Receiving Zeros via SPDIF with STM32F446 does not work

[BSchm.6]

I'm using an STM32F446RE to receive data via SPDIF. This works well with the following initialisation:

hspdif.Instance = SPDIFRX;
  hspdif.Init.InputSelection = SPDIFRX_INPUT_IN0;
  hspdif.Init.Retries = SPDIFRX_MAXRETRIES_15;
  hspdif.Init.WaitForActivity = SPDIFRX_WAITFORACTIVITY_ON;
  hspdif.Init.ChannelSelection = SPDIFRX_CHANNEL_A;
  hspdif.Init.DataFormat = SPDIFRX_DATAFORMAT_MSB;
  hspdif.Init.StereoMode = SPDIFRX_STEREOMODE_ENABLE;
  hspdif.Init.PreambleTypeMask = SPDIFRX_PREAMBLETYPEMASK_OFF;
  hspdif.Init.ChannelStatusMask = SPDIFRX_CHANNELSTATUS_OFF;
  hspdif.Init.ValidityBitMask = SPDIFRX_VALIDITYMASK_OFF;
  hspdif.Init.ParityErrorMask = SPDIFRX_PARITYERRORMASK_OFF;
  if (HAL_SPDIFRX_Init(&hspdif) != HAL_OK)

...and with the following code (just some snippets to demonstrate what is going on):

void HAL_SPDIFRX_RxCpltCallback(SPDIFRX_HandleTypeDef *hspdif)
{
	spdifRecvComplete=1;
}
 
...
 
  if (HAL_SPDIFRX_ReceiveDataFlow_IT(&hspdif,recvBuffer[currBuff],spdifBufferSize)==HAL_OK)
  {
     spdifRecvComplete=0;
     currBuff=1-currBuff;
  }
 
...
 
  while (1)
  {
      if (spdifRecvComplete)
      {
         if (HAL_SPDIFRX_ReceiveDataFlow_IT(&hspdif,recvBuffer[1-currBuff],spdifBufferSize)==HAL_OK)
         {
            spdifRecvComplete=0;
...

Within my recvBuffer I can see the received audio data in the upper 20 bits and the flags/auxiliary bits in the lower 12 bits of the 32bit received data.

But when the incoming data except the Valid-bit all are 0 (means the device on the other end has 0 at Aux, Data and the flags except "Valid"), the interrupt never happens. The preamble of course is still valid, so that proper frames can be detected:

 

So shouldn't this also cause an interrupt to occur when there are enough SPDIF-frames detected? Or is there something special needed in order to receive such 0-data-frames too?

Thanks 

[waclawek.jan]

My SPDIF-fu is rusty, but SPDIF is more than just data, you should also see proper pattern of the preambles, to be able to identify individual blocks. I believe the SPDIF-RX chapter in RM0390 has a quite concise description of the protocol and also how the module indicates various correct and incorrect states.

Cube/HAL and Cube-MX-clicked-code usually does not work well with anything other than usual/expected.

JW

[BSchm.6]

From SPDIF-frame's point of view it should be fine, there are valid preambles, the "valid"- and the "parity"-bits are set properly. Just the payload is completely at 0 (including user-, control-bit, data and auxiliary).

[waclawek.jan]

Well, I don't know answers to your problem, but I'd recommend you to

• read the SPDIF chapter in RM
• read and output in real-time the available status information (SPDIFRX_SR)
• make sure you can map between the Cube/HAL nomenclature and actions, and the RM's nomenclature and description; or simply avoid using Cube/HAL

JW

[LCE]

What is your SPDIF source?

I use the SAI SPDIF TX a lot for testing, which is working very reliably, you might try that as a source.

It might be that an idle SPDIF source is sending always zeros, just to let the receiver keep the sync. So maybe there is some setting / bit register on the STM's RX side how to react to an ongoing zero-only input?