This repository contains the IBM LMIC (LoraMAC-in-C) library, slightly
modified to run in the Arduino environment, allowing using the SX1272,
SX1276 transceivers and compatible modules (such as some HopeRF RFM9x
modules and the Murata LoRa modules).
This library mostly exposes the functions defined by LMIC, it makes no
attempt to wrap them in a higher level API that is more in the Arduino
style. To find out how to use the library itself, see the examples, or
see the PDF file in the doc subdirectory.
The [MCCI arduino-lorawan](https://github.com/mcci-catena/arduino-lorawan) library provides a higher level, more Arduino-like wrapper which may be useful.
This library requires Arduino IDE version 1.6.6 or above, since it
`-D CFG_in866` | `LMIC_REGION_in866` | 9 | 2.9 | India 865-867 MHz ISM
You should define exactly one of `CFG_...` variables. If you don't,
the library assumes `CFG_eu868`. The library changes configuration pretty substantially
according to the region. Some of the differences are listed below.
#### eu868, as923, in866
If the library is configured for EU868, AS923, or IN866 operation, we make
the following changes:
- Add the API `LMIC_setupBand()`.
- Add the constants `MAX_CHANNELS`, `MAX_BANDS`, `LIMIT_CHANNELS`, `BAND_MILLI`,
`BAND_CENTI`, `BAND_DECI`, and `BAND_AUX`.
#### us915, au921
If the library is configured for US915 operation, we make the following changes:
- Add the APIs `LMIC_enableChannel()`,
`LMIC_enableSubBand()`, `LMIC_disableSubBand()`, and `LMIC_selectSubBand()`.
- Add the constants `MAX_XCHANNELS`.
- Add a number of additional `DR_...` symbols.
### Selecting the target radio transceiver
You should define one of the following variables. If you don't, the library assumes
sx1276. There is a runtime check to make sure the actual transceiver matches the library
configuration.
`#define CFG_sx1272_radio 1`
Configures the library for use with an sx1272 transceiver.
`#define CFG_sx1276_radio 1`
Configures the library for use with an sx1276 transceiver.
### Controlling use of interrupts
`#define LMIC_USE_INTERRUPTS`
If defined, configures the library to use interrupts for detecting events from the transceiver. If left undefined, the library will poll for events from the transceiver. See [Timing](#timing) for more info.
### Disabling PING
`#define DISABLE_PING`
If defined, removes all code needed for PING. Removes the APIs `LMIC_setPingable()` and `LMIC_stopPingable()`.
Class A devices don't support PING, so defining `DISABLE_PING` is often a good idea.
By default, PING support is included in the library.
### Disabling Beacons
`#define DISABLE_BEACONS`
If defined, removes all code needed for handling beacons. Removes the APIs `LMIC_enableTracking()` and `LMIC_disableTracking()`.
Class A devices don't support beacons, so defining `DISABLE_BEACONS` might be a good idea.
The remaining variables are rarely used, but we list them here for completeness.
#### Changing debug output
`#define LMIC_PRINTF_TO SerialLikeObject`
This variable should be set to the name of a `Serial`-like object, used for printing messages. If not defined, `Serial`
is assumed.
#### Getting debug from the RF library
`#define LMIC_DEBUG_LEVEL number /* 0, 1, or 2 */`
This variable determines the amount of debug output to be produced by the library. The default is `0`.
If `LMIC_DEBUG_LEVEL` is zero, no output is produced. If `1`, limited output is produced. If `2`, more extensive
output is produced. If non-zero, printf() is used, and the Arduino environment must be configured to support it,
otherwise the sketch will crash at runtime.
#### Selecting the AES library
The library comes with two AES implementations. The original implementation is better on
ARM processors becasue it's faster, but it's larger. For smaller AVR8 processors, a
second library ("IDEETRON") is provided that has a smaller code footprint.
You may define one of the following variables to choose the AES implementation. If you don't,
the library uses the IDEETRON version.
`#define USE_ORIGINAL_AES`
If defined, the original AES implementation is used.
`#define USE_IDEETRON_AES`
If defined, the IDEETRON AES implementation is used.
#### Defining the OS Tick Frequency
`#define US_PER_OSTICK_EXPONENT number`
This variable should be set to the base-2 logarithm of the number of microseconds per OS tick. The default is 4,
which indicates that each tick corresponds to 16 microseconds (because 16 == 2^4).
#### Setting the SPI-bus frequency
`#define LMIC_SPI_FREQ floatNumber`
This variable sets the default frequency for the SPI bus connection to the transceiver. The default is `1E6`, meaning 1 MHz. However, this can be overridden by the contents of the `lmic_pinmap` structure, and we recommend that you use that approach rather than editing the `project_settings/lmic_project_config.h` file.
#### Changing handling of runtime assertion failures
The variables `LMIC_FAILURE_TO` and `DISABLE_LMIC_FAILURE_TO`
control the handling of runtime assertion failures. By default, assertion messages are displayed using
the `Serial` object. You can define LMIC_FAILURE_TO to be the name of some other `Print`-like obect. You can
also define `DISABLE_LMIC_FAILURE_TO` to any value, in which case assert failures will silently halt execution.
#### Disabling JOIN
`#define DISABLE_JOIN`
If defined, removes code needed for OTAA activation. Removes the APIs `LMIC_startJoining()` and `LMIC_tryRejoin()`.
