Add i2c based module for am2320 humidity sensor

Example use:
> sda=1
> scl=2
> am2320.init(sda,scl)
> rh, t = am2320.read()
> print(string.format("Temperature: %s degrees C", t / 10))
> print(string.format("RH: %s %%", rh / 10))

signed-off-by: henk.vergonet@gmail.com

app/include/user_modules.h

@@ -14,6 +14,7 @@
 #ifndef LUA_CROSS_COMPILER
 
 #define LUA_USE_MODULES_ADC
+//#define LUA_USE_MODULES_AM2320
 //#define LUA_USE_MODULES_APA102
 #define LUA_USE_MODULES_BIT
 //#define LUA_USE_MODULES_BMP085

app/modules/am2320.c

@@ -0,0 +1,153 @@
+/*
+ * app/modules/am2320.c
+ *
+ * Copyright (c) 2016 Henk Vergonet <Henk.Vergonet@gmail.com>
+ *
+ * This program 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 2 of
+ * the License, or (at your option) any later version.
+ *
+ * This program 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, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+#include "module.h"
+#include "lauxlib.h"
+#include "platform.h"
+#include "lwip/udp.h"
+#include <errno.h>
+
+static const uint32_t am2320_i2c_id = 0;
+static const uint8_t am2320_i2c_addr = 0xb8 >> 1;
+
+static uint16_t crc16(uint8_t *ptr, unsigned int len)
+{
+    uint16_t	crc =0xFFFF;
+    uint8_t	i;
+
+    while(len--) {
+	crc ^= *ptr++;
+	for(i=0;i<8;i++) {
+	    if(crc & 0x01) {
+		crc >>= 1;
+		crc ^= 0xA001;
+	    } else {
+		crc >>= 1;
+	    }
+	}
+    }
+    return crc;
+}
+
+/* make sure buf has lenght len+2 in order to accommodate for extra bytes */
+static int _read(uint32_t id, void *buf, uint8_t len, uint8_t off)
+{
+    int i;
+    uint8_t *b = (uint8_t *)buf;
+    uint16_t crc;
+
+    // step 1: Wake sensor
+    platform_i2c_send_start(id);
+    platform_i2c_send_address(id, am2320_i2c_addr, PLATFORM_I2C_DIRECTION_TRANSMITTER);
+    os_delay_us(800);
+    platform_i2c_send_stop(id);
+
+    // step 2: Send read command
+    platform_i2c_send_start(id);
+    platform_i2c_send_address(id, am2320_i2c_addr, PLATFORM_I2C_DIRECTION_TRANSMITTER);
+    platform_i2c_send_byte(id, 0x03);
+    platform_i2c_send_byte(id, off);
+    platform_i2c_send_byte(id, len);
+    platform_i2c_send_stop(id);
+
+    // step 3: Read the data
+    os_delay_us(1500);
+    platform_i2c_send_start(id);
+    platform_i2c_send_address(id, am2320_i2c_addr, PLATFORM_I2C_DIRECTION_RECEIVER);
+    os_delay_us(30);
+    for(i=0; i<len+2; i++)
+	b[i] = platform_i2c_recv_byte(id,1);
+    crc  = platform_i2c_recv_byte(id,1);
+    crc |= platform_i2c_recv_byte(id,0) << 8;
+    platform_i2c_send_stop(id);
+
+    if(b[0] != 0x3 || b[1] != len)
+	return -EIO;
+    if(crc != crc16(b,len+2))
+	return -EIO;
+    return 0;
+}
+
+static int am2320_init(lua_State* L)
+{
+    uint32_t sda;
+    uint32_t scl;
+    int ret;
+    struct {
+    	uint8_t  cmd;
+    	uint8_t  len;
+	uint16_t model;
+	uint8_t	 version;
+	uint32_t id;
+    } nfo;
+
+    if (!lua_isnumber(L, 1) || !lua_isnumber(L, 2)) {
+        return luaL_error(L, "wrong arg range");
+    }
+
+    sda = luaL_checkinteger(L, 1);
+    scl = luaL_checkinteger(L, 2);
+
+    if (scl == 0 || sda == 0) {
+        return luaL_error(L, "no i2c for D0");
+    }
+
+    platform_i2c_setup(am2320_i2c_id, sda, scl, PLATFORM_I2C_SPEED_SLOW);
+
+    os_delay_us(1500); // give some time to settle things down
+    ret = _read(am2320_i2c_id, &nfo, sizeof(nfo)-2, 0x08);
+    if(ret)
+        return luaL_error(L, "transmission error");
+
+    lua_pushinteger(L, ntohs(nfo.model));
+    lua_pushinteger(L, nfo.version);
+    lua_pushinteger(L, ntohl(nfo.id));
+    return 3;
+}
+
+static int am2320_read(lua_State* L)
+{
+    int ret;
+    struct {
+    	uint8_t  cmd;
+    	uint8_t  len;
+	uint16_t rh;
+	uint16_t temp;
+    } nfo;
+ 
+    ret = _read(am2320_i2c_id, &nfo, sizeof(nfo)-2, 0x00);
+    if(ret)
+        return luaL_error(L, "transmission error");
+
+    ret = ntohs(nfo.temp);
+    if(ret & 0x8000)
+    	ret = -(ret & 0x7fff);
+
+    lua_pushinteger(L, ntohs(nfo.rh));
+    lua_pushinteger(L, ret);
+    return 2;
+}
+
+static const LUA_REG_TYPE am2320_map[] = {
+    { LSTRKEY( "read" ), LFUNCVAL( am2320_read )},
+    { LSTRKEY( "init" ), LFUNCVAL( am2320_init )},
+    { LNILKEY, LNILVAL}
+};
+
+NODEMCU_MODULE(AM2320, "am2320", am2320_map, NULL);

docs/en/modules/am2320.md

@@ -0,0 +1,38 @@
+# AM2320 Module
+
+This module provides access to the [AM2320](https://akizukidenshi.com/download/ds/aosong/AM2320.pdf) humidity and temperature sensor, using the i2c interface.
+
+## am2320.init()
+Initializes the module and sets the pin configuration. Returns model, version, serial but is seams these where all zero on my model.
+
+#### Syntax
+`model, version, serial = am2320.init(sda, scl)`
+
+#### Parameters
+- `sda` data pin
+- `scl` clock pin
+
+#### Returns
+- `model`  16 bits number of model
+- `version`  8 bits version number
+- `serial`  32 bits serial number
+
+   Note: I have only observerd values of 0 for all of these, maybe other sensors return more sensible readings.
+
+## am2320.read()
+Samples the sensor and returns the relative humidity in % and temperature in celsius, as an integer multiplied with 10.
+
+#### Syntax
+`am2320.read()`
+
+#### Returns
+- `relative humidity` percentage multiplied with 10 (integer)
+- `temperature` in celcius multiplied with 10 (integer)
+
+#### Example
+```lua
+am2320.init(1, 2)
+rh, t = am2320.read()
+print(string.format("RH: %s%%", rh / 10))
+print(string.format("Temperature: %s degrees C", t / 10))
+

mkdocs.yml

@@ -31,6 +31,7 @@ pages:
     - Support: 'en/support.md'
     - Modules:
         - 'adc': 'en/modules/adc.md'
+        - 'am2320': 'en/modules/am2320.md'
         - 'apa102': 'en/modules/apa102.md'
         - 'bit': 'en/modules/bit.md'
         - 'bmp085': 'en/modules/bmp085.md'