SPRUII0F May 2019 – June 2024 TMS320F28384D , TMS320F28384D-Q1 , TMS320F28384S , TMS320F28384S-Q1 , TMS320F28386D , TMS320F28386D-Q1 , TMS320F28386S , TMS320F28386S-Q1 , TMS320F28388D , TMS320F28388S
The DMA in Ethernet module attempts to read a descriptor only if the Tail Pointer is different from the Base Pointer or current pointer. It is recommended to have a descriptor ring with a length that can accommodate at least two complete packets received by the MAC. Otherwise, the performance of the DMA is impacted greatly because of the unavailability of the descriptors. In such situations, the RxFIFO in MTL becomes full and starts dropping packets.
The following Receive Descriptors are present:
All RX descriptors are prepared by the software and given to the DMA as “Normal” Descriptors with the content as shown in Receive Normal Descriptor (Read Format). The DMA reads this descriptor and after transferring a received packet (or part of) to the buffers indicated by the descriptor, the Rx DMA closes the descriptor with the corresponding packet status. The format of this status is given in the “Receive Normal Descriptor (Write-Back Format)”. For some packets, the normal descriptor bits are not enough to write the complete status. For such packets, the RX DMA writes the extended status to the next descriptor (without processing or using the Buffers/ Pointers embedded in that descriptor). The format and content of the descriptor write back is described in Section 43.4.3.3.