SX1302_HAL/libloragw

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  (C)2020 Semtech

LoRa concentrator HAL user manual

1. Introduction

The LoRa concentrator Hardware Abstraction Layer is a C library that allow you to use a Semtech concentrator chip through a reduced number of high level C functions to configure the hardware, send and receive packets.

The Semtech LoRa concentrator is a digital multi-channel multi-standard packet radio used to send and receive packets wirelessly using LoRa or FSK modulations.

2. Components of the library

The library is composed of the following modules:

1. abstraction layer

• loragw_hal
• loragw_reg
• loragw_aux
• loragw_cal
• loragw_lbt
• loragw_sx1302
• loragw_sx1302_rx
• loragw_sx1302_timestamp
• loragw_sx125x
• loragw_sx1250
• loragw_sx1261

2. communication layer for sx1302

• loragw_com
• loragw_spi
• loragw_usb

3. communication layer for sx1255/SX1257 radios

• sx125x_com
• sx125x_spi

4. communication layer for sx1250 radios

• sx1250_com
• sx1250_spi
• sx1250_usb

5. communication layer for STM32 MCU (USB)

• loragw_mcu

6. communication layer for sx1261 radio (LBT / Spectral Scan)

• sx1261_com
• sx1261_spi
• sx1261_usb

7. peripherals

• loragw_i2c
• loragw_gps
• loragw_stts751
• loragw_ad5338r

The library also contains basic test programs to demonstrate code use and check functionality.

2.1. loragw_hal

This is the main module and contains the high level functions to configure and use the LoRa concentrator:

• lgw_board_setconf, to set the configuration of the concentrator
• lgw_rxrf_setconf, to set the configuration of the radio channels
• lgw_rxif_setconf, to set the configuration of the IF+modem channels
• lgw_txgain_setconf, to set the configuration of the concentrator gain table
• lgw_start, to apply the set configuration to the hardware and start it
• lgw_stop, to stop the hardware
• lgw_receive, to fetch packets if any was received
• lgw_send, to send a single packet (non-blocking, see warning in usage section)
• lgw_status, to check when a packet has effectively been sent
• lgw_get_trigcnt, to get the value of the sx1302 internal counter at last PPS
• lgw_get_instcnt, to get the value of the sx1302 internal counter
• lgw_get_eui, to get the sx1302 chip EUI
• lgw_get_temperature, to get the current temperature
• lgw_time_on_air, to get the Time On Air of a packet
• lgw_spectral_scan_start, to start scaning a particular channel
• lgw_spectral_scan_get_status, to get the status of the current scan
• lgw_spectral_scan_get_results, to get the results of the completed scan
• lgw_spectral_scan_abort, to abort curretn scan

For an standard application, include only this module. The use of this module is detailed on the usage section.

/!\ When sending a packet, there is a delay (approx 1.5ms) for the analog circuitry to start and be stable. This delay is adjusted by the HAL depending on the board version (lgw_i_tx_start_delay_us).

In 'timestamp' mode, this is transparent: the modem is started lgw_i_tx_start_delay_us microseconds before the user-set timestamp value is reached, the preamble of the packet start right when the internal timestamp counter reach target value.

In 'immediate' mode, the packet is emitted as soon as possible: transferring the packet (and its parameters) from the host to the concentrator takes some time, then there is the lgw_i_tx_start_delay_us, then the packet is emitted.

In 'triggered' mode (aka PPS/GPS mode), the packet, typically a beacon, is emitted lgw_i_tx_start_delay_us microsenconds after a rising edge of the trigger signal. Because there is no way to anticipate the triggering event and start the analog circuitry beforehand, that delay must be taken into account in the protocol.

2.2. loragw_reg

This module is used to access to the LoRa concentrator registers by name instead of by address:

• lgw_connect, to initialise and check the connection with the hardware
• lgw_disconnect, to disconnect the hardware
• lgw_reg_r, read a named register
• lgw_reg_w, write a named register
• lgw_reg_rb, read a name register in burst
• lgw_reg_wb, write a named register in burst
• lgw_mem_rb, read from a memory section in burst
• lgw_mem_wb, write to a memory section in burst

This module handles read-only registers protection, multi-byte registers management, signed registers management, read-modify-write routines for sub-byte registers and read/write burst fragmentation to respect SPI/USB maximum burst length constraints.