#### Disabling Class A MAC commands
`DISABLE_MCMD_DCAP_REQ`, `DISABLE_MCMD_DN2P_SET`, and `DISABLE_MCMD_SNCH_REQ` respectively disable code for various Class A MAC
commands.
#### Disabling Class B MAC commands
`DISABLE_MCMD_PING_SET` disables the PING_SET MAC commands. It's implied by `DISABLE_PING`.
`DISABLE_MCMD_BCNI_ANS` disables the next-beacon start command. It's implied by `DISABLE_BEACON`
#### Special purpose
`#define DISABLE_INVERT_IQ_ON_RX` disables the inverted Q-I polarity on RX. If this is defined, end-devices will be able
to receive messages from each other, but will not be able to hear the gateway.
## Supported hardware
This library is intended to be used with plain LoRa transceivers,
connecting to them using SPI. In particular, the SX1272 and SX1276
families are supported (which should include SX1273, SX1277, SX1278 and
SX1279 which only differ in the available frequencies, bandwidths and
spreading factors). It has been tested with both SX1272 and SX1276
chips, using the Semtech SX1272 evaluation board and the HopeRF RFM92
and RFM95 boards (which supposedly contain an SX1272 and SX1276 chip
respectively).
This library contains a full LoRaWAN stack and is intended to drive
these Transceivers directly. It is *not* intended to be used with
full-stack devices like the Microchip RN2483 and the Embit LR1272E.
These contain a transceiver and microcontroller that implements the
LoRaWAN stack and exposes a high-level serial interface instead of the
low-level SPI transceiver interface.
This library is intended to be used inside the Arduino environment. It
should be architecture-independent, so it should run on "normal" AVR
arduinos, but also on the ARM-based ones, and some success has been seen
running on the ESP8266 board as well. It was tested on the Arduino Uno,
Pinoccio Scout, Teensy LC and 3.x, ESP8266, Arduino 101, Adafruit Feather M0 LoRa 900. It has been tested on the Lattice RISC-V CPU soft core running in an iCE40 UltraPlus, and also on the Murata LoRaWAN module on the MCCI Catena 4551.
This library an be quite heavy on small systems, especially if the fairly small ATmega
328p (such as in the Arduino Uno) is used. In the default configuration,
the available 32K flash space is nearly filled up (this includes some
debug output overhead, though). By disabling some features in `project_settings/lmic_project_config.h`
(like beacon tracking and ping slots, which are not needed for Class A devices),
some space can be freed up.
## Connections
To make this library work, your Arduino (or whatever Arduino-compatible
board you are using) should be connected to the transceiver. In some cases (such as the Adafruit Feather series and Murata-based boards such as the MCCI Catena 4551), the settings are fixed by the board, and you won't have to worry about many of these details. However, you'll need to find the configuration that's suitable for your board.
> To help you know if you have to worry, we'll call such boards "pre-integrated" and prefix each section with suitable guidance.
The exact
connections are a bit dependent on the transceiver board and Arduino
used, so this section tries to explain what each connection is for and
in what cases it is (not) required.
Note that the SX1272 module runs at 3.3V and likely does not like 5V on
its pins (though the datasheet is not say anything about this, and my
transceiver did not obviously break after accidentally using 5V I/O for
a few hours). To be safe, make sure to use a level shifter, or an
Arduino running at 3.3V. The Semtech evaluation board has 100 ohm resistors in
series with all data lines that might prevent damage, but I would not
count on that.
### Power
> If you're using a pre-integrated board, you can skip this section.
The SX127x transceivers need a supply voltage between 1.8V and 3.9V.
Using a 3.3V supply is typical. Some modules have a single power pin
(like the HopeRF modules, labeled 3.3V) but others expose multiple power
pins for different parts (like the Semtech evaluation board that has
`VDD_RF`, `VDD_ANA` and `VDD_FEM`), which can all be connected together.
Any *GND* pins need to be connected to the Arduino *GND* pin(s).
### SPI
> If you're using a pre-integrated board, you can skip this section, and instead refer to your board's documentation on the pins to be used.
The primary way of communicating with the transceiver is through SPI
(Serial Peripheral Interface). This uses four pins: MOSI, MISO, SCK and
SS. The former three need to be directly connected: so MOSI to MOSI,
MISO to MISO, SCK to SCK. Where these pins are located on your Arduino
varies, see for example the "Connections" section of the [Arduino SPI
documentation](SPI).
The SS (slave select) connection is a bit more flexible. On the SPI
slave side (the transceiver), this must be connect to the pin
(typically) labeled *NSS*. On the SPI master (Arduino) side, this pin
can connect to any I/O pin. Most Arduinos also have a pin labeled "SS",
but this is only relevant when the Arduino works as an SPI slave, which
is not the case here. Whatever pin you pick, you need to tell the
library what pin you used through the pin mapping (see [below](#pin-mapping)).
[SPI]: https://www.arduino.cc/en/Reference/SPI
### DIO pins
> If you're using a pre-integrated board, you can ignore this section; refer to your board's documentation for information on what DIO pins need to be used.
The DIO (digital I/O) pins on the SX127x can be configured
for various functions. The LMIC library uses them to get instant status
information from the transceiver. For example, when a LoRa transmission
starts, the DIO0 pin is configured as a TxDone output. When the
transmission is complete, the DIO0 pin is made high by the transceiver,
which can be detected by the LMIC library.
