diff --git a/mbtk/mbtk_gnssd/gnss_hd8122.c b/mbtk/mbtk_gnssd/gnss_hd8122.c
index dc36267..57b2e30 100755
--- a/mbtk/mbtk_gnssd/gnss_hd8122.c
+++ b/mbtk/mbtk_gnssd/gnss_hd8122.c
@@ -27,10 +27,91 @@
 
 #define UART_BITRATE_NMEA_DEF_FW    115200   // Default bitrate.
 #define GNSS_POWER_GPIO 43
+#define GNSS_SET_TIMEOUT           3000     // 3s
+#define GNSS_PACK_BUFF_SIZE           1024
+
 
 static pthread_cond_t read_cond;
 static pthread_mutex_t read_mutex;
+static bool setting_busy = FALSE;
+static void *gnss_set_rsp_ptr = NULL;
+static gnss_err_enum gnss_set_result = GNSS_ERR_OK;
 
+int gnss_write(int fd, const void *data, int data_len);
+
+static uint16 fletcher16(const uint8_t* data, int data_len) {
+    uint16_t sum1 = 0;
+    uint16_t sum2 = 0;
+    int index;
+
+    for (index = 0; index < data_len; ++index ) {
+        sum1 = (sum1 + data[index]) % 0xff;
+        sum2 = (sum2 + sum1) % 0xff;
+    }
+
+    // ???
+    sum2--;
+
+    return (sum2 << 8) | sum1;
+}
+
+static void gnss_set_timer_cb(int signo)
+{
+    if(setting_busy) {
+        pthread_mutex_lock(&read_mutex);
+        pthread_cond_signal(&read_cond);
+        pthread_mutex_unlock(&read_mutex);
+        gnss_set_result = GNSS_ERR_TIMEOUT;
+    }
+    return;
+}
+
+
+static int pack_create(hd8122_id_type_enum id_type, uint8 id, uint16 data_len, const uint8 *data, uint8 *pack, int pack_len)
+{
+    if(pack == NULL || pack_len < HD8122_PACK_LEN_MIN) {
+        return -1;
+    }
+    memset(pack, 0, pack_len);
+    uint8 *data_ptr = pack;
+    data_ptr += uint16_2_byte(HD8122_PACK_HEAD, data_ptr, false);
+    *data_ptr++ = (uint8)id_type;
+    *data_ptr++ = id;
+    data_ptr += uint16_2_byte(data_len, data_ptr, false);
+    if(data_len > 0) {
+        memcpy(data_ptr, data, data_len);
+        data_ptr += data_len;
+    }
+    data_ptr += uint16_2_byte(fletcher16(pack + 2, 4 + data_len), data_ptr, false);
+    return (data_ptr - pack);
+}
+
+static void gnss_cmd_rsp_process(const void *data, int data_len) {
+    const char *ptr = (const char*)data;
+    log_hex("RSP", data, data_len);
+    if(0)
+    {
+        mbtk_timer_clear();
+
+        pthread_mutex_lock(&read_mutex);
+        pthread_cond_signal(&read_cond);
+        pthread_mutex_unlock(&read_mutex);
+    }
+}
+
+static gnss_err_enum gnss_8122_reset(int fd, int reset)
+{
+    uint8 buff[GNSS_PACK_BUFF_SIZE];
+    LOGD("RESET");
+    int len = pack_create(HD8122_ID_TYPE_CFG, HD8122_ID_CFG_SIMPLERST, 1, (uint8*)(&reset), buff, sizeof(buff));
+    if(len <= 0) {
+        LOGE("pack_create() fail.");
+        return GNSS_ERR_ARG;
+    }
+    log_hex("PACK", buff, len);
+    gnss_write(fd, buff, len);
+    return GNSS_ERR_OK;
+}
 
 int gnss_8122_dev_open()
 {
@@ -61,9 +142,55 @@
     return 0;
 }
 
+void gnss_8122_set_cb(const void *data, int data_len)
+{
+    const char *buff = (const char*)data;
+    if(setting_busy) {
+        gnss_cmd_rsp_process(data, data_len);
+    }
+}
 
 gnss_err_enum gnss_8122_set(int fd, const char *cmd, void *cmd_rsp, int cmd_rsp_len)
 {
-    return GNSS_ERR_OK;
+    if(setting_busy) {
+        return GNSS_ERR_SET_BUSY;
+    } else {
+        bool should_wait_rsp = TRUE;
+        setting_busy = TRUE;
+        gnss_set_rsp_ptr = cmd_rsp;
+        gnss_set_result = GNSS_ERR_OK;
+        mbtk_timer_set(gnss_set_timer_cb, GNSS_SET_TIMEOUT);
+
+        if(memcmp(cmd, "reset", 5) == 0) {
+            gnss_set_result = gnss_8122_reset(fd, atoi(cmd + 6));
+            if(gnss_set_result != GNSS_ERR_OK) {
+                goto set_fail;
+            }
+            should_wait_rsp = FALSE;
+        }
+        else
+        {
+            LOGW("Unknown cmd:%s", cmd);
+            gnss_set_result = GNSS_ERR_UNSUPPORT;
+            goto set_fail;
+        }
+
+set_success:
+        if(should_wait_rsp) {
+            pthread_mutex_lock(&read_mutex);
+            pthread_cond_wait(&read_cond, &read_mutex);
+            pthread_mutex_unlock(&read_mutex);
+        } else {
+            mbtk_timer_clear();
+        }
+
+        setting_busy = FALSE;
+        return gnss_set_result;
+set_fail:
+        setting_busy = FALSE;
+        mbtk_timer_clear();
+        return gnss_set_result;
+    }
 }
 
+