This application note explains how to connect to the Internet from the NXP i.MX RT EVK boards running Linux using a USB GSM modem.
The Linux PPP daemon and its shell scripts are used to initiate the connection, receive the networking parameters from the cell (IP, routing, DNS etc) and configure the system networking according to the received parameters. The pppd package integrated by Emcraft into the NXP i.MX RT EVK BSP was obtained from http://www.uclinux.org/pub/uClinux/dist, release 20140504.
The functionality described below is available from the rootfs.uImage project provided by Emcraft for NXP i.MX RT EVK BSP. The generic Linux kernel device driver driver for the USB Modems (CONFIG_USB_ACM) is used in this configuration. Emcraft tested the functionality documented below using the MTD-H5-2.0 HSPA+ USB Cellular Modem from MultiTech Systems.
Cellular Network Configuration
For starting and terminating the PPP connection, the standard scripts from the PPP Daemon package are provided in the rootfs projects. The scripts as follows:
- pon <provider> - starts the PPP daemon with a specified configuraton in /etc/ppp/peers/. Without arguments, the /etc/ppp/peers/provider configuration is used.
- poff - stops the PPP daemon and terminates the connection.
The following PPP configuration files are provided with the rootfs project:
- /etc/ppp/peers/provider - contains the default PPP daemon configuration.
- /etc/ppp/options-mobile - contains the general PPP daemon configuration options (see man pppd). Among others, there are two options enabled for debugging (dump and logfile /dev/console).
- /etc/ppp/chatscripts/mobile-modem.chat - contains modem commands to establish connection with the network.
- /etc/ppp/chatscripts/apn - contains the modem command to configure the Access Point Name specific to the provider.
- /etc/ppp/chatscripts/pin - contains the modem command to configure the SIM-card PIN code, if required. Preconfigured for no PIN in the project.
For a US GSM network operator (AT&T, T-Mobile, Rogers, Bell, Telus, see in http://www.multitech.com/datasheets/86002162.pdf), the current configuration should work, after setting up an appropriate Access Point Name in /etc/ppp/chatscripts/apn and cell account information in /etc/ppp/peers/provider.
For a US CDMA network operator (Verizon, Sprint, Aeris), the modem model Multitech MTD-EV3 should be used. The project provides sample configurations /etc/ppp/peers/verizon and /etc/ppp/chatscripts/verizon.chat, which supposedly should work with Verizon.
To reconfigure the rootfs project for your SIM operator typically you will need:
- Edit the etc/ppp/chatscripts/apn file in projects/rootfs, and change the APN settings appropriately.
- Edit the etc/ppp/peers/provider file in projects/rootfs, and change the account information appropriately.
- Build project/rootfs (Building Linux), and install it to the target (Installing Linux Images to SD Card).
TCP/IP Connectivity Over PPP
Plug-in a USB GSM Modem device to the USB port:
- J9 of NXP i.MX RT1024 EVK;
- USB1 J9 or USB2 J10 of NXP i.MX RT1050 EVK;
- USB1 or USB2 of NXP i.MX RT1170 EVK.
The system will print the appropriate messages to console about the hardware detected:
usb 1-1: not running at top speed; connect to a high speed hub
cdc_acm 1-1:1.0: ttyACM0: USB ACM device
cdc_acm 1-1:1.2: ttyACM1: USB ACM device
cdc_acm 1-1:1.4: ttyACM2: USB ACM device
cdc_acm 1-1:1.6: ttyACM3: USB ACM device
cdc_acm 1-1:1.8: ttyACM4: USB ACM device
cdc_acm 1-1:1.10: ttyACM5: USB ACM device
Shutdown the eth0 network interface:
/ # ifconfig eth0 down
Initiate connection with the cellular network:
/ # pon
/ # pppd options in effect:
debug # (from /etc/ppp/options-mobile)
holdoff 10 # (from /etc/ppp/options-mobile)
persist # (from /etc/ppp/options-mobile)
logfile /dev/console # (from /etc/ppp/options-mobile)
maxfail 0 # (from /etc/ppp/options-mobile)
dump # (from /etc/ppp/options-mobile)
noauth # (from /etc/ppp/options-mobile)
user gdata # (from /etc/ppp/peers/provider)
password ?????? # (from /etc/ppp/peers/provider)
/dev/ttyACM0 # (from /etc/ppp/options-mobile)
115200 # (from /etc/ppp/options-mobile)
lock # (from /etc/ppp/options-mobile)
connect /usr/sbin/chat -v -t15 -f /etc/ppp/chatscripts/mobile-modem.chat
# (from /etc/ppp/peers/provider)
crtscts # (from /etc/ppp/options-mobile)
modem # (from /etc/ppp/options-mobile)
passive # (from /etc/ppp/options-mobile)
hide-password # (from /etc/ppp/options-mobile)
novj # (from /etc/ppp/options-mobile)
noipdefault # (from /etc/ppp/options-mobile)
defaultroute # (from /etc/ppp/options-mobile)
usepeerdns # (from /etc/ppp/options-mobile)
Serial connection established.
