Subject: Re: [Bluez-devel] Problem of data loss with a particular dongle
	brand
From: Marcel Holtmann <marcel@holtmann.org>
To: bluez-devel@lists.sourceforge.net
In-Reply-To: <8c9e090512161013h6782f187k@mail.gmail.com>
References: <8c9e090512161013h6782f187k@mail.gmail.com>
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Date: Fri, 20 Jan 2006 02:47:54 +0100

Hi Elvis,

unfortunately the original messages did make it to the list.

> I suffered a problem with data loss in RFCOMM connections, but I
> managed to discover that it just happens when a cheapo dongle I have
> is in the *receiving* side. I have 2 exactly equal dongles and both
> cause the same problem.
> 
> It happens when the sender sends a big buffer at once (> 1500 bytes).
> If the server makes repeated cals to send() with around 500 bytes
> each, the problem does not happen.  Perhaps the hardware is flawed
> and/or perhaps Bluez is not handling this dongle correctly.
> When both sides are "good" BT interfaces, (either Bluez or
> smartphone), problem does not happen also.
> 
> I am attaching the hcidump -X sessions of communication with the
> problem (bad dongle and good BT interface sides), as well the Python
> scripts that are my guinea pigs for these tests.
> 
> root@dosmtc17:/bkpz # hciconfig -a
> hci0:   Type: USB
>         BD Address: 00:11:67:04:D2:32 ACL MTU: 678:8  SCO MTU: 48:10
>         UP RUNNING PSCAN ISCAN
>         RX bytes:3610 acl:17 sco:0 events:190 errors:0
>         TX bytes:59930 acl:129 sco:0 commands:25 errors:0
>         Features: 0xff 0xff 0x8d 0x78 0x08 0x18 0x00 0x00
>         Packet type: DM1 DM3 DM5 DH1 DH3 DH5 HV1 HV2 HV3
>         Link policy: RSWITCH HOLD SNIFF PARK
>         Link mode: SLAVE ACCEPT
>         Name: 'dosmtc17-0'
>         Class: 0x100100
>         Service Classes: Object Transfer
>         Device Class: Computer, Uncategorized
>         HCI Ver: 1.2 (0x2) HCI Rev: 0x1ae LMP Ver: 1.2 (0x2) LMP Subver: 0x1ae
>         Manufacturer: Integrated System Solution Corp. (57)

I actually never really found the reason why the ISSC dongles are so
damn crappy. Maybe their USB interface is broken. Try to load the
hci_usb driver with isoc=0 to disable the SCO support and its ISOC
transfers.

Regards

Marcel


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