PM7384 FREEDM-84P672
DATA SHEET
PMC-1990445
ISSUE 5
FRAME ENGINE AND DATA LINK MANAGER 84P672
places the associated RPDR onto a RPDR ready queue. To minimize host bus
accesses, the RMAC672 maintains a descriptor reference table to store current
DMA information. This table contains separate DMA information entries for up to
672 receive channels.
9.6.1 Data Structures
For packet data, the RMAC672 communicates with the host using Receive
Packet Descriptors (RPD), Receive Packet Descriptor References (RPDR), the
Receive Packet Descriptor Reference Ready (RPDRR) queue and the Receive
Packet Descriptor Reference Small and Large Buffer Free (RPDRF) queues.
The RMAC672 copies packet data to data buffers in host memory. The RPD,
RPDR, RPDRR queue, and Small and Large RPDRF queues are data structures
which are used to transfer host memory data buffer information. All five data
structures are manipulated by both the RMAC672 and the host computer. The
RPD holds the data buffer size, data buffer address, and packet status
information. The RPDR is a pointer which is used to index into a table of RPDs.
The RPDRR queue and RPDRF queues allow the RMAC672 and the host to
pass RPDRs back and forth. These data structures are described in more detail
in the following sections.
Receive Packet Descriptor
The Receive Packet Descriptors (RPDs) pass buffer and packet information
between the RMAC672 and the host. Both the RMAC672 and the host read and
write information in the RPDs. The host writes RPD fields which describe the
size and address of data buffers in host memory. The RMAC672 writes RPD
fields which provide number of bytes used in each data buffer, RPD link
information, and the status of the received packet. RPDs are stored in host
memory in a Receive Packet Descriptor Table which is described in a later
section. The Receive Packet Descriptor structure is shown in Figure 4.
Figure 4 – Receive Packet Descriptor
Bit 31
0
Data Buffer Start Address [31:0]
Status [5:0]
Reserved (7)
Bytes In Buffer [15:0]
RCC[9:0]
Reserved (16)
Offset[1:0]
CE
Reserved (6)
Res (1)
Next RPD Pointer [14:0]
Receive