7.7.5.2 Limitations

The frequency ratio GCLK/peripheral clock must be lower than 4.

The frequency of the GCLK clock is determined by the maximum value of the input and output sampling frequencies.

When up-sampling, the maximum ratio between output and input sampling frequencies is 16. When down-sampling, the max ratio is 12.

In Direct Access mode, the minimum frequency required on the peripheral clock depends on the highest rate of all the audio streams processed with the ASRC. The minimum frequency must be greater than Number_of_Samples x Sampling_Frequency × 46 (ASRC constant).

As an example, when a 48 Ksps stereo stream is processed, the frequency of the peripheral clock must be greater than 48 × 2 × 46 MHz, and thus greater than 4.5 MHz. For a TDM with 8 channels at 192 Ksps, the minimum peripheral clock frequency increases up to 192 × 8 × 46 MHz, thus greater than 71 MHz.