The LMIC library needs only access to DIO0, DIO1 and DIO2, the other
DIOx pins can be left disconnected. On the Arduino side, they can
connect to any I/O pin. If interrupts are used, the accuracy of timing
will be improved, particularly the rest of your `loop()` function has
lengthy calculations; but in that case, the enabled DIO pins must all
support rising-edge interrupts. See the [Timing](#timing) section below.
In LoRa mode the DIO pins are used as follows:
* DIO0: TxDone and RxDone
* DIO1: RxTimeout
In FSK mode they are used as follows::
* DIO0: PayloadReady and PacketSent
* DIO2: TimeOut
Both modes need only 2 pins, but the transceiver does not allow mapping
them in such a way that all needed interrupts map to the same 2 pins.
So, if both LoRa and FSK modes are used, all three pins must be
connected.
The pins used on the Arduino side should be configured in the pin
mapping in your sketch, by setting the values of `lmic_pinmap::dio[0]`, `[1]`, and `[2]` (see [below](#pin-mapping)).
### Reset
> If you're using a pre-configured module, refer to the documentation for your board.
The transceiver has a reset pin that can be used to explicitly reset
it. The LMIC library uses this to ensure the chip is in a consistent
state at startup. In practice, this pin can be left disconnected, since
the transceiver will already be in a sane state on power-on, but
connecting it might prevent problems in some cases.
On the Arduino side, any I/O pin can be used. The pin number used must
be configured in the pin mapping `lmic_pinmap::rst` field (see [below](#pin-mapping)).
### RXTX
> If you're using a pre-configured module, refer to the documentation for your board.
The transceiver contains two separate antenna connections: One for RX
and one for TX. A typical transceiver board contains an antenna switch
chip, that allows switching a single antenna between these RX and TX
connections. Such a antenna switcher can typically be told what
position it should be through an input pin, often labeled *RXTX*.
The easiest way to control the antenna switch is to use the *RXTX* pin
on the SX127x transceiver. This pin is automatically set high during TX
and low during RX. For example, the HopeRF boards seem to have this
connection in place, so they do not expose any *RXTX* pins and the pin
can be marked as unused in the pin mapping.
Some boards do expose the antenna switcher pin, and sometimes also the
SX127x *RXTX* pin. For example, the SX1272 evaluation board calls the
former *FEM_CTX* and the latter *RXTX*. Again, simply connecting these
together with a jumper wire is the easiest solution.
Alternatively, or if the SX127x *RXTX* pin is not available, LMIC can be
configured to control the antenna switch. Connect the antenna switch
control pin (e.g. *FEM_CTX* on the Semtech evaluation board) to any I/O
pin on the Arduino side, and configure the pin used in the pin map (see
[below](#pin-mapping)).
The configuration entry `lmic_pinmap::rxtx` configures the pin to be used for the *RXTX* control function, in terms of the Arduino `wire.h` digital pin number. If set to `LMIC_UNUSED_PIN`, then the library assumes that software does not need to control the antenna switch.
### RXTX Polarity
If an external switch is used, you also must specify the polarity. Some modules want *RXTX* to be high for transmit, low for receive; Others want it to be low for transmit, high for receive. The Murata module, for example, requires that *RXTX* be *high* for receive, *low* for transmit.
The configuration entry `lmic_pinmap::rxtx_rx_active` should be set to the state to be written to the *RXTX* pin to make the receiver active. The opposite state is written to make the transmitter active. If `lmic_pinmap::rxtx` is `LMIC_UNUSED_PIN`, then the value of `lmic_pinmap::rxtx_rx_active` is ignored.
### Pin mapping
> For pre-configured boards, refer to the documentation on your board for the required settings. See the following:
If you don't have the board documentation, you need to provide your own `lmic_pinmap` values. As described above, a variety of configurations are possible. To tell the LMIC library how your board is configured, you must declare a variable containing a pin mapping struct in the sketch file.
For example, this could look like this:
```c++
lmic_pinmap lmic_pins = {
.nss = 6,
.rxtx = LMIC_UNUSED_PIN,
.rst = 5,
.dio = {2, 3, 4},
// optional: set polarity of rxtx pin.
.rxtx_rx_active = 0,
// optional: set RSSI cal for listen-before-talk
// this value is in dB, and is added to RSSI
// measured prior to decision.
// Must include noise guardband! Ignored in US,
// EU, IN, other markets where LBT is not required.
.rssi_cal = 0,
// optional: override LMIC_SPI_FREQ if non-zero
.spi_freq = 0,
};
```
The names refer to the pins on the transceiver side, the numbers refer
to the Arduino pin numbers (to use the analog pins, use constants like
`A0`). For the DIO pins, the three numbers refer to DIO0, DIO1 and DIO2
respectively. Any pins that are not needed should be specified as
`LMIC_UNUSED_PIN`. The nss and dio0 pin is required, the others can
potentially left out (depending on the environments and requirements,
see the notes above for when a pin can or cannot be left out).
The name of the variable containing this struct must always be `lmic_pins`, which is a special name recognized by the library.
<!-- there are links to the following section, so be careful when renaming -->
#### Adafruit Feather M0 LoRa
See Adafruit's [Feather M0 LoRa product page](https://www.adafruit.com/product/3178).
This board uses the following pin mapping, as shown in the various "...-feather"
sketches.
DIO0 is hard-wired by Adafruit to Arduino D3, but DIO1 is not connected to any Arduino pin (it comes to JP1 pin 1, but is not otherwise connected). This pin table assumes that you have manually wired JP1 pin 1 to Arduino JP3 pin 9 (Arduino D6).
