Hi,
I'm using a Raspberry PI 2 B (Raspian 10). I've also tested the Modem at a Ubuntu 20.04 computer (with the same result).
The Raspi has no serial USB interfaces when the modem is not plugged in.
After plugging in the TRM250 modem, I got the linux devices ttyUSB0 and ttyUSB1.
Here is the dmesg output:
[245635.466749] usb 1-1.2.3: new high-speed USB device number 11 using dwc_otg
[245635.599310] usb 1-1.2.3: New USB device found, idVendor=2c7c, idProduct=0296, bcdDevice= 0.00
[245635.599338] usb 1-1.2.3: New USB device strings: Mfr=3, Product=2, SerialNumber=4
[245635.599380] usb 1-1.2.3: Product: Qualcomm CDMA Technologies MSM
[245635.599398] usb 1-1.2.3: Manufacturer: Qualcomm, Incorporated
[245635.599414] usb 1-1.2.3: SerialNumber: 8eb94a57
[245635.602162] option 1-1.2.3:1.0: GSM modem (1-port) converter detected
[245635.602965] usb 1-1.2.3: GSM modem (1-port) converter now attached to ttyUSB0
[245635.604325] option 1-1.2.3:1.1: GSM modem (1-port) converter detected
[245635.605132] usb 1-1.2.3: GSM modem (1-port) converter now attached to ttyUSB1
[245635.617256] qmi_wwan 1-1.2.3:1.4: cdc-wdm0: USB WDM device
[245635.619451] qmi_wwan 1-1.2.3:1.4 wwan0: register 'qmi_wwan' at usb-3f980000.usb-1.2.3, WWAN/QMI device, 06:cd:9d:0e:35:72
Here is the modem part of the /sys/kernel/debug/usr/devices file:
T: Bus=01 Lev=03 Prnt=04 Port=02 Cnt=03 Dev#= 11 Spd=480 MxCh= 0
D: Ver= 2.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS=64 #Cfgs= 1
P: Vendor=2c7c ProdID=0296 Rev= 0.00
S: Manufacturer=Qualcomm, Incorporated
S: Product=Qualcomm CDMA Technologies MSM
S: SerialNumber=8eb94a57
C:* #Ifs= 5 Cfg#= 1 Atr=e0 MxPwr=500mA
I:* If#= 0 Alt= 0 #EPs= 2 Cls=ff(vend.) Sub=ff Prot=ff Driver=option
E: Ad=81(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
E: Ad=01(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms
I:* If#= 1 Alt= 0 #EPs= 2 Cls=ff(vend.) Sub=ff Prot=ff Driver=option
E: Ad=82(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
E: Ad=02(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms
I:* If#= 2 Alt= 0 #EPs= 3 Cls=ff(vend.) Sub=ff Prot=ff Driver=(none)
E: Ad=83(I) Atr=03(Int.) MxPS= 64 Ivl=2ms
E: Ad=84(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
E: Ad=03(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms
I:* If#= 3 Alt= 0 #EPs= 3 Cls=ff(vend.) Sub=fe Prot=ff Driver=(none)
E: Ad=85(I) Atr=03(Int.) MxPS= 64 Ivl=2ms
E: Ad=86(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
E: Ad=04(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms
I:* If#= 4 Alt= 0 #EPs= 3 Cls=ff(vend.) Sub=ff Prot=ff Driver=qmi_wwan
E: Ad=87(I) Atr=03(Int.) MxPS= 64 Ivl=2ms
E: Ad=88(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
E: Ad=05(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms