RE: Sierra Wireless (MC8780) HSDPA speed issue

[Ralf Nyren]

Hi,

Three devices appear, ttyUSB0, ttyUSB1, ttyUSB2.

Response from ATI command is as follows:

ttyUSB0:  (this is the device providing high speed connection)
Sierra Wireless, Inc. 
MC8780 
APP1

ttyUSB1: no response here, I understand this device is for the proprietary
protocol...

ttyUSB2:  (this is the device with the speed "problem")
Manufacturer: Sierra Wireless, Inc.
Model: MC8780
Revision: F1_0_0_10AP C:/WS/FW/F1_0_0_10AP/MSM7200R3/SRC/AMSS 2007/11/08 10:51:15
IMEI: 354219010190864
IMEI SV: 7
FSN: D332567166610
3GPP Release 6
+GCAP: +CGSM,+DS,+ES

> From my experience there are very few commands which gives any output at all on
ttyUSB0.  AT+CSQ and AT+COPS? gives output on ttyUSB0 but commands like
AT*CNTI=0 only give output on ttyUSB2.

Hope that's the information you're looking for.

Best regards, Ralf

On Tue, 17 Mar 2009, Rory Filer wrote:

> Hi Ralf,
>
> I wonder whether you could do a little experiment for me. Issue the following AT command to both ports you've identified:
>
> ATI
>
> And note which of the AT ports provides the most information. They will both respond, but one will be more verbose than the others.
>
> Another thing of interest is to record how many files appear in response to the following command:
>
> ls /dev/ttyU*
>
> when the modem is running, of course.
>
> Question - at what point should we stop including linux-kernel in this thread, if at all?
>
> Regards
>
> Rory
>
> -----Original Message-----
> From: Ralf Nyren [mailto:ralf@xxxxxxxxx]
> Sent: Tuesday, March 17, 2009 8:54 AM
> To: Rory Filer
> Cc: Greg KH; Stephen Clark; linux-kernel@xxxxxxxxxxxxxxx; Kevin Lloyd
> Subject: RE: Sierra Wireless (MC8780) HSDPA speed issue
>
> Hi again,
>
> Problem solved this time, well sort of anyway.
>
> This is a bit embarrassing, was quite sure I had tested this before but oh well...
>
> According to the FAQ at sierrawireless.com you should make the data connection
> on /dev/ttyUSB2 when using a MC8780 modem, /dev/ttyUSB0 is used for AT commands
> queries. This works nicely except for the speed problem. Now _changing_ so the
> data connection is established on /dev/ttyUSB0 instead solves the speed
> problem. I have successfully reached average download speeds above 400KB/s.
>
> Just to make sure I tried this fix using both 1.3.2 and 1.6.0 driver. I also
> tried the modified ppp_async.c with OBUFSIZE=4096. The cell appeared to be
> rather busy during the tests but as far as I can see both drivers and OBUFSIZE
> gave about the same speed, i.e. 300-400KB/s at my current location. No issue
> with the kernel that is.
>
> My only remaining problem is that I can't issue commands like AT+CSQ, AT+COPS?
> to determine signal strength and ISP while the connection is up and running.
> Any AT command sent to /dev/ttyUSB2 while pppd runs on /dev/ttyUSB0 causes an
> immediate modem hangup. Not a big issue but it would be nice if it worked.
>
> The card is a builtin card in the laptop and all tests reported so far have
> been performed with the same machine. Have a dual boot setup with Debian Lenny
> and Windows XP. Firmware on the MC8780 card is reported as follows:
>
> AT+GMR
> F1_0_0_10AP C:/WS/FW/F1_0_0_10AP/MSM7200R3/SRC/AMSS 2007/11/08 10:51:15
> OK
>
> If you think this problem could affect others as well an update to the table on
> the FAQ page would be nice:
>  http://www.sierrawireless.com/faq/ShowFAQ.aspx?ID=607
>
> Thanks for all valuable help and support. Just let me know if you need someone
> to test future firmware/driver updates.
>
> Best regards, Ralf
>
>
> On Mon, 16 Mar 2009, Rory Filer wrote:
>
> > Hi Ralf,
