is 64. */
+ HTS221_AVGH_128 = 0x05, /**< Number of internal average is 128. */
+ HTS221_AVGH_256 = 0x06, /**< Number of internal average is 256. */
+ HTS221_AVGH_512 = 0x07 /**< Number of internal average is 512. */
+}hts221_avgh_t;
+
+/**
+ * @brief HTS221 temperature resolution.
+ */
+typedef enum {
+ HTS221_AVGT_2 = 0x00, /**< Number of internal average is 2. */
+ HTS221_AVGT_4 = 0x08, /**< Number of internal average is 4. */
+ HTS221_AVGT_8 = 0x10, /**< Number of internal average is 8. */
+ HTS221_AVGT_16 = 0x18, /**< Number of internal average is 16. */
+ HTS221_AVGT_32 = 0x20, /**< Number of internal average is 32. */
+ HTS221_AVGT_64 = 0x28, /**< Number of internal average is 64. */
+ HTS221_AVGT_128 = 0x30, /**< Number of internal average is 128. */
+ HTS221_AVGT_256 = 0x38, /**< Number of internal average is 256. */
+}hts221_avgt_t;
+
+/**
+ * @brief HTS221 block data update.
+ */
+typedef enum {
+ HTS221_BDU_CONTINUOUS = 0x00, /**< Block data continuously updated. */
+ HTS221_BDU_BLOCKED = 0x40 /**< Block data updated after reading. */
+}hts221_bdu_t;
+
+/**
+ * @brief Driver state machine possible states.
+ */
+typedef enum {
+ HTS221_UNINIT = 0, /**< Not initialized. */
+ HTS221_STOP = 1, /**< Stopped. */
+ HTS221_READY = 2, /**< Ready. */
+} hts221_state_t;
+
+/**
+ * @brief HTS221 configuration structure.
+ */
+typedef struct {
+
+#if HTS221_USE_SPI || defined(__DOXYGEN__)
+ /**
+ * @brief SPI driver associated to this HTS221.
+ */
+ SPIDriver *spip;
+ /**
+ * @brief SPI configuration associated to this HTS221.
+ */
+ const SPIConfig *spicfg;
+#endif /* HTS221_USE_SPI */
+#if HTS221_USE_I2C || defined(__DOXYGEN__)
+ /**
+ * @brief I2C driver associated to this HTS221.
+ */
+ I2CDriver *i2cp;
+ /**
+ * @brief I2C configuration associated to this HTS221.
+ */
+ const I2CConfig *i2ccfg;
+#endif /* HTS221_USE_I2C */
+ /**
+ * @brief HTS221 initial sensitivity.
+ * @note Value are respectively related to hygrometer
+ * and thermometer.
+ */
+ float* sensitivity;
+ /**
+ * @brief HTS221 initial bias.
+ * @note Value are respectively related to hygrometer
+ * and thermometer.
+ */
+ float* bias;
+ /**
+ * @brief HTS221 output data rate selection.
+ */
+ hts221_odr_t outputdatarate;
+#if HTS221_USE_ADVANCED || defined(__DOXYGEN__)
+ /**
+ * @brief HTS221 block data update.
+ */
+ hts221_bdu_t blockdataupdate;
+ /**
+ * @brief HTS221 humidity resolution.
+ */
+ hts221_avgh_t reshumidity;
+ /**
+ * @brief HTS221 temperature resolution.
+ */
+ hts221_avgt_t restemperature;
+#endif
+} HTS221Config;
+
+/**
+ * @brief Structure representing a HTS221 driver.
+ */
+typedef struct HTS221Driver HTS221Driver;
+
+/**
+ * @brief @p HTS221Driver specific data.
+ */
+#define _hts221_data \
+ _base_hygrometer_data \
+ _base_thermometer_data \
+ /* Driver state.*/ \
+ hts221_state_t state; \
+ /* Current configuration data.*/ \
+ const HTS221Config *config; \
+ /* Current sensitivity data.*/ \
+ float sensitivity[HTS221_HYGRO_NUMBER_OF_AXES + \
+ HTS221_THERMO_NUMBER_OF_AXES]; \
+ /* Current Bias data.*/ \
+ float bias[HTS221_HYGRO_NUMBER_OF_AXES + \
+ HTS221_THERMO_NUMBER_OF_AXES];
+
+/**
+ * @extends BaseGyroscope
+ *
+ * @brief HTS221 3-axis barometer class.
+ * @details This class extends @p BaseGyroscope by adding physical
+ * driver implementation.
+ */
+struct HTS221Driver {
+ /** @brief BaseSensor Virtual Methods Table. */
+ const struct BaseSensorVMT *vmt_basesensor;
+ /** @brief BaseHygrometer Virtual Methods Table. */
+ const struct BaseHygrometerVMT *vmt_basehygrometer;
+ /** @brief BaseThermometer Virtual Methods Table. */
+ const struct BaseThermometerVMT *vmt_basethermometer;
+ _hts221_data
+};
+/** @} */
+
+/*===========================================================================*/
+/* Driver macros. */
+/*===========================================================================*/
+
+/*===========================================================================*/
+/* External declarations. */
+/*===========================================================================*/
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+ void hts221ObjectInit(HTS221Driver *devp);
+ void hts221Start(HTS221Driver *devp, const HTS221Config *config);
+ void hts221Stop(HTS221Driver *devp);
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _HTS221_H_ */
+
+/** @} */
+
diff --git a/os/ex/ST/hts221.mk b/os/ex/ST/hts221.mk
new file mode 100644
index 000000000..7e8c8d7e4
--- /dev/null
+++ b/os/ex/ST/hts221.mk
@@ -0,0 +1,6 @@
+# List of all the HTS221 device files.
+HTS221SRC := $(CHIBIOS)/os/ex/ST/hts221.c
+
+# Required include directories
+HTS221INC := $(CHIBIOS)/os/hal/lib/peripherals/sensors \
+ $(CHIBIOS)/os/ex/ST
\ No newline at end of file