RE: Sierra Wireless (MC8780) HSDPA speed issue

[Rory Filer]

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
>>
>
>

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/