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Lora Gateway HAL
================
1. Introduction
---------------
The Lora Gateway Hardware Abstraction Layer is a C library that allow you to use a Semtech Lora gateway hardware through a reduced number of high level C functions to configure the hardware, send and receive packets.
The Semtech Lora gateway is a digital multi-channel multi-standard packet radio used to send and receive packets wirelessly using Lora, FSK or GFSK modulations.
2. Components of the library
----------------------------
The library is composed of 4 modules:
* loragw_hal
* loragw_reg
* loragw_spi
* loragw_aux
The library also contains 3 test program 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 gateway:
* lgw_rxrf_setconf, to set the configuration of the radio channels
* lgw_rxif_setconf, to set the configuration of the IF+modem channels
* 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)
For an standard application, include only this module.
The use of this module is detailed on the usage section.
### 2.2. loragw_reg ###
This module is used to access to the Lora gateway 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_soft_reset, to reset the whole hardware by resetting the register array
* lgw_reg_check, to check all registers vs. their default value and output the result to a file
* 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
This module handles pagination, 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 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 gateway inner working before accessing the internal registers directly.
### 2.3. loragw_spi ###
This module contains the functions to access the Lora gateway register array through the SPI interface:
* lgw_spi_r to read one byte
* lgw_spi_w to write one byte
* lgw_spi_rb to read two bytes or more
* lgw_spi_wb to write two bytes or more
Please *do not* include that module directly into your application.
**/!\ Warning** Accessing the Lora gateway 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 gateway 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 doesn't 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.
3. Software dependencies
------------------------
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 times.
All modules use the fprintf(stderr,...) function to display debug diagnostic messages if the DEBUG flag is defined (eg. for GCC, add the -DDEBUG flag).
4. Hardware dependencies
------------------------
The loragw_reg and loragw_hal are written for a specific version on the Semtech hardware.
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.
loragw_spi contains 4 SPI functions (read, write, burst read, burst write) that are platform-dependant.
The functions must rewritten depending on the SPI bridge you use:
* SPI master matched to the Linux SPI device driver (provided)
* SPI over USB using FTDI components (not provided)
* native SPI using a microcontroller peripheral (not provided)
You can use the test program test_loragw_spi to check with a logic analyser that the SPI communication is working
5. Usage
--------
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 gateway is started
* you cannot send packets until one (or +) radio is enabled AND the gateway is started
* you must stop the gateway before changing the configuration
A typical application flow for using the HAL is the following:
<configure the radios and IF+modems>
<start the Lora gateway>
loop {
<fetch packets that were received by the gateway>
<process, store and/or forward received packets>
<send packets through the gateway>
}
<stop the gateway>
To debug your application, it might help to compile the loragw_hal function with the DEBUG flag defined.
It then send a lot of details, including detailed error messages to *stderr*.
**/!\ Warning** The lgw_send function is non-blocking and returns while the Lora gateway 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.
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).
6. License
----------
To Be Defined.
*EOF*
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