DIO2 is not connected.
```c++
const lmic_pinmap lmic_pins = {
.nss = 8,
.rxtx = LMIC_UNUSED_PIN,
.rst = 4,
.dio = {3, 6, LMIC_UNUSED_PIN},
};
```
<!-- there are links to the following section, so be careful when renaming -->
#### Adafruit Feather 32u4 LoRa
See Adafruit's [Feather 32u4 LoRa product page](https://www.adafruit.com/product/3078). This board is supported by the [ttn-otaa-feather-us915.ino](examples/ttn-otaa-feather-us915/ttn-otaa-feather-us915.ino) example sketch. It uses the same pin mapping as the [Feather M0 LoRa](#adafruit-feather-m0-lora).
<!-- there are links to the following section, so be careful when renaming -->
#### LoRa Nexus by Ideetron
This board uses the following pin mapping:
```c++
const lmic_pinmap lmic_pins = {
.nss = 10,
.rxtx = LMIC_UNUSED_PIN,
.rst = LMIC_UNUSED_PIN, // hardwired to AtMega RESET
.dio = {4, 5, 7},
};
```
<!-- there are links to the following section, so be careful when renaming -->
#### MCCI Catena 4450/4460
See [MCCI Catena 4450](https://store.mcci.com/collections/lorawan-iot-and-the-things-network/products/catena-4450-lorawan-iot-device) and [MCCI Catena 4460](https://store.mcci.com/collections/lorawan-iot-and-the-things-network/products/catena-4460-sensor-wing-w-bme680).
These modules are based on the [Feather M0 LoRa](https://www.adafruit.com/product/3178). Since they include an extra Feather wing for the sensors, the Feather wing includes the trace connecting DIO1 to Arduino D6. No user wiring is needed on the Feather M0.
```c++
const lmic_pinmap lmic_pins = {
.nss = 8,
.rxtx = LMIC_UNUSED_PIN,
.rst = 4,
.dio = {3, 6, LMIC_UNUSED_PIN},
};
```
<!-- there are links to the following section, so be careful when renaming -->
#### MCCI Catena 4551
See [MCCI Catena 4551](https://store.mcci.com/collections/lorawan-iot-and-the-things-network/products/catena-4551-integrated-lorawan-node).
This board uses a Murata LoRa module and has the following pin mapping:
```c++
const lmic_pinmap lmic_pins = {
.nss = 7,
.rxtx = 29,
.rst = 8,
.dio = {25, 26, 27},
// the Murata module needs D29 high for RX, low for TX.
.rxtx_rx_active = 1,
// the Murata module is direct-wired, we can use 8 MHz for SPI.
.spi_freq = 8000000
};
```
## Example Sketches
This library provides several examples.
- [`ttn-otaa.ino`](examples/ttn-otaa/ttn-otaa.ino) shows a basic transmission of a "Hello, world!" message
using the LoRaWAN protocol. It contains some frequency settings and
encryption keys intended for use with The Things Network, but these
also correspond to the default settings of most gateways, so it
should work with other networks and gateways as well.
The example uses over-the-air activation (OTAA) to first join the network to establish a
session and security keys. This was tested with The Things Network,
but should also work (perhaps with some changes) for other networks.
OTAA is the preferred way to work with production LoRaWAN networks.
- [`ttn-otaa-feather-us915.ino`](examples/ttn-otaa-feather-us915/ttn-otaa-feather-us915.ino) is a version of `ttn-otaa.ino` that has
been configured for use with the Feather M0 LoRa, on the US915 bandplan,
with The Things Network. Remember that you may also have to change `config.h`
from defaults. This sketch also works with the MCCI Catena family of products
- [`header_test.ino`](examples/header_test/header_test.ino) just tests the header files; it's used for regression testing.
## Timing
The library is
responsible for keeping track of time of certain network events, and scheduling
other events relative to those events. In particular, the library must note
when a packet finishes transmitting, so it can open up the RX1 and RX2
receive windows at a fixed time after the end of transmission. The library does this
by watching for rising edges on the DIO0 output of the SX127x, and noting the time.
The library observes and processes rising edges on the pins as part of `os_runloop()` processing.
This can be configured in one of two ways (see
[Controlling use of interrupts](#controlling-use-of-interrupts)).
By default, the routine `hal_io_check()`
polls the enabled pins to determine whether an event has occured. This approach
allows use of any CPU pin to sense the DIOs, and makes no assummptions about
interrupts. However, it means that the end-of-transmit event is not observed
(and time-stamped) until `os_runloop()` is called.
Optionally, you can configure the LMIC library to use interrupts. The
interrupt handlers capture the time of
the event. Actual processing is done the next time that `os_runloop()`
is called, using the captured time. However, this requires that the
DIO pins be wired to Arduino pins that support rising-edge interrupts.
Fortunately, LoRa is a fairly slow protocol and the timing of the
receive windows is not super critical. To synchronize transmitter and
receiver, a preamble is first transmitted. Using LoRaWAN, this preamble
consists of 8 symbols, of which the receiver needs to see 4 symbols to
lock on. The current implementation tries to enable the receiver for 5
symbol times at 1.5 symbol after the start of the receive window,
meaning that a inaccuracy of plus or minus 2.5 symbol times should be
acceptable.
