This is a summary of the settings required for digital loopback mode for TDM format :
- The MCASP_DLBCTL[0] DLBEN bit must be set to 0b1 to enable a loopback mode. It must be kept at 0b0 during normal MCASP operation.
- The MCASP_DLBCTL[4] IOLBEN bit must be set to select between internal (MCASP local) loopback mode or device I/O level loopback mode.
- The MCASP_DLBCTL[3-2] MODE bit field must be set to 0x1 for both the transmit and receive sections to use the transmit clock and frame sync generator.
- The MCASP_DLBCTL[1] ORD bit must be programmed appropriately to select odd or even serializers to be transmitters or receivers.
- The corresponding serializers must be configured accordingly.
- The MCASP_ACLKXCTL[6] ASYNC bit must be cleared
to 0b0 to ensure synchronous transmit and receive operations.
- The MCASP_AFSRCTL[15-7] RMOD bit field and MCASP_AFSXCTL[15-7] XMOD bit field must be set within range (0x2 - 0x20) to indicate TDM mode.
Note: Loopback mode does not apply to DIT or burst mode, because MCASP receivers do NOT natively support DIR - reception.