Update documentation and fix small issues.

examples/sht21/CMakeLists.txt

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+# Copyright 2017 Rafal Zajac <rzajac@gmail.com>.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+
+find_package(esp_sdo REQUIRED)
+find_package(esp_i2c REQUIRED)
+find_package(esp_util REQUIRED)
+
+add_executable(sht21_ex main.c ${ESP_USER_CONFIG})
+
+target_include_directories(sht21_ex PUBLIC
+    ${ESP_USER_CONFIG_DIR}
+    ${esp_sdo_INCLUDE_DIRS}
+    ${esp_i2c_INCLUDE_DIRS}
+    ${esp_util_INCLUDE_DIRS})
+
+target_link_libraries(sht21_ex
+    ${esp_sdo_LIBRARIES}
+    ${esp_i2c_LIBRARIES}
+    ${esp_util_LIBRARIES}
+    esp_sht21)
+
+esp_gen_exec_targets(sht21_ex)

examples/sht21/README.md

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+## SHT21 example.
+
+Demonstrates how to:
+- get serial number,
+- get firmware version,
+- get humidity and temperature.
+
+## Flashing
+
+```
+$ cd build
+$ cmake ..
+$ make sht21_ex_flash
+$ miniterm.py /dev/ttyUSB0 74880
+```

examples/sht21/main.c

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+/*
+ * Copyright 2017 Rafal Zajac <rzajac@gmail.com>.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License. You may obtain
+ * a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ */
+
+
+#include <esp_sht21.h>
+#include <esp_sdo.h>
+#include <esp_util.h>
+#include <user_interface.h>
+
+#define SCL GPIO0
+#define SDA GPIO2
+
+os_timer_t timer;
+
+void ICACHE_FLASH_ATTR
+run_sht21()
+{
+  uint8_t rev;
+  float value;
+  uint8_t sn[8];
+  esp_i2c_err err;
+
+  err = esp_sht21_init(SCL, SDA);
+  if (err != ESP_I2C_OK) {
+    os_printf("SHT21 init error.\n");
+    return;
+  }
+
+  err = esp_sht21_get_sn(sn);
+  if (err != ESP_I2C_OK) os_printf("SHT21 sn error %d.\n", err);
+
+  os_printf("SHT21 SN: %02X:%02X:%02X:%02X:%02X:%02X:%02X:%02X\n",
+            sn[0], sn[1], sn[2], sn[3],
+            sn[4], sn[5], sn[6], sn[7]);
+
+  err = esp_sht21_get_rev(&rev);
+  if (err != ESP_I2C_OK) os_printf("SHT21 sn error %d.\n", err);
+
+  os_printf("Firmware rev: 0x%02X\n", rev);
+
+  err = esp_sht21_get_rh(&value);
+  if (err != ESP_I2C_OK) os_printf("Get RH error: %d\n", err);
+
+  os_printf("Humidity: %s%%\n", esp_util_ftoa(value, 2));
+
+  err = esp_sht21_get_temp_last(&value);
+  if (err != ESP_I2C_OK) os_printf("Get TEMP error: %d\n", err);
+
+  os_printf("Temperature: %s deg. C\n", esp_util_ftoa(value, 2));
+}
+
+void ICACHE_FLASH_ATTR
+user_init()
+{
+  // We don't need WiFi for this example.
+  wifi_station_disconnect();
+  wifi_set_opmode(NULL_MODE);
+
+  stdout_init(BIT_RATE_74880);
+  os_printf("Starting...\n");
+
+  os_timer_disarm(&timer);
+  os_timer_setfn(&timer, (os_timer_func_t *) run_sht21, NULL);
+  os_timer_arm(&timer, 1500, false);
+}