The HAL bases all timing on the Arduino `micros()` timer, which has a platform-specific
granularity, and is based on the primary microcontroller clock.
At the fastest LoRa setting supported by the SX127x (SF5BW500) a
single preamble symbol takes 64 microseconds, so the receive window timing should
be accurate within 160 microseconds (for LoRaWAN this is SF7BW250, needing accuracy
within 1280μs). This accuracy should also be
feasible with the polling approach used, provided that the LMIC loop is
run often enough.
If using an internal oscillator (which is 1% - 10%
accurate, depending on calibration), or if your other `loop()` processing
is time consuming, you may have to use [`LMIC_setClockError()`](#lmic_setclockerror)
to cause the library to leave the radio on longer.
An even more accurate solution could be to use a dedicated timer with an
input capture unit, that can store the timestamp of a change on the DIO0
pin (the only one that is timing-critical) entirely in hardware.
Experience shows that this is not normally required, so we leave this as
a customization to be performed on a platform-by-platfom basis. We provide
a special API, `radio_irq_handler_v2(u1_t dio, ostime_t tEvent)`. This
API allows you to supply a hardware-captured time for extra accuracy.
The practical consequence of inaccurate timing is reduced battery life;
the LMIC must turn on the reciever earlier in order to be sure to capture downlink packets.
### `LMIC_setClockError()`
You may call this routine during intialization to infom the LMIC code about the timing accuracy of your system.
```c++
enum { MAX_CLOCK_ERROR = 65535 };
void LMIC_setClockError(
u2_t error
);
```
This function sets the anticipated relative clock error. `MAX_CLOCK_ERROR`
represents +/- 100%, and 0 represents no additional clock compensation.
To allow for an error of 20%, you would call
```c++
LMIC_setClockError(MAX_CLOCK_ERROR * 20 / 100);
```
Setting a high clock error causes the RX windows to be opened earlier than it otherwise would be. This causes more power to be consumed. For Class A devices, this extra power is not substantial, but for Class B devices, this can be significant.
This clock error is not reset by `LMIC_reset()`.
## Downlink datarate
Note that the datarate used for downlink packets in the RX2 window varies by region. Consult your network's manual for any divergences from the LoRaWAN Regional Parameters. This library assumes that the network follows the regional default.
Some networks use different values than the specification. For example, in Europe, the specification default is DR0 (SF12, 125 kHz bandwidth). However, iot.semtech.com and The Things Network both used SF9 / 125 kHz or DR3). If using over-the-air activation (OTAA), the network will download RX2 parameters as part of the JoinAccept message; the LMIC will honor the downloaded parameters.
However, when using personalized activate (ABP), it is your
responsibility to set the right settings, e.g. by adding this to your
sketch (after calling `LMIC_setSession`). `ttn-abp.ino` already does
this.
```c++
LMIC.dn2Dr = DR_SF9;
```
## Encoding Utilities
It is generally important to make LoRaWAN messages as small as practical. Extra bytes mean extra transmit time, which wastes battery power and interferes with other nodes on the network.
To simplify coding, the Arduino header file <lmic.h> defines some data encoding utility functions to encode floating-point data into `uint16_t` values using `sflt16` or `uflt16` bit layout. For even more efficiency, there are versions that use only the bottom 12 bits of the `uint16_t`, allowing for other bits to be carried in the top 4 bits, or for two values to be crammed into three bytes.
-`uint16_t LMIC_f2sflt16(float)` converts a floating point number to a [`sflt16`](#sflt16)-encoded `uint16_t`.
-`uint16_t LMIC_f2uflt16(float)` converts a floating-point number to a [`uflt16`](#uflt16)-encoded `uint16_t`.
-`uint16_t LMIC_f2sflt12(float)` converts a floating-point number to a [`sflt12`](#sflt12)-encoded `uint16_t`, leaving the top four bits of the result set to zero.
-`uint16_t LMIC_f2uflt12(float)` converts a floating-point number to a [`uflt12`](#sflt12)-encoded `uint16_t`, leaving the top four bits of the result set to zero.
JavaScript code for decoding the data can be found in the following sections.
### sflt16
A `sflt16` datum represents an unsigned floating point number in the range [0, 1.0), transmitted as a 16-bit field. The encoded field is interpreted as follows:
bits | description
:---:|:---
15 | Sign bit
14..11 | binary exponent `b`
10..0 | fraction `f`
The corresponding floating point value is computed by computing `f`/2048 * 2^(`b`-15). Note that this format is deliberately not IEEE-compliant; it's intended to be easy to decode by hand and not overwhelmingly sophisticated. However, it is similar to IEEE format in that it uses sign-magnitude rather than twos-complement for negative values.
For example, if the data value is 0x8D, 0x55, the equivalent floating point number is found as follows.
1. The full 16-bit number is 0x8D55.
2. Bit 15 is 1, so this is a negative value.
3.`b` is 1, and `b`-15 is -14. 2^-14 is 1/16384
4.`f` is 0x555. 0x555/2048 = 1365/2048 is 0.667
5.`f * 2^(b-15)` is therefore 0.667/16384 or 0.00004068
6. Since the number is negative, the value is -0.00004068
Floating point mavens will immediately recognize:
* This format uses sign/magnitude representation for negative numbers.
* Numbers do not need to be normalized (although in practice they always are).
