What are Loopback Pin buffers ?
Loopback Pin buffers are provided to route back the clock signals into the DAI blocks which are transmitted as output signals from the chip.
Four loopback pin buffers are provided per DAI block which are connected to DAI pins 3/4/5/6 respectively.
Inputs to each loopback pin are same as respective DAI pin buffer’s input.
Output of Loopback pin buffer’s are muxed with the DAI Pin buffer’s output and based on the respective Pads output enable signal either DAI pin buffer output is selected or Loopback Pin buffer output is selected. When the DAI pin buffer is configured for output then the mux output will be always the Loopback pin buffer’s output else it will be DAI pin buffers output.
Below diagram describes the connections of dummy pins buffers in DAI sub-system.
Note: Loopback pin buffers are applicable only when DAI pins are configured when clock is output and FS/data are inputs.
Loopback Pin buffer Connection example
The SPORT0A clock is an output and transmitted as an output on DAI Pin4. This SPORT0A is configured where it transmits clock and receives data. Received data is sampled w.r.t the transmitted clock which is routed back to the SPORT0A through the loopback pin buffer.