Return-Path: Message-ID: <406AF150.8080105@csr.com> Date: Wed, 31 Mar 2004 17:26:56 +0100 From: Steven Singer MIME-Version: 1.0 To: Simon Vogl CC: Marcel Holtmann , BlueZ Mailing List Subject: Re: [Bluez-devel] sco / csr final notes References: <406A9E23.9000406@soft.uni-linz.ac.at> <1080730774.2674.6.camel@pegasus> <406AAFFF.6040504@soft.uni-linz.ac.at> <406ADF3E.4020502@csr.com> <406AE027.7030000@soft.uni-linz.ac.at> In-Reply-To: <406AE027.7030000@soft.uni-linz.ac.at> Content-Type: text/plain; charset=windows-1252 List-ID: Simon Vogl wrote: > Steven Singer wrote: >> Is the problem that the link spontaneously changes from correct to noisy >> in the middle of a link, or is it that when you start up a link it's >> either OK for the durection of the link, or noisy for the duration of >> the link and then when you tear it down and start a fresh link, the next >> one is, independently, correct our noisy? >> >> If it's the latter case, is the first link after a full reset (BCCMD >> reset or power cycle - not merely an HCI reset) ever noisy? >> > the latter is the case. Whenever a fresh sco link starts, I have a 50% chance of > getting the wrong byte order.. Assuming it never happens for the first link, then it might be known issue H16.169 (aka. B.104). This is present in 16.4 firmware and is fixed in 16.14. The following is the documentation of this issue from the 16.14 release note (I've marked the relevant section with >>>chevrons<<<): ------------------------------------------------------------------------ Appendix D ? Issues Addressed Relative to HCI 16.4 [...] ID: B.104, H16.169 Severity: High Description: If a system routes HCI SCO channels over USB, there is a high probability that if two SCO channels are opened, and then one of them is closed, then the firmware will crash. This problem has not been seen if only one SCO channel is routed over USB. There is a related, but technically independent, problem. >>>If a USB SCO link is closed, and then a new USB SCO link is opened, it is possible for the second link?s from-air audio to be badly distorted.<<< The audio distortion problem occurs only where both SCO links use 16-bit samples. The distortion occurs where the host does not collect all of the bytes from the last HCI SCO packet of the first SCO link. The second SCO link reuses the first link?s endpoint, and the link?s data incorrectly starts with the first link?s few uncollected bytes. >>>This can be an odd number of bytes, misaligning all subsequent 16-bit samples by one byte.<<< The same audio distortion misalignment can result from a race hazard within the chip, even if the host takes all of the link?s trailing bytes when closing the SCO link. In practice, the race hazard is the primary cause of this problem arising. The distortion issue is similar to issue H13.154, but that issue concerned from-host SCO USB traffic. (HCI builds? release notes have never claimed support for SCO over USB, mainly because of the lack of suitable test equipment, so it is arguable whether this issue should be categorised as being of ?high? importance.) Remedy Both problems have been substantially improved in HCI 16.14. This avoids the issue that causes the chip to crash. The same defensive code also avoids the audio distortion problem. ------------------------------------------------------------------------ I think this confirms your observations. The error is a missing byte and not an endian-ness switch. Upgrading your firmware should fix the problem, otherwise, swallowing a byte when you notice the problem should also ressurect the audio quality. Alternatively, you could always switch to 8 bit samples. Release notes are available on the CSR support web site if you have suitable access permissions. - Steven -- ********************************************************************** The information transmitted is intended only for the person or entity to which it is addressed and may contain confidential and/or privileged material. Any review, retransmission, dissemination or other use of, or taking of any action in reliance upon, this information by persons or entities other than the intended recipient is prohibited. If you received this in error, please contact the sender and delete the material from any computer. **********************************************************************