* The format is somewhat wasteful, because it explicitly transmits the most-significant bit of the fraction. (Most binary floating-point formats assume that `f` is is normalized, which means by definition that the exponent `b` is adjusted and `f` is shifted left until the most-significant bit of `f` is one. Most formats then choose to delete the most-significant bit from the encoding. If we were to do that, we would insist that the actual value of `f` be in the range 2048..4095, and then transmit only `f - 2048`, saving a bit. However, this complicates the handling of gradual underflow; see next point.)
* Gradual underflow at the bottom of the range is automatic and simple with this encoding; the more sophisticated schemes need extra logic (and extra testing) in order to provide the same feature.
#### JavaScript decoder
```javascript
function sflt162f(rawSflt16)
{
// rawSflt16 is the 2-byte number decoded from wherever;
// it's in range 0..0xFFFF
// bit 15 is the sign bit
// bits 14..11 are the exponent
// bits 10..0 are the the mantissa. Unlike IEEE format,
// the msb is explicit; this means that numbers
// might not be normalized, but makes coding for
// underflow easier.
// As with IEEE format, negative zero is possible, so
// we special-case that in hopes that JavaScript will
// also cooperate.
//
// The result is a number in the open interval (-1.0, 1.0);
//
// throw away high bits for repeatability.
rawSflt16 &= 0xFFFF;
// special case minus zero:
if (rawSflt16 == 0x8000)
return -0.0;
// extract the sign.
var sSign = ((rawSflt16 & 0x8000) != 0) ? -1 : 1;
// extract the exponent
var exp1 = (rawSflt16 >> 11) & 0xF;
// extract the "mantissa" (the fractional part)
var mant1 = (rawSflt16 & 0x7FF) / 2048.0;
// convert back to a floating point number. We hope
// that Math.pow(2, k) is handled efficiently by
// the JS interpreter! If this is time critical code,
// you can replace by a suitable shift and divide.
A `uflt16` datum represents an unsigned floating point number in the range [0, 1.0), transmitted as a 16-bit field. The encoded field is interpreted as follows:
bits | description
:---:|:---
15..12 | binary exponent `b`
11..0 | fraction `f`
The corresponding floating point value is computed by computing `f`/4096 * 2^(`b`-15). Note that this format is deliberately not IEEE-compliant; it's intended to be easy to decode by hand and not overwhelmingly sophisticated.
For example, if the transmitted message contains 0xEB, 0xF7, and the transmitted byte order is big endian, the equivalent floating point number is found as follows.
1. The full 16-bit number is 0xEBF7.
2.`b` is therefore 0xE, and `b`-15 is -1. 2^-1 is 1/2
3.`f` is 0xBF7. 0xBF7/4096 is 3063/4096 == 0.74780...
4.`f * 2^(b-15)` is therefore 0.74780/2 or 0.37390
Floating point mavens will immediately recognize:
* There is no sign bit; all numbers are positive.
* Numbers do not need to be normalized (although in practice they always are).
* The format is somewhat wasteful, because it explicitly transmits the most-significant bit of the fraction. (Most binary floating-point formats assume that `f` is is normalized, which means by definition that the exponent `b` is adjusted and `f` is shifted left until the most-significant bit of `f` is one. Most formats then choose to delete the most-significant bit from the encoding. If we were to do that, we would insist that the actual value of `f` be in the range 4096..8191, and then transmit only `f - 4096`, saving a bit. However, this complicated the handling of gradual underflow; see next point.)
* Gradual underflow at the bottom of the range is automatic and simple with this encoding; the more sophisticated schemes need extra logic (and extra testing) in order to provide the same feature.
#### JavaScript decoder
```javascript
function uflt162f(rawUflt16)
{
// rawUflt16 is the 2-byte number decoded from wherever;
// it's in range 0..0xFFFF
// bits 15..12 are the exponent
// bits 11..0 are the the mantissa. Unlike IEEE format,
// the msb is explicit; this means that numbers
// might not be normalized, but makes coding for
// underflow easier.
// As with IEEE format, negative zero is possible, so
// we special-case that in hopes that JavaScript will
// also cooperate.
//
// The result is a number in the half-open interval [0, 1.0);
//
// throw away high bits for repeatability.
rawUflt16 &= 0xFFFF;
// extract the exponent
var exp1 = (rawUflt16 >> 12) & 0xF;
// extract the "mantissa" (the fractional part)
var mant1 = (rawUflt16 & 0xFFF) / 4096.0;
// convert back to a floating point number. We hope
// that Math.pow(2, k) is handled efficiently by
// the JS interpreter! If this is time critical code,
// you can replace by a suitable shift and divide.
var f_unscaled = mant1 * Math.pow(2, exp1 - 15);
return f_unscaled;
}
```
### sflt12
A `sflt12` datum represents an signed floating point number in the range [0, 1.0), transmitted as a 12-bit field. The encoded field is interpreted as follows:
bits | description
:---:|:---
11 | sign bit
11..8 | binary exponent `b`
7..0 | fraction `f`
The corresponding floating point value is computed by computing `f`/128 * 2^(`b`-15). Note that this format is deliberately not IEEE-compliant; it's intended to be easy to decode by hand and not overwhelmingly sophisticated.
For example, if the transmitted message contains 0x8, 0xD5, the equivalent floating point number is found as follows.
