SPRUIU1C July 2020 – February 2024 DRA821U , DRA821U-Q1
The CPRGMII transmit (TX) interface converts the CPGMAC G/MII input data into the DDR RGMII format. The DDR data is then output to the external PHY.
The CPGMAC does not source the transmit error (TXERR) signal. Any transmit frame from the CPGMAC with an error (underrun) will be indicated as an error by an error CRC. Transmit error is assumed to be deasserted at all times and is not an input into the CPRGMII module.
In 10/100 Mbps mode, the TXD[7:0] data bus uses only the lower nibble. The CPRGMII will output the lower nibble twice in 10/100 Mbps mode to avoid unnecessary signal switching.
Packets will be precluded from transmission through the CPRGMII module for 4096 transmit clocks after the rising edge of RGMII_LINK. Packet transmission will begin on the first TX_CTL rising edge after the 4096 transmit clock count has expired.