SPRUIU1C July 2020 – February 2024 DRA821U , DRA821U-Q1
The CPRMII receive (RX) interface converts the input data from the external RMII PHY (or switch) into the required MII (CPGMAC) signals. The carrier sense and collision signals are determined from the RMII input data stream and transmit inputs as defined in the RMII specification.
An asserted RMII_RXER on any di-bit in the received packet will cause an MII_RXER assertion to the CPGMAC during the packet. In 10Mbps mode, the error is not required to be duplicated on 10 successive clocks. Any di-bit which has an asserted RMII_RXER during any of the 10 replications of the data will cause the error to be propagated.
Any received packet that ends with an improper nibble boundary aligned RMII_CRS_DV toggle will issue an MII_RXER during the packet to the CPGMAC. Also, a change in speed or duplex mode during packet operations will cause packet corruption.
The CPRMII can accept receive packets with shortened preambles, but 0x55 followed by a 0x5D is the shortest preamble that will be recognized (1 preamble byte with the start of frame byte). At least one byte of preamble with the start of frame indicator is required to begin a packet. An asserted RMII_CRS_DV without at least a single correct preamble byte followed by the start of frame indicator will be ignored.