7.7.5.12.2 Bridging Without Rate Conversion

It is possible to connect a receive audio peripheral directly to a transmit audio peripheral without rate conversion (no DSP intervention) when both the receive and transmit audio peripherals are driven by the same clock source and are the hosts of their respective external audio lines. Up to four direct bridging links can be enabled independently.

Note: For correct synchronization, the system must either provide the reference clock to the external device generating the audio stream, or the receiver may also propagate the reference clock via control signals such as frame synchronization, etc.

The Direct Access mode must be configured for both the receive and transmit channels (see ASRC_MR) and the audio peripherals to be coupled must be configured in ASRC_DAPSELR. The bridging link is enabled by configuring the Direct Access Bridge Mode register (ASRC_DABMR).

When a bridging link is enabled, according to the configuration of other links, one or more DSPs may not be required and can be disabled by writing ASRC_MR.ASRCENx=0 to reduce power consumption (see the following figure).

Figure 7-73. Example of One Channel Direct Bridging without Rate Conversion

A direct bridging link can be enabled at the same time as a link involving all DSPs for rate conversion (see the following figure).

Figure 7-74. Example of One Channel Direct Access Bridging in Parallel with Channel Rate Conversion

When a direct bridging link operates a mono audio stream, ASRC_DABMR.BRMONOx must be written to 1.