It make the code much easier to read and to debug. Moreover, if registers are relocated between different hardware revisions but keep the same function, the code written using register names can be reused "as is".

If you need access to all the registers, include this module in your application.

/!\ Warning please be sure to have a good understanding of the LoRa concentrator inner working before accessing the internal registers directly.

2.3. loragw_com

This module contains the functions to access the LoRa concentrator register array through the SPI or USB interfaces:

• lgw_com_r to read one byte
• lgw_com_w to write one byte
• lgw_com_rb to read two bytes or more
• lgw_com_wb to write two bytes or more

This modules is an abstract interface, it then relies on the following modules to actually perform the interfacing:

• loragw_spi : for SPI interface
• loragw_usb : for USB interface

Please do not include that module directly into your application.

/!\ Warning Accessing the LoRa concentrator register array without the checks and safety provided by the functions in loragw_reg is not recommended.

2.4. loragw_aux

This module contains a single host-dependant function wait_ms to pause for a defined amount of milliseconds.

The procedure to start and configure the LoRa concentrator hardware contained in the loragw_hal module requires to wait for several milliseconds at certain steps, typically to allow for supply voltages or clocks to stabilize after been switched on.

An accuracy of 1 ms or less is ideal. If your system does not allow that level of accuracy, make sure that the actual delay is longer that the time specified when the function is called (ie. wait_ms(X) MUST NOT before X milliseconds under any circumstance).

If the minimum delays are not guaranteed during the configuration and start procedure, the hardware might not work at nominal performance. Most likely, it will not work at all.

2.5. loragw_gps

This module contains functions to synchronize the concentrator internal counter with an absolute time reference, in our case a GPS satellite receiver.

The internal concentrator counter is used to timestamp incoming packets and to triggers outgoing packets with a microsecond accuracy. In some cases, it might be useful to be able to transform that internal timestamp (that is independent for each concentrator running in a typical networked system) into an absolute GPS time.

In a typical implementation a GPS specific thread will be called, doing the following things after opening the serial port:

• blocking reads on the serial port (using system read() function)
• parse UBX messages (using lgw_parse_ubx) to get actual native GPS time
• parse NMEA sentences (using lgw_parse_nmea) to get location and UTC time Note: the RMC sentence gives UTC time, not native GPS time.

And each time an NAV-TIMEGPS UBX message has been received:

• get the concentrator timestamp (using lgw_get_trigcnt, mutex needed to protect access to the concentrator)
• get the GPS time contained in the UBX message (using lgw_gps_get)
• call the lgw_gps_sync function (use mutex to protect the time reference that should be a global shared variable).

Then, in other threads, you can simply used that continuously adjusted time reference to convert internal timestamps to GPS time (using lgw_cnt2gps) or the other way around (using lgw_gps2cnt). Inernal concentrator timestamp can also be converted to/from UTC time using lgw_cnt2utc/lgw_utc2cnt functions.

2.6. loragw_sx125x

This module contains functions to handle the configuration of SX1255 and SX1257 radios. In order to communicate with the radio, it relies on the following modules:

• sx125x_com : abstract interfacing to select USB or SPI interface
• sx125x_spi : implementation of the SPI interface

2.7. loragw_sx1250

This module contains functions to handle the configuration of SX1250 radios. In order to communicate with the radio, it relies on the following modules:

• sx1250_com : abstract interfacing to select USB or SPI interface
• sx1250_spi : implementation of the SPI interface
• sx1250_usb : implementation of the USB interface

2.8. loragw_sx1302

This module contains functions to abstract SX1302 concentrator capabilities.

2.9. loragw_sx1302_rx

This module is a sub-module of the loragw_sx1302 module focusing on abstracting the RX buffer of the SX1302.

