Re: [Bluez-devel] SCO MTU problem on CSR-based Belkin F8T020/F8T007

[Rich Townsend <rhdt@bartol.udel.edu>]

Marcel Holtmann wrote:
> Hi Rich,
> 
> 
>>I've recently acquired a Belkin F8T020/F8T007 PCMCIA bluetooth interface 
>>(basically, a compact flash card in an adapter sleeve), and I'm trying to get 
>>this linked up to a Digiwave BH-2000 headset.
>>
>>Mostly, everything is functioning correctly; the interface provides a UART on 
>>/dev/ttyS3, which Bluez has no problem working with using the hci_uart driver. 
>>The problem, however, comes in getting the ALSA module, snd_bt_sco, to behave 
>>properly. I can get the headset to connect to my computer, and do things such as 
>>change the volume; but I've had no luck in getting any sound to play on the headset.
>>
>>After a little digging around, it turns out that no SCO packets are being 
>>transmitted by the interface. Closer investigation shows that the problem is 
>>with the outgoing MTU; the len value passed to sco_send_frame is invariably 
>>longer than the default SCO MTU of the interface (64), with the result that 
>>sco_send_frame aborts early with an EINVAL return value (which in turn is 
>>silently ignored).
>>
>>As a test fix, I upped the SCO MTU on the interface to 255, and now stuff 
>>actually gets transmitted -- and I can hear sound on the headset, albeit very 
>>distorted.
>>
>>So, it seems snd_bt_sco is disregarding the MTU settings of the interface. Why, 
>>I'm not sure; a quick look through the snd_bt_sco source code doesn't reveal 
>>anything obvious (in fact, it's not clear how the module picks up the MTU). I'd 
>>appreciate hearing suggestions about how I might go about fixing this.
>>
>>For the record:
>>
>>Kernel 2.6.16 (x86)
>>
>>hciconfig -a (after upping MTU so TX works):
>>
>>hci0:   Type: UART
>>         BD Address: 00:02:72:81:23:27 ACL MTU: 192:8 SCO MTU: 255:8
>>         UP RUNNING PSCAN ISCAN AUTH ENCRYPT
>>         RX bytes:5063515 acl:52 sco:30471 events:94 errors:0
>>         TX bytes:4612824 acl:42 sco:0 commands:27604 errors:0
>>         Features: 0xff 0xff 0x0f 0x00 0x00 0x00 0x00 0x00
>>         Packet type: DM1 DM3 DM5 DH1 DH3 DH5 HV1 HV2 HV3
>>         Link policy: RSWITCH HOLD SNIFF PARK
>>         Link mode: SLAVE ACCEPT
>>         Name: 'BlueZ (0)'
>>         Class: 0x000100
>>         Service Classes: Unspecified
>>         Device Class: Computer, Uncategorized
>>         HCI Ver: 1.1 (0x1) HCI Rev: 0x110 LMP Ver: 1.1 (0x1) LMP Subver: 0x110
>>         Manufacturer: Cambridge Silicon Radio (10)
>>
>>hcitool info 00:13:8A:06:31:0E (the headset):
>>
>>Requesting information ...
>>         BD Address:  00:13:8A:06:31:0E
>>         Device Name: BH2000
>>         LMP Version: 1.2 (0x2) LMP Subversion: 0x611
>>         Manufacturer: Cambridge Silicon Radio (10)
>>         Features: 0xfc 0xfe 0x0f 0x00 0x08 0x08 0x00 0x00
>>                 <encryption> <slot offset> <timing accuracy> <role switch>
>>                 <hold mode> <sniff mode> <RSSI> <channel quality> <SCO link>
>>                 <HV2 packets> <HV3 packets> <u-law log> <A-law log> <CVSD>
>>                 <paging scheme> <power control> <transparent SCO>
>>                 <AFH cap. slave> <AFH cap. master>
>>
>>Big note: both devices are CSR, so this *ISN'T* the well-known MTU problem 
>>experienced by Broadcom chipsets. Smaller note: although the hciconfig output is 
>>after I upped the MTU and got (distorted) sound on the headset, the SCO TX count 
>>is still at zero. Hmmmm....
>>
>>Let me know if you need more info...
> 
> 
> run "hciconfig hci0 revision" as root and see if the SCO mapping is done
> over PCM or HCI.

OK, here's what I get:

hci0:   Type: UART
         BD Address: 00:02:72:81:23:27 ACL MTU: 192:8 SCO MTU: 64:8
         HCI 14.3
         Chip version: BlueCore02-External (ES2)
         Max key size: 56 bit
         SCO mapping:  HCI

As you can see, the mapping is over HCI, so it should work, right?

cheers,

Rich


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