i.MX ProcessorsのトピックRe: SAI driver TDM slot shuffling

SAI driver TDM slot shuffling

rajeshkorabandi — Mon, 15 Jul 2024 10:53:53 GMT

Hi All,

I am seeing an issue with TDM data slot mapping in my Audio system.

in my System the IMX8 is transferring the data to Audio Card over SAI interface.

the Audio card has 8-TDM lines and 2-slots per TDM line.

i am seeing different TDM line allocation and TDM slots for the same channel when the number of channels programmed in alsa is different

when i have a 4-channel design , i set the number of channels to alsa to 4 through alsa API. In this case the TDM line number and TDM slot number are allocated like the following.

Audio Card Channel	TDM Line Number	TDM Slot Number
0	0	0
1	1	0
2	0	1
3	1	1

In case of 16-channel design . i set the number of channels to alsa to 16 through alsa API. In this case the TDM line number and TDM slot number are allocated like the following .

Audio Card Channel	TDM Line Number	TDM Slot Number
0	0	0
1	1	0
2	2	0
3	3	0
4	4	0
5	5	0
6	6	0
7	7	0
8	0	1
9	1	1
10	2	1
11	3	1
12	4	1
13	5	1
14	6	1
15	7	1

As you can see The TDM line Allocation for channels are different in different scenarios.

in 4-channel design

channel 2 is allocated to TDM line 0 and TDM slot-1

in 16-channel design

Channel 2 is allocated to TDM line 2 and TDM slot-0

this discrepancy is causing a problem when i dynamically change the number of channels in alsa.

i want to see the SAI driver allocation like this

CPU Card Channel	TDM Line Number	TDM Slot Number
0	0	0
1	0	1
2	1	0
3	1	1
4	2	0
5	2	1
6	3	0
7	3	1
8	4	0
9	4	1
10	5	0
11	5	1
12	6	0
13	6	1
14	7	0
15	7	1

Could you someone suggest me how to get this allocation in the fsl_sai.c driver ?

Re: SAI driver TDM slot shuffling

rajeshkorabandi — Thu, 18 Jul 2024 13:46:14 GMT

can someone help with this problem?

Re: SAI driver TDM slot shuffling

JorgeCas — Thu, 18 Jul 2024 19:52:13 GMT

Hello,

I apologize for the delayed reply.

Our documentation does not show how are configured audio channels on TDM line/slot. On reference manual, it is described an example for 8 channels:

On source code, is mentioned here. But is not too clear about how is done.

Could you please share me which OS version and processor are you using?

Best regards.

Re: SAI driver TDM slot shuffling

rajeshkorabandi — Fri, 19 Jul 2024 09:25:37 GMT

Thank you Jorge .

Here is the configuration

Linux version -
4.14.98imx_4.14.98_2.0.0

CPU - imx8MM

Re: SAI driver TDM slot shuffling

JorgeCas — Fri, 19 Jul 2024 18:17:57 GMT

Hello,

Thank you for the information, as I mentioned before, is not too clear in documentation how this is configured. I will check internally where is configured or if it is hardcoded to move forward on this matter.

I will update you as soon as possible.

Best regards.

Re: SAI driver TDM slot shuffling

JorgeCas — Tue, 23 Jul 2024 14:50:08 GMT

Hello,

According to internal team, this is defined on device tree:

dai-tdm-slot-tx-mask : Transmit direction slot mask, optional
dai-tdm-slot-rx-mask : Receive direction slot mask, optional

There is a .of_xlate_tdm_slot_mask() to specify an explicit mapping of the channels and the slots. If it's absent the default snd_soc_of_xlate_tdm_slot_mask() will be used to generating the tx and rx masks.

Best regards.

Re: SAI driver TDM slot shuffling

rajeshkorabandi — Tue, 23 Jul 2024 15:16:42 GMT

Thank you. i will make changes in the kernel and update you with my results