2.10. loragw_sx1302_timestamp

This module is a sub-module of the loragw_sx1302 module focusing on abstracting the timestamp counter of the SX1302. It converts the 32-bits 32MHz internal counter of the SX1302 to a 32-bits 1MHz counter. This module needs to be called regularly by upper layers to maintain counter wrapping when converting from 32MHz to 1MHz. It also provides function to add correction to the timestamp counter to take into account the LoRa demodulation processing time.

2.11. loragw_stts751

This module contains a very basic driver for the STmicroelectronics ST751 temperature sensor which is on the CoreCell reference design.

2.12. loragw_ad5338r

This module contains a very basic driver for the Analog Devices AD5338R DAC used on the Semtech CN490 Full Duplex reference design to set the PA fixed gain.

2.13. loragw_i2c

This module provides basic function to communicate with I2C devices on the board. It is used in this project for accessing the temperature sensor, the AD5338R DAC...

2.14. loragw_sx1261

This module contains functions to handle the configuration of SX1261 radio for Listen-Before-Talk or Spectral Scan functionnalities. In order to communicate with the radio, it relies on the following modules:

• sx1261_com : abstract interfacing to select USB or SPI interface
• sx1261_spi : implementation of the SPI interface
• sx1261_usb : implementation of the USB interface

This module will also load the sx1261 firmware patch RAM, necessary to support Listen-Before-Talk and spectral scan features, from the sx1261_pram.var file.

2.15. loragw_lbt

This module contains functions to start and stop the Listen-Before-Talk feature when it is enabled. Those functions are called by the lgw_send() function to ensure that the concentrator is allowed to transmit.

Listen-Before-Talk (LBT) and Spectral Scan features need an additional sx1261 radio to be configured.

The Listen-Before-Talk feature works as follows:

• the HAL configures the sx1261 for scanning the channel on which it needs to transmit.
• the SX1261 will scan the channel and set a GPIO to high or low depending if the channel is busy or not (according to scanning parameters)
• the sx1302 AGC firmware will check the status of this GPIO before actually starting the transmit, to ensure it is allowed. The AGC fw sets its status register to inform if the transmit could be done or not.
• the HAL waits for the transmit to be initiated and checks if it was allowed or not.
• the HAL stops the scanning, and return the tramsit status to the caller.

2.16. loragw_mcu

This module contains the functions to setup the communication interface with the STM32 MCU, and to communicate with the sx1302 and the radios when the host and the concentrator are connected through USB llink.

The MCU acts as a simple USB <-> SPI bridge. This means that the HAL running on the host is the same, for both SPI or USB gateways.

But, as the USB communication link brings a 1ms latency for each transfer, the MCU provides a mean to group register write requests in one single USB transfer. It is necessary when a particular configuration has to be done in a time critical task.

For this, 2 new functions has been added:

• lgw_com_set_write_mode, to indicate if the following calls to lgw_com_w(b) need to be grouped on a single USB transfer (BULK mode) or not (SINGLE mode).
• lgw_com_flush, to actually perform the USB transfer of all grouped commands if BULK mode was selected.

Both functions will do nothing in case of SPI.

The same mechanism can be used to configure the sx1261 radio.

3. Software build process

3.1. Details of the software

The library is written following ANSI C conventions but using C99 explicit length data type for all data exchanges with hardware and for parameters.

The loragw_aux module contains POSIX dependant functions for millisecond accuracy pause. For embedded platforms, the function could be rewritten using hardware timers.

3.2. Building options

All modules use a fprintf(stderr,...) function to display debug diagnostic messages if the DEBUG_xxx is set to 1 in library.cfg

3.3. Building procedures

For cross-compilation set the ARCH and CROSS_COMPILE variables in the Makefile, or in your shell environment, with the correct toolchain name and path. ex: export PATH=/home/foo/rpi-toolchain/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin:$PATH export ARCH=arm export CROSS_COMPILE=arm-linux-gnueabihf-

The Makefile in the libloragw directory will parse the library.cfg file and generate a config.h C header file containing #define options. Those options enables and disables sections of code in the loragw_xxx.h files and the *.c source files.

The library.cfg is also used directly to select the proper set of dynamic libraries to be linked with.

