How does LoRa socket chose which channel to use when you add several using lora.add_channel ?

[storm 1050]

Hello,

I'm trying to understand on which channel my Lopy4 is sending data, for example if I'm allocating these channel :

Then sending data using :

s = socket.socket(socket.AF_LORA, socket.SOCK_RAW)
s.setsockopt(socket.SOL_LORA, socket.SO_DR, 5)
s.send(packet)

How do I know which channel is used ? I know it's not the last because it's for downlink but for the uplink I've no idea, is there something to configure ? Or is it automatic ?

Thanks

[jcaron]

@storm-1050 Long time since I went into these kind of details, but IIRC all channels you add using add_channel can be used for uplinks. Downlinks are handled separately, according to the region rules and/or configuration sent by the network. You should not add the downlink channel.

The channel listed at index 8 is not a downlink channel, but actually an additional DR on an existing uplink channel.

The device will use any of those links. Don't quite remember if it's round-robin, random, LRU or duty-cycle based, though, but you can check the sources if you want the details. Channel use is also controlled by the network, which can send a mask of which channels to use or not and/or reconfigure channels.

You can know the channel which was used by the last uplink by using lora.stats() (tx_frequency and sftx).

[storm 1050]

Hey thanks for the answer, the lora.stats() is a good tip, as for the source, do you know where is it ? Where am I supposed to search ? Is it the network library ? The socket when you send the packet?
I'm a bit lost on where the algorithm which choose the channel is located.

[jcaron]

@storm-1050 a quick glance makes me think this could be in https://github.com/pycom/pycom-micropython-sigfox/blob/Dev/lib/lora/mac/region/RegionEU868.c starting at line 913, but I really haven’t looked into it in detail.

[storm 1050]

@jcaron It's perfect I found what I want thanks a lot !

So if people want to know, in RegionEU868.c the function RegionEU868NextChannel, call the function CountNbOfEnabledChannels which check all the channel that are enabled ( channel enabled, joined and available for transmission) which get you a list of available channel and then it select one randomly from this list.

In LoRaMac.c in the function ScheduleTx, there is a while loop calling RegionEU868NextChannel till one channel is available