Using the Sanyo MM-7400 on Linux as a Data Link

I've got a Sanyo MM-7400 with Sprint service. If you've got any of that Sprint Vision Plans (almost impossible not to), that gives you unlimitted used of their 2xRTT service as a mobile modem. 2xRTT equates to about 140 kbs downlink, 50 kbs uplink, with 350 ms ping times. While this is only just usable for an ssh connection (given the ping times), it is fairly usable for things like IM and Web Browsing, as long as you don't mind waiting a little for pages to load.

Required Hardware

You'll need a USB Data cable for this phone. Unfortunately no Sprint stores seem to carry them. Googling around should find you a cable. I've ended up with 2, as the first one I got didn't click into place when linked, so it was always a little precarious to keep the link up.

Kernel Module

Depending on your Linux distro, when you plug in the cable the kernel module may automatically load, and /dev/ttyACM0 will be created. If so, great. If not:

# modprobe cdc-acm

Other documents on the web just refer to this as the ACM module, which took me a while to figure out that cdc-acm was what I needed.

Also note, cdc-acm is not safe to suspend with. Make sure that you drop the ppp connection at least, and better yet, manually unload the cdc-acm module, before suspending. Otherwise you'll get a kernel panic, and so much for your uptime.

PPP Configuration

Once you've installed pppd, you'll need the following config files to make the connection work:

/etc/ppp/peers/sprint:

# You usually need this if there is no PAP authentication
noauth
# The chat script (be sure to edit that file, too!)
connect "/usr/sbin/chat -v -f /etc/ppp/scripts/sprint"
# Set up routing to go through this PPP link
defaultroute
# Use remote DNS
usepeerdns
# Default modem
/dev/ttyACM0
# Connect at high speed
230400
local
novj

/etc/ppp/scripts/sprint:

TIMEOUT         5
ABORT           '\nBUSY\r'
ABORT           '\nERROR\r'
ABORT           '\nNO ANSWER\r'
ABORT           '\nNO CARRIER\r'
ABORT           '\nNO DIALTONE\r'
ABORT           '\nRINGING\r\n\r\nRINGING\r'
''              \rAT
TIMEOUT         12
OK              ATD#777
TIMEOUT         22
CONNECT         ""

Making the Connection

Make the connection with the following command (which can be run as a normal user):

# pppd call sprint 

You should see the word "Data" show up at the front of your phone. If you open it up, it will have RX and TX graphs so that you can see packets comming and going. If it doesn't take the first time, try again after 5 seconds. In some cases the first attempt gets ignored, and I have no idea why.

Dropping the Connection

Also easy:

# killall pppd

Comments on Connectivity

The connection is actually quite awesome. It roams between towers without any drops. I once had a connection up for 3 hours on the highway from NY to MD. Even if you roam out of signal for a few seconds the connection usually holds. If it drops out on you for whatever reason, just drop the connection and restart it later.