Can LMIC 1.6 be set up to use a single channel and SF?

[arjanvanb (Arjan)]

For the US, which uses 64 channels while gateways might only use 8 (or one, for a single-channel gateway), the following from April 2016 might be relevant:

@cswiger

Huh, turns out the lmic.cpp LMIC_disableChannel(u1_t channel) for CFG_us915 I got from LoRa-Thing/libraries/lmic-v1.5 at master · things4u/LoRa-Thing · GitHub is broken - for

struct lmic_t {
#elif defined(CFG_us915)
    u2_t channelMap[(72+MAX_XCHANNELS+15)/16];  // enabled bits

that should be an array of 5 16 bit values (80 bits, to cover 74 total channels), which when initialized is:

LMIC.channelMap[0] = 0xFFFF    16
LMIC.channelMap[1] = 0xFFFF    32
LMIC.channelMap[2] = 0xFFFF    48
LMIC.channelMap[3] = 0xFFFF    64
LMIC.channelMap[4] = 0x00FF    72 bits

However, LMIC_disableChannel() for CFG_us915 is modulo 4???

LMIC.channelMap[channel/4] &= ~(1<<(channel&0xF));

should be 16. As it is, when you disable channel 4, you actually get 20!

4:    channelMap[0]: ffff  
      channelMap[1]: ffef      1110 1111    wtf??

LMIC_disableChannel(8) turns off the bit for 40, etc. Changed it to:

LMIC.channelMap[channel/16] &= ~(1<<(channel&0xF));

And:

@cswiger

https://github.com/matthijskooijman/arduino-lmic/blob/master/src/lmic/lmic.c

has the same bug:

void LMIC_disableChannel (u1_t channel) {
    if( channel < 72+MAX_XCHANNELS )
        LMIC.channelMap[channel/4] &= ~(1<<(channel&0xF));      
    }

That 4 should be a 16 to get the right byte of the array - only affects CFG_us915

I’ve not validated, but someone might want to create a pull request if this bug is currently still in the code