Hi,

I have digged some further into this and found out the following:

Just after pairing the headset l2ping shows ping times of about 45 msec.
After starting btsco and about 5 sec after btsco has connected hcidump
shows:


1152107748.832103 < ACL data: handle 42 flags 0x02 dlen 9
    L2CAP(d): cid 0x0042 len 5 [psm 3]
      RFCOMM(d): UIH: cr 1 dlci 2 pf 1 ilen 0 fcs 0x86 credits 33
1152107748.835034 > ACL data: handle 42 flags 0x02 dlen 9
    L2CAP(d): cid 0x0041 len 5 [psm 3]
      RFCOMM(d): UIH: cr 0 dlci 2 pf 1 ilen 0 fcs 0x5c credits 15
1152107748.840034 > HCI Event: Number of Completed Packets (0x13) plen 5
1152107754.511244 > HCI Event: Mode Change (0x14) plen 6


After this last 'Mode Change' is received l2ping takes 4000-6000 msec
which corresponds to the delay in starting audio playback.

Additionally the hcidump for l2ping -c1 looks different (btsco running):

This is before we receive HCI Event: Mode Change (0x14) plen 6:


1152108661.495583 < ACL data: handle 43 flags 0x02 dlen 52
    L2CAP(s): Echo req: dlen 44
1152108661.516393 > HCI Event: Number of Completed Packets (0x13) plen 5
1152108661.546387 > ACL data: handle 43 flags 0x02 dlen 27
1152108661.548386 > ACL data: handle 43 flags 0x01 dlen 25
    L2CAP(s): Echo rsp: dlen 44


and this after we received HCI Event: Mode Change (0x14) plen 6:


1152106935.430096 < ACL data: handle 42 flags 0x02 dlen 52
    L2CAP(s): Echo req: dlen 44
1152106936.918474 > HCI Event: Number of Completed Packets (0x13) plen 5
1152106939.474570 > ACL data: handle 42 flags 0x02 dlen 17
1152106939.476566 > ACL data: handle 42 flags 0x01 dlen 17
1152106939.477589 > ACL data: handle 42 flags 0x01 dlen 17
1152106939.478582 > ACL data: handle 42 flags 0x01 dlen 1
    L2CAP(s): Echo rsp: dlen 44


can anybody tell me what this 'HCI Event: Mode Change (0x14) plen 6' is
about and probably how to prevent this?

A full hcidump from pairing the headset and starting btsco is attached.

Thanks in advance,
Christoph