Quectel BG96: band selection does not take effect

[Reinhard Speyerer]

On Tue, Jul 07, 2020 at 01:56:34PM +0200, Fredrik Flornes Ellertsen wrote:
> Hi,
> 
> We are having trouble with band selection on the Quectel BG96. It seems the
> band selection command executes successfully, but the modem always stays on
> LTE band 20 regardless of the band selection preference. We are using
> ModemManager version 1.10.0 patched with commit f2c878e7 to allow setting
> the band preference without SIGSEGV.
> 
> Here we try to configure the modem to avoid band 20.
> 
> $ mmcli -m 0 --set-current-bands='eutran-8'
> successfully set current bands in the modem
> 
> [...]
> 
> Relevant part of the ModemManager log:
> 
> [...]
> <<<<<<   message     = "Get System Selection Preference" (0x0034)
> ModemManager[6395]: [/dev/cdc-wdm0] received message...
> <<<<<< RAW:
> <<<<<<   length = 151
> <<<<<<   data   =
> 01:96:00:80:03:01:02:4B:00:34:00:8A:00:02:04:00:00:00:00:00:10:01:00:00:11:02:00:10:00:12:08:00:00:00:00:00:00:00:00:00:15:08:00:80:00:00:00:00:00:00:00:16:01:00:00:18:04:00:02:00:00:00:19:04:00:01:00:00:00:1C:05:00:04:08:00:00:04:1D:04:00:00:00:00:00:1F:04:00:02:00:00:00:20:04:00:01:00:00:00:24:08:00:02:00:00:00:00:00:00:00:25:08:00:9F:18:0E:0A:40:00:00:00:26:08:00:9F:18:0E:0A:00:00:00:00:27:11:00:04:08:00:00:00:0A:00:00:00:0B:00:00:00:04:00:00:00
> ModemManager[6395]: [/dev/cdc-wdm0] received generic response
> (translated)...
> <<<<<< QMUX:
> <<<<<<   length  = 150
> <<<<<<   flags   = 0x80
> <<<<<<   service = "nas"
> <<<<<<   client  = 1
> <<<<<< QMI:
> <<<<<<   flags       = "response"
> <<<<<<   transaction = 75
> <<<<<<   tlv_length  = 138
> <<<<<<   message     = "Get System Selection Preference" (0x0034)
> <<<<<< TLV:
> <<<<<<   type       = "Result" (0x02)
> <<<<<<   length     = 4
> <<<<<<   value      = 00:00:00:00
> <<<<<<   translated = SUCCESS
> <<<<<< TLV:
> <<<<<<   type       = "Emergency mode" (0x10)
> <<<<<<   length     = 1
> <<<<<<   value      = 00
> <<<<<<   translated = no
> <<<<<< TLV:
> <<<<<<   type       = "Mode Preference" (0x11)
> <<<<<<   length     = 2
> <<<<<<   value      = 10:00
> <<<<<<   translated = lte
> <<<<<< TLV:
> <<<<<<   type       = "Band Preference" (0x12)
> <<<<<<   length     = 8
> <<<<<<   value      = 00:00:00:00:00:00:00:00
> <<<<<<   translated = (null)
> <<<<<< TLV:
> <<<<<<   type       = "LTE Band Preference" (0x15)
> <<<<<<   length     = 8
> <<<<<<   value      = 80:00:00:00:00:00:00:00
> <<<<<<   translated = 8
> <<<<<< TLV:
> <<<<<<   type       = "Network Selection Preference" (0x16)
> <<<<<<   length     = 1
> <<<<<<   value      = 00
> <<<<<<   translated = automatic
> <<<<<< TLV:
> <<<<<<   type       = "Service Domain Preference" (0x18)
> <<<<<<   length     = 4
> <<<<<<   value      = 02:00:00:00
> <<<<<<   translated = cs-ps
> <<<<<< TLV:
> <<<<<<   type       = "GSM WCDMA Acquisition Order Preference" (0x19)
> <<<<<<   length     = 4
> <<<<<<   value      = 01:00:00:00
> <<<<<<   translated = gsm
> <<<<<< TLV:
> <<<<<<   type       = "Acquisition Order Preference" (0x1c)
> <<<<<<   length     = 5
> <<<<<<   value      = 04:08:00:00:04
> <<<<<<   translated = { [0] = 'lte ' [1] = 'none ' [2] = 'none ' [3] = 'gsm
> '}
> <<<<<< TLV:
> <<<<<<   type   = 0x1d
> <<<<<<   length = 4
> <<<<<<   value  = 00:00:00:00
> <<<<<< TLV:
> <<<<<<   type   = 0x1f
> <<<<<<   length = 4
> <<<<<<   value  = 02:00:00:00
> <<<<<< TLV:
> <<<<<<   type   = 0x20
> <<<<<<   length = 4
> <<<<<<   value  = 01:00:00:00
> <<<<<< TLV:
> <<<<<<   type   = 0x24
> <<<<<<   length = 8
> <<<<<<   value  = 02:00:00:00:00:00:00:00
> <<<<<< TLV:
> <<<<<<   type   = 0x25
> <<<<<<   length = 8
> <<<<<<   value  = 9F:18:0E:0A:40:00:00:00
> <<<<<< TLV:
> <<<<<<   type   = 0x26
> <<<<<<   length = 8
> <<<<<<   value  = 9F:18:0E:0A:00:00:00:00
> <<<<<< TLV:
> <<<<<<   type   = 0x27
> <<<<<<   length = 17
> <<<<<<   value  = 04:08:00:00:00:0A:00:00:00:0B:00:00:00:04:00:00:00
> 
> Resetting the modem doesn't help either. I am not sure whether this mailing
> list is the correct forum for this question or if I should ask Quectel
> about this. Any help is very much appreciated.
> 

Hi Fredrik,

when looking at TLVs 0x24 and 0x25 one can see that their values when
interpreted as a LTE bandmask seem to match the values supported by the
BG96 for Cat-M1 and CAT-NB1.

My guess is that there would also be two additional extended LTE band
preference TLVs for MDM9205-based devices like Quectel BG95 and
Telit ME910G1 since they may support LTE bands > 64:

Regards,
Reinhard