1. The full 16-bit number is 0x8D5.
2. The number is negative.
3.`b` is 0x1, and `b`-15 is -14. 2^-14 is 1/16384
4.`f` is 0x55. 0x55/128 is 85/128, or 0.66
5.`f * 2^(b-15)` is therefore 0.66/16384 or 0.000041 (to two significant digits)
6. The decoded number is therefore -0.000041.
Floating point mavens will immediately recognize:
* This format uses sign/magnitude representation for negative numbers.
* Numbers do not need to be normalized (although in practice they always are).
* The format is somewhat wasteful, because it explicitly transmits the most-significant bit of the fraction. (Most binary floating-point formats assume that `f` is is normalized, which means by definition that the exponent `b` is adjusted and `f` is shifted left until the most-significant bit of `f` is one. Most formats then choose to delete the most-significant bit from the encoding. If we were to do that, we would insist that the actual value of `f` be in the range 128 .. 256, and then transmit only `f - 128`, saving a bit. However, this complicates the handling of gradual underflow; see next point.)
* Gradual underflow at the bottom of the range is automatic and simple with this encoding; the more sophisticated schemes need extra logic (and extra testing) in order to provide the same feature.
* It can be strongly argued that dropping the sign bit would be worth the effort, as this would get us 14% more resolution for a minor amount of work.
#### JavaScript decoder
```javascript
function sflt122f(rawSflt12)
{
// rawSflt12 is the 2-byte number decoded from wherever;
// it's in range 0..0xFFF (12 bits). For safety, we mask
// on entry and discard the high-order bits.
// bit 11 is the sign bit
// bits 10..7 are the exponent
// bits 6..0 are the the mantissa. Unlike IEEE format,
// the msb is explicit; this means that numbers
// might not be normalized, but makes coding for
// underflow easier.
// As with IEEE format, negative zero is possible, so
// we special-case that in hopes that JavaScript will
// also cooperate.
//
// The result is a number in the open interval (-1.0, 1.0);
//
// throw away high bits for repeatability.
rawSflt12 &= 0xFFF;
// special case minus zero:
if (rawSflt12 == 0x800)
return -0.0;
// extract the sign.
var sSign = ((rawSflt12 & 0x800) != 0) ? -1 : 1;
// extract the exponent
var exp1 = (rawSflt12 >> 7) & 0xF;
// extract the "mantissa" (the fractional part)
var mant1 = (rawSflt12 & 0x7F) / 128.0;
// convert back to a floating point number. We hope
// that Math.pow(2, k) is handled efficiently by
// the JS interpreter! If this is time critical code,
// you can replace by a suitable shift and divide.
A `uflt12` datum represents an unsigned floating point number in the range [0, 1.0), transmitted as a 16-bit field. The encoded field is interpreted as follows:
bits | description
:---:|:---
11..8 | binary exponent `b`
7..0 | fraction `f`
The corresponding floating point value is computed by computing `f`/256 * 2^(`b`-15). Note that this format is deliberately not IEEE-compliant; it's intended to be easy to decode by hand and not overwhelmingly sophisticated.
For example, if the transmitted message contains 0x1, 0xAB, the equivalent floating point number is found as follows.
1. The full 16-bit number is 0x1AB.
2.`b` is therefore 0x1, and `b`-15 is -14. 2^-14 is 1/16384
3.`f` is 0xAB. 0xAB/256 is 0.67
4.`f * 2^(b-15)` is therefore 0.67/16384 or 0.0000408 (to three significant digits)
Floating point mavens will immediately recognize:
* There is no sign bit; all numbers are positive.
* Numbers do not need to be normalized (although in practice they always are).
* The format is somewhat wasteful, because it explicitly transmits the most-significant bit of the fraction. (Most binary floating-point formats assume that `f` is is normalized, which means by definition that the exponent `b` is adjusted and `f` is shifted left until the most-significant bit of `f` is one. Most formats then choose to delete the most-significant bit from the encoding. If we were to do that, we would insist that the actual value of `f` be in the range 256 .. 512, and then transmit only `f - 256`, saving a bit. However, this complicates the handling of gradual underflow; see next point.)
* Gradual underflow at the bottom of the range is automatic and simple with this encoding; the more sophisticated schemes need extra logic (and extra testing) in order to provide the same feature.
#### JavaScript decoder
```javascript
function uflt122f(rawUflt12)
{
// rawUflt12 is the 2-byte number decoded from wherever;
// it's in range 0..0xFFF (12 bits). For safety, we mask
// on entry and discard the high-order bits.
// bits 11..8 are the exponent
// bits 7..0 are the the mantissa. Unlike IEEE format,
// the msb is explicit; this means that numbers
// might not be normalized, but makes coding for
// underflow easier.
// As with IEEE format, negative zero is possible, so
// we special-case that in hopes that JavaScript will
// also cooperate.
//
// The result is a number in the half-open interval [0, 1.0);
//
// throw away high bits for repeatability.
rawUflt12 &= 0xFFF;
// extract the exponent
var exp1 = (rawUflt12 >> 8) & 0xF;
// extract the "mantissa" (the fractional part)
var mant1 = (rawUflt12 & 0xFF) / 256.0;
// convert back to a floating point number. We hope
// that Math.pow(2, k) is handled efficiently by
// the JS interpreter! If this is time critical code,
// you can replace by a suitable shift and divide.
