TAS5825M: Is SDOUT in "DSP input (pre-processing)" mode supposed to pass all TDM channels from SDIN to SDOUT?

Daniel Germann1

Part Number: TAS5825M
Other Parts Discussed in Thread: TAS5754M

We have hardware that uses two TAS5825M amplifiers. Our CPU is generating an 8-channel TDM audio stream, with the first 4 slots filled with audio data. Slots 1 and 2 are for the first amplifier, and slots 3 and 4 are for the second amplifier.

On both amplifiers, we have GPIO0 configured as FAULTZ, GPIO1 configured as MUTEZ and GPIO2 configured as SDOUT. Register 60H is set to 05H (GPIO0 and GPIO2 are outputs), register 61H is set to 0BH (GPIO0 is FAULTZ), register 63H is set to 09H (GPIO2 is SDOUT) and register 64H is set to 02H (MUTEZ on GPIO1).

SDOUT from our CPU goes to SDIN on first TAS5825M. On this amplifier, register 30H is set to 01H (SDOUT is the DSP input), register 33H is set to 13H (TDM, 32-bit word length), and register 34H is set to 00H (no offset).

SDOUT from first TAS5825M goes to SDIN on second TAS5825M. On this amplifier, register 30H is set to 01H (SDOUT is the DSP input), register 33H is set to 13H (TDM, 32-bit word length), and register 34H is set to 40H (offset 64 SCLKs).

This configuration is similar to what is shown in Figure 8-9 in the TAS5825M datasheet.

We loaded the CFG file generated by PurePathConsole3 into each amplifier, and then set the registers described above before putting the amplifier into PLAY mode (by setting register 03H to 03H).

We can see data in the first four slots going into SDIN on the first TAS5825M, which is correct. But SDOUT only has audio in the first two slots. We have done this same thing with the TAS5754M, and all four slots of audio pass through the first amplifier to the second amplifier. But we are not seeing this behavior on the TAS5825M.

Are we misunderstanding how this works? Or are we missing a configuration setting somewhere?

Thank you!
-Dan

over 4 years ago

0 Luis Fernandes de Pina over 4 years ago

TI__Genius 15200 points

Hello Dan,

Can you clarify what you are trying to do with SDOUT? The post-processed data will the slots that device's DSP sees.

Best regards,

Luis

0 Daniel Germann1 over 4 years ago in reply to Luis Fernandes de Pina

Prodigy 130 points

On several previous designs, we used the amplifier's SDOUT pin to pass the incoming audio to the next amplifier.

CPU SDOUT -> AMP1 SDIN ; AMP1 SDOUT (pre-DSP) -> AMP2 SDIN ; AMP2 SDOUT (pre-DSP) -> AMP3 SDIN ...etc...

We did this with the TAS5754M and had no problems. It was nice because we had a single point-to-point connection from each SDOUT to the next SDIN. Very clean signal flow. But it does not seem to work on the TAS5825M.

We can change the PCB to route the CPU SDOUT to the SDIN on all amplifiers, but if there is a way to make the SDOUT pass exactly what came in on SDIN (like the TAS5754M does), that would be helpful.

0 Luis Fernandes de Pina over 4 years ago in reply to Daniel Germann1

TI__Genius 15200 points

Hello Daniel,

Are you encountering this even when SDOUT_SEL(0x30) is configured as DSP input?

best regards,

Luis

0 Daniel Germann1 over 4 years ago in reply to Luis Fernandes de Pina

Prodigy 130 points

Yes, register 30H is set to 01H (SDOUT is the DSP input). Looking at SDIN of the first amplifier with an oscilloscope, we can see data in TDM slots 1, 2, 3 and 4. But at the first amplifier's SDOUT, we only see data in TDM slots 1 and 2. In case it helps you, in my first message I included a description of all the register settings we changed after loading the CFG file produced by PPC3.

Would you expect to see data in all 4 TDM slots at SDOUT with SDOUT_SEL configured as the DSP input?

Thank you, Luis!

0 Luis Fernandes de Pina over 4 years ago in reply to Daniel Germann1

TI__Genius 15200 points

Hello Daniel,

I'm confirming a few items with our team in regards to the expected TDM configuration, I will provide an update tomorrow. However, typically we don't expect a full bypass of all the TDM slots, it would probably be recommended to have a shared TDM input bus but I am trying to clarify this point with the digital team.

Best regards,

Luis

0 Daniel Germann1 over 4 years ago in reply to Luis Fernandes de Pina

Prodigy 130 points

Hi, Luis.

Have you been able to find out any more information about this?

Thank you,

-Dan

+1 Luis Fernandes de Pina over 4 years ago in reply to Daniel Germann1

TI__Genius 15200 points

Hello Dan,

For the TDM configuration for the TAS58xx, the SDOUT only has the slots that the device is configured for. It's only the two slots so you will need to do a shared TDM input bus instead of your previous configuration of fanning SDOUT between devices.

Best regards,

Luis

0 Daniel Germann1 over 4 years ago in reply to Luis Fernandes de Pina

Prodigy 130 points

Thanks, Luis. We will change the PCB layout to support a shared TDM bus then.

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TAS5825M: Is SDOUT in "DSP input (pre-processing)" mode supposed to pass all TDM channels from SDIN to SDOUT?