> >
> > Actually the Windows and Linux models are the same from the modem's point of view, but the PPP client is inside the NDIS driver.
> >
> > I've pasted in the response from our UMTS engineer below, but I'm not sure how much help it will be; here it is:
> >
> > -----Begin Included...
> > There is no specific AT command that would limit the data rate on the device - except for AT!HSDCAT but I do not think that he would be using this. Other commands such as AT+CGEQREQ probably would not help, so they should clear them.
> >
> > From the email below it seems that he used the same device on Windows so the device configuration should be OK. The location could be an issue but I would assume that he tried using the device with Windows at the same location.
> >
> > One problem that I have seen with USB is that the USB modem throughput will be low if there are other devices on the same USB hub of the laptop
> > ----End Included
> >
> > There it is. If you could get your hands on another machine and put Linux on it - or maybe temporarily make your windows machine into Dual Boot with Ubuntu (using wubi) and see how that compares that might help, but I am out of useful ideas at this point.
> >
> > Regards
> >
> > Rory
> >
> >
> >
> > -----Original Message-----
> > From: Ralf Nyren [mailto:ralf@xxxxxxxxx]
> > Sent: Monday, March 16, 2009 5:48 AM
> > To: Greg KH
> > Cc: Rory Filer; Stephen Clark; linux-kernel@xxxxxxxxxxxxxxx; Kevin Lloyd
> > Subject: Re: Sierra Wireless (MC8780) HSDPA speed issue
> >
> > Thanks Rory,
> >
> > I have tried changing OBUFSIZE in ppp_async.c (still kernel 2.6.28.7), first
> > 512 and then 4096. However the speed "limit" of about 100KB/s remains the same.
> > So perhaps there's some setup/firmware issue with the hardware. If I understand
> > things correctly the Windows driver uses a proprietary protocol to init the card
> > while in Linux you use the AT command interface. Could be something there which
> > makes a difference I guess.
> >
> > Best regards, Ralf
> >
> > On Sun, 15 Mar 2009, Greg KH wrote:
> >
> > > On Sun, Mar 15, 2009 at 03:30:54PM -0700, Rory Filer wrote:
> > > > Hi Ralf
> > > >
> > > > Using the driver we sent you on a call-box (i.e. with a "perfect"
> > > > simulated network connection) on Ubuntu 8.04 we were seeing ~4 Mbps on
> > > > the downlink. So I would rule out any problem with the driver and
> > > > conclude it must be something in either PPP/Linux or in the modem. In
> > > > order to rule out the modem, I've got a question into one of our UMTS
> > > > engineers and will send you a reply when we get the answer.
> > > >
> > > > We did play around a little with 2.4 kernels of Linux and discovered
> > > > there is a buffer in PPP_ASYNC.C which, when its size is increased,
> > > > doubled the throughput. If you are savvy enough with Linux, you might
> > > > want to try playing with that. We stopped short of any thorough
> > > > testing of changing this array size, but were pleased with the result.
> > > > If I recall properly, the size of this array is (was, in 2.4) 256
> > > > bytes. Doubling it gave an immediate improvement. We were guessing
> > > > that the small size of this buffer was fine in the "old days" when
> > > > modems peaked at ~56 kbps. Even 8 years ago that was the fastest you
> > > > could go with a GPRS product, now our new HSPA+ products yields 21
> > > > Mbps on Telstra's network! Quite a difference.
> > >
> > > Ah, the OBUFSIZE #define in drivers/net/ppp_async.c?
> > >
> > > Anyone care to bump this size up and see if that helps out?
> > >
> > > thanks,
> > >
> > > greg k-h
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