3.4. Export

Once build, to use that library on another system, you need to export the following files :

• libloragw/library.cfg -> root configuration file
• libloragw/libloragw.a -> static library, to be linked with a program
• libloragw/readme.md -> required for license compliance
• libloragw/inc/config.h -> C configuration flags, derived from library.cfg
• libloragw/inc/loragw_*.h -> take only the ones you need (eg. _hal and _gps)

After statically linking the library to your application, only the license is required to be kept or copied inside your program documentation.

4. Hardware dependencies

4.1. Hardware revision

The loragw_reg and loragw_hal are written for a specific version on the Semtech hardware (IP and/or silicon revision).

This code has been written for:

• Semtech SX1302 chip
• Semtech SX1250, SX1257 or SX1255 I/Q transceivers

The library will not work if there is a mismatch between the hardware version and the library version. You can use the test program test_loragw_reg to check if the hardware registers match their software declaration.

4.2. GPS receiver (or other GNSS system)

To use the GPS module of the library, the host must be connected to a GPS receiver via a serial link (or an equivalent receiver using a different satellite constellation). The serial link must appear as a "tty" device in the /dev/ directory, and the user launching the program must have the proper system rights to read and write on that device. Use chmod a+rw to allow all users to access that specific tty device, or use sudo to run all your programs (eg. sudo ./test_loragw_gps).

In the current revision, the library only reads data from the serial port, expecting to receive NMEA frames that are generally sent by GPS receivers as soon as they are powered up, and UBX messages which are proprietary to u-blox modules.

The GPS receiver MUST send UBX messages shortly after sending a PPS pulse on to allow internal concentrator timestamps to be converted to absolute GPS time. If the GPS receiver sends a GGA NMEA sentence, the gateway 3D position will also be available.

4.3. Additionnal SX1261 radio

In order to perform Listen-Before-Talk and/or Spectral Scan, an additional SX1261 radio is required. Its internal firmware also needs to be patched (patch RAM) to support those particular features.

5. Usage

5.1. Setting the software environment

For a typical application you need to:

• include loragw_hal.h in your program source
• link to the libloragw.a static library during compilation
• link to the librt library due to loragw_aux dependencies (timing functions)

For an application that will also access the concentrator configuration registers directly (eg. for advanced configuration) you also need to:

• include loragw_reg.h in your program source

5.2. Using the software API

To use the HAL in your application, you must follow some basic rules:

• configure the radios path and IF+modem path before starting the radio
• the configuration is only transferred to hardware when you call the start function
• you cannot receive packets until one (or +) radio is enabled AND one (or +) IF+modem part is enabled AND the concentrator is started
• you cannot send packets until one (or +) radio is enabled AND the concentrator is started
• you must stop the concentrator before changing the configuration

A typical application flow for using the HAL is the following:

<configure the radios and IF+modems>
<start the LoRa concentrator>
loop {
	<fetch packets that were received by the concentrator>
	<process, store and/or forward received packets>
	<send packets through the concentrator>
}
<stop the concentrator>

/!\ Warning The lgw_send function is non-blocking and returns while the LoRa concentrator is still sending the packet, or even before the packet has started to be transmitted if the packet is triggered on a future event. While a packet is emitted, no packet can be received (limitation intrinsic to most radio frequency systems).

Your application must take into account the time it takes to send a packet or check the status (using lgw_status) before attempting to send another packet.

Trying to send a packet while the previous packet has not finished being send will result in the previous packet not being sent or being sent only partially (resulting in a CRC error in the receiver).

5.3. Debugging mode

To debug your application, it might help to compile the loragw_hal function with the debug messages activated (set DEBUG_HAL=1 in library.cfg). It then send a lot of details, including detailed error messages to stderr.

6. Notes

6.1. Spreading factor SF5 & SF6

The sx1302 supports SF5 and SF6 spreading factors, and the HAL also. But it is important to note that the only syncword supported for SF5 and SF6 is 0x12 (also known as "private").

This is true whatever how of the "lorawan_public" field of lgw_conf_board_s is set.

7. License

Copyright (c) 2019, SEMTECH S.A. All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

• Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
• Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
• Neither the name of the Semtech corporation nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL SEMTECH S.A. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

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