SDAA014 November   2025 AM2752-Q1 , AM2754-Q1

 

  1.   1
  2.   Abstract
  3.   How to Use this Document
  4.   Trademarks
  5. 1Digital Audio Formats
    1. 1.1 I2S
    2. 1.2 TDM
  6. 2McASP Overview
  7. 3McASP Connections for AM275x
    1. 3.1 McASP Common Configurations
      1. 3.1.1 McASP as a Clock Controller
        1. 3.1.1.1 Clocks Generated using the Internal Audio PLL
        2. 3.1.1.2 Clocks Generated using the AUDIO_EXT_REFCLK AUXCLK Source
        3. 3.1.1.3 Clocks Generated using the AUDIO_EXT_REFCLK AHCLK Source
      2. 3.1.2 McASP as Clock Peripheral
        1. 3.1.2.1 Clock Externally Generated with AUDIO_EXT_REFCLK Input
  8. 4McASP Layout Considerations
    1. 4.1 McASP Signals Shared with Bootmode Logic
    2. 4.2 McASP Topology for Multiple Devices in Single Clock Domain
  9. 5ASRC Overview
  10. 6McASP Practical Examples
    1. 6.1 Audio Playback with Internal Audio PLL for Two Clock Domains
    2. 6.2 Audio Playback with External Clock Source and McASP SYNC mode
    3. 6.3 Audio Playback with ASRC Bridging Two Clock Domains
  11. 7Key Audio System Design Takeaways
  12. 8References

5 ASRC Overview

Complex audio systems may require multiple audio zones with different audio clocks. The asynchronous audio sample rate converter (ASRC) module takes samples from one clock zone and translates the audio data to a different clock zone, while maintaining a high signal to noise ratio to ensure that the output audio quality is sufficient to meet the requirements for various high-end audio algorithms. Additionally, the ASRC may be used for converting between two clock domains using the same sampling rate with different root clocks to eliminate clock jitter. For more in-depth information on the ASRC module, refer to the Audio Sample Rate Converter chapter of the AM275x Technical Reference Manual.

The AM275x consists of two ASRC modules and therefore can perform asynchronous sample rate conversion on up to 32 independent audio channels, assuming that each SRC pair can be used for two channels. Figure 6-3 shows an example of how the ASRC can be used in an audio system.

The ASRC module has four input (RXSYNC) and four output (TXSYNC) clock zones that can select from any of the various sample rate options available within the ASRC SYNC muxes. Both RXSYNC and TXSYNC clock zones 0 and 1 have an optional divider that allows for dividing between 1 to 8192. However, if the divider is used for these zones, the input frequency must be less than 96 MHz. If clock zone dividers are not used, then the sample rate must be between 8 and 216 kHz. Additionally, the output clock zone sample rate for any sample rate converter pair must be between the ratio of 1/16 to 16 in relation to the input clock zone sample rate.

Each ASRC module consists of 8 sample rate converter stereo pairs. Each of these pairs can be uniquely configured to use any of the 4 input and output clock zones for sample rate conversion as well as program the input and output word length. Each SRC pair can be configured for mono, stereo, or group channel type. For audio data streams that are larger than two channels, the group channel type can be used to link multiple SRC pairs together with the same timing loop for input and output.

Note: The TXSYNC/RXSYNC clock zone selections, as well as any group channel configurations, are independent across the two ASRC modules.
ASRC Block Diagram Figure 5-1 ASRC Block Diagram