- Interim bug fixes: added a new API (`radio_irq_handler_v2()`), which allows the caller to provide the timestamp of the interrupt. This allows for more accurate timing, because the knowledge of interrupt overhead can be moved to a platform-specific layer ([#148](https://github.com/mcci-catena/arduino-lmic/issues/148)). Fixed compile issues on ESP32 ([#140](https://github.com/mcci-catena/arduino-lmic/issues/140) and [#153](https://github.com/mcci-catena/arduino-lmic/issues/150)). We added ESP32 and 32u4 as targets in CI testing. We switched CI testing to Arduino IDE 1.8.7.
Fixed issue [#161](https://github.com/mcci-catena/arduino-lmic/issues/161) selecting the Japan version of as923 using `CFG_as923jp` (selecting via `CFG_as923` and `LMIC_COUNTRY_CODE=LMIC_COUNTRY_CODE_JP` worked).
Fixed [#38](https://github.com/mcci-catena/arduino-lmic/issues/38) -- now any call to hal_init() will put the NSS line in the idle (high/inactive) state. As a side effect, RXTX is initialized, and RESET code changed to set value before transitioning state. Likely no net effect, but certainly more correct.
- V2.2.2 adds `ttn-abp-feather-us915-dht22.ino` example, and fixes some documentation typos. It also fixes encoding of the `Margin` field of the `DevStatusAns` MAC message ([#130](https://github.com/mcci-catena/arduino-lmic/issues/130)). This makes Arduino LMIC work with newtorks implemented with [LoraServer](https://www.loraserver.io/).
- V2.2.1 corrects the value of `ARDUINO_LMIC_VERSION` ([#123](https://github.com/mcci-catena/arduino-lmic/issues/123)), allows ttn-otaa-feather-us915 example to compile for the Feather 32u4 LoRa ([#116](https://github.com/mcci-catena/arduino-lmic/issues/116)), and addresses documentation issues ([#122](https://github.com/mcci-catena/arduino-lmic/issues/122), [#120](https://github.com/mcci-catena/arduino-lmic/issues/120)).
- V2.2.0 adds encoding functions and `tn-otaa-feather-us915-dht22.ino` example. Plus a large number of issues: [#59](https://github.com/mcci-catena/arduino-lmic/issues/59), [#60](https://github.com/mcci-catena/arduino-lmic/issues/60), [#63](https://github.com/mcci-catena/arduino-lmic/issues/63), [#64](https://github.com/mcci-catena/arduino-lmic/issues/47) (listen-before-talk for Japan), [#65](https://github.com/mcci-catena/arduino-lmic/issues/65), [#68](https://github.com/mcci-catena/arduino-lmic/issues/68), [#75](https://github.com/mcci-catena/arduino-lmic/issues/75), [#78](https://github.com/mcci-catena/arduino-lmic/issues/78), [#80](https://github.com/mcci-catena/arduino-lmic/issues/80), [#91](https://github.com/mcci-catena/arduino-lmic/issues/91), [#98](https://github.com/mcci-catena/arduino-lmic/issues/98), [#101](https://github.com/mcci-catena/arduino-lmic/issues/101). Added full Travis CI testing, switched to travis-ci.com as the CI service. Prepared to publish library in the offical Arduino library list.
- V2.1.5 fixes issue [#56](https://github.com/mcci-catena/arduino-lmic/issues/56) (a documentation bug). Documentation was quickly reviewed and other issues were corrected. The OTAA examples were also updated slightly.
- V2.1.4 fixes issues [#47](https://github.com/mcci-catena/arduino-lmic/issues/47) and [#50](https://github.com/mcci-catena/arduino-lmic/issues/50) in the radio driver for the SX1276 (both related to handling of output power control bits).
- V2.1.3 has a fix for issue [#43](https://github.com/mcci-catena/arduino-lmic/issues/43): handling of `LinkAdrRequest` was incorrect for US915 and AU921; when TTN added ADR support on US and AU, the deficiency was revealed (and caused an ASSERT).
- V2.1.2 has a fix for issue [#39](https://github.com/mcci-catena/arduino-lmic/issues/39) (adding a prototype for `LMIC_DEBUG_PRINTF` if needed). Fully upward compatible, so just a patch.
- V2.1.1 has the same content as V2.1.2, but was accidentally released without updating `library.properties`.
- V2.1.0 adds support for the Murata LoRaWAN module.
- V2.0.2 adds support for the extended bandplans.
## Contributions
This library started from the IBM V1.5 open-source code.
- Thomas Telkamp and Matthijs Kooijman ported V1.5 to Arduino and did a lot of bug fixing.
- Terry Moore, LeRoy Leslie, Frank Rose, and ChaeHee Won did a lot of work on US support.
- Terry Moore added the AU921, AS923 and IN866 bandplans, and created the regionalization framework.
- [@tanupoo](https://github.com/tanupoo) of the WIDE Project debugged AS923JP and LBT support.
## Trademark Acknowledgements
LoRa is a registered trademark of the LoRa Alliance. LoRaWAN is a trademark of the LoRa Alliance.
MCCI and MCCI Catena are registered trademarks of MCCI Corporation.
All other trademarks are the properties of their respective owners.
## License
The upstream files from IBM v1.6 are based on the Berkeley license,
and the merge which synchronized this repository therefore migrated
the core files to the Berkeley license. However, modifications made
in the Arduino branch were done under the Eclipse license, so the
overall license of this repository is still Eclipse Public License
v1.0. The examples which use a more liberal
license. Some of the AES code is available under the LGPL. Refer to each
individual source file for more details, but bear in mind that until
the upstream developers look into this issue, it is safest to assume
