Fix incorrect sample reading when `precision == 16` by alternating FIFO sources

[Bianco95]

Description

There is an issue in the data reading logic when precision == 16.

In this configuration, each 32-bit word is split into two 16-bit samples:

• Bits 15:0 → stream_data_fifo
• Bits 31:16 → stream_data_fifo_backup

However, the current implementation reads samples only from stream_data_fifo, causing half of the samples to be skipped.

Current Behavior

When precision == 16:

• Samples are read in the following order:

  • Sample 0, Sample 2, Sample 4, …

• Samples stored in stream_data_fifo_backup are ignored

  • Sample 1, Sample 3, Sample 5, … are never read

This results in incomplete and incorrect data processing.

Expected Behavior

• Samples should be read in the correct order:

  • Sample 0 → stream_data_fifo
  • Sample 1 → stream_data_fifo_backup
  • Sample 2 → stream_data_fifo
  • Sample 3 → stream_data_fifo_backup
  • …

• No samples should be skipped when precision == 16