Hi Iulia, On Fri, Mar 3, 2023 at 7:02 AM Iulia Tanasescu <iulia.tanasescu@xxxxxxx> wrote: > > Hello, > > Earlier this week I submitted a BlueZ patch ([1]) containing an initial implementation of the Broadcast Audio Scan Service. > > In order to perform some of the BASS procedures, the BASS Server is required to send specific HCI commands and to handle HCI events accordingly - for example, the "Set Broadcast_Code" operation of the Broadcast Audio Scan Control Point characteristic requires the BASS Server to issue the LE BIG Create Sync command with the Broadcast_Code parameter set to the characteristic value written by the BASS Client. > > My approach was to open an HCI socket and to send the command directly from the BASS handler function. After my proposed implementation was reviewed, I was told I should use an ISO socket instead and let the Bluetooth kernel perform the BIG synchronization procedure. I investigated this solution and the problem that I encountered was that the kernel sends HCI commands with fixed parameters - calling the "listen" API on an ISO socket will always attempt to send the LE BIG Create Sync command with the Broadcast_Code parameter set to 0. I couldn't find a way to provide my desired parameters to the HCI command. > > I also discovered 2 kernel issues when calling "listen" on an ISO socket: > > The first issue is that the "hci_pa_create_sync" function attempts to send the LE Periodic Advertising Create Sync command with the Sync_Timeout parameter set to 0 - according to the Bluetooth Core specification version 5.3, this parameter should be in the 0x000A - 0x4000 range. This is why the Controller will reject this command, as shown in the following btmon capture: > > > < HCI Command: LE Periodic Advertising Create Sync (0x08|0x0044) plen 14 > Options: 0x0000 > Use advertising SID, Advertiser Address Type and address > Reporting initially enabled > SID: 0x01 > Adv address type: Public (0x00) > Adv address: C0:07:E8:8B:69:F2 (OUI C0-07-E8) > Skip: 0x0000 > Sync timeout: 0 msec (0x0000) > Sync CTE type: 0x0000 > > > HCI Event: Command Status (0x0f) plen 4 > LE Periodic Advertising Create Sync (0x08|0x0044) ncmd 1 > Status: Invalid HCI Command Parameters (0x12) > > Updating the "hci_pa_create_sync" function and setting the "sync_timeout" field of the command parameters to a value in the required range solves the problem. Broadcast support is in its very early stages of development, and yes the sync_timeout probably need fixing as it using invalid range right now, we should probably a way to configure it via use of BT_ISO_QOS, currently both unicast and broadcast are using the same structure but perhaps it would be a good idea to differentiate them with more dedicated options. > The same issue appears when the kernel attempts to send the LE BIG Create Sync command with the BIG_Sync_Timeout parameter set to 0: > > > < HCI Command: LE Broadcast Isochronous Group Create Sync (0x08|0x006b) plen 25 > BIG Handle: 0x00 > BIG Sync Handle: 0x0000 > Encryption: Encrypted (0x00) > Broadcast Code: 00000000000000000000000000000000 > Maximum Number Subevents: 0x00 > Timeout: 0 ms (0x0000) > Number of BIS: 1 > BIS ID: 0x01 > > > HCI Event: Command Status (0x0f) plen 4 > LE Broadcast Isochronous Group Create Sync (0x08|0x006b) ncmd 1 > Status: Parameter Out Of Manadatory Range (0x30) > > Updating the "hci_le_big_create_sync" function and setting the "timeout" field of the command parameters to a valid value solves the issue. Patches are welcome to fix this as well. > Hopefully someone can confirm the kernel issues I described and the fixes can be committed. I would also like to ask for some guidance regarding the ISO socket usage when it comes to personalizing HCI command parameters - is there a way to set the parameters from BlueZ? Or should this support be implemented in the Bluetooth kernel? The setup of Qos is done via BT_ISO_QOS: https://git.kernel.org/pub/scm/linux/kernel/git/bluetooth/bluetooth-next.git/tree/include/net/bluetooth/bluetooth.h#n174 As you can see currently the structure is targeting unicast parameters, we should probably split this and have a dedicated one for broadcast. > Thank you in advance > > Iulia > > [1] [BlueZ,0/2] Add initial BASS support - Patchwork (kernel.org) > -- Luiz Augusto von Dentz