using channel 1
Using interface ppp0
Connect: ppp0 <--> /dev/ttyACM0
rcvd [LCP ConfReq id=0x1 <asyncmap 0x0> <auth pap> <magic 0x8a09e49c> <pcomp>
<accomp>]
sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x6b1b2234> <pcomp> <accomp>]
sent [LCP ConfAck id=0x1 <asyncmap 0x0> <auth pap> <magic 0x8a09e49c> <pcomp>
<accomp>]
rcvd [LCP ConfAck id=0x1 <asyncmap 0x0> <magic 0x6b1b2234> <pcomp> <accomp>]
sent [PAP AuthReq id=0x1 user="gdata" password=<hidden>]
rcvd [PAP AuthAck id=0x1 ""]
PAP authentication succeeded
sent
[CCP ConfReq id=0x1 <deflate 15> <deflate(old#) 15> <bsd v1 15>]
sent [IPCP ConfReq id=0x1 <addr 0.0.0.0> <ms-dns1 0.0.0.0> <ms-dns2 0.0.0.0>]
rcvd [LCP ProtRej id=0x2 80 fd 01 01 00 0f 1a 04 78 00 18 04 78 00 15]
Protocol-Reject for 'Compression Control Protocol' (0x80fd) received
sent [IPCP ConfReq id=0x1 <addr 0.0.0.0> <ms-dns1 0.0.0.0>
<ms-dns2 0.0.0.0>]
rcvd [IPCP ConfReq id=0x1]
sent [IPCP ConfNak id=0x1 <addr 0.0.0.0>]
rcvd [IPCP ConfNak id=0x1 <addr 10.146.247.124> <ms-dns1
10.152.222.141> <ms-dns2 10.152.222.132>]
sent [IPCP ConfReq id=0x2 <addr 10.146.247.124> <ms-dns1
10.152.222.141> <ms-dns2 10.152.222.132>]
rcvd [IPCP ConfReq id=0x2 <addr 10.146.247.124>]
sent [IPCP ConfAck id=0x2 <addr 10.146.247.124>]
rcvd [IPCP ConfAck id=0x2 <addr 10.146.247.124> <ms-dns1
10.152.222.141> <ms-dns2 10.152.222.132>]
ioctl(SIOCDELRT): No such process(3)
local IP address 10.146.247.124
remote IP address 10.146.247.124
primary DNS address 10.152.222.141
secondary DNS address 10.152.222.132
Script /etc/ppp/ip-up started (pid 98)
Script /etc/ppp/ip-up finished (pid 98), status = 0x0
Verify that the connection is established (depending on the cellular network, the link may take up to 10 seconds to get established):
/ # ifconfig ppp0
ppp0 Link encap:Point-to-Point Protocol
inet addr:10.146.247.124 P-t-P:10.146.247.124 Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1500 Metric:1
RX packets:4 errors:0 dropped:0 overruns:0 frame:0
TX packets:6 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:3
RX bytes:58 (58.0 B) TX bytes:101 (101.0 B)
Check that the TCP/IP connection to the Internet over PPP has been configured:
/ # netstat -rn
Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface
0.0.0.0 0.0.0.0 0.0.0.0 U 0 0 0 ppp0
10.146.247.124 0.0.0.0 255.255.255.255 UH 0 0 0 ppp0
Ping a remote host to check that network is set up correctly:
/ # ping google.com -c 3
PING google.com (173.194.222.138): 56 data bytes
64 bytes from 173.194.222.138: seq=0 ttl=102 time=509.361 ms
64 bytes from 173.194.222.138: seq=1 ttl=102 time=443.468 ms
64 bytes from 173.194.222.138: seq=2 ttl=102 time=453.504 ms
--- google.com ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max = 443.468/468.777/509.361 ms
Download a file from a remote host:
/ # wget ftp://ftp.gnu.org/README
Connecting to ftp.gnu.org (209.51.188.20:21) README 100% |*******************************| 2748 0:00:00 ETA
Close the TCP/IP connection:
/ # poff
Terminating on signal 15
Connect time 2.3 minutes.
Sent 2229 bytes, received 8071 bytes.
/ # Script /etc/ppp/ip-down started (pid 116)
sent [LCP TermReq id=0x2 "User request"]
rcvd [LCP TermAck id=0x2]
Connection terminated.
Script /etc/ppp/ip-down finished (pid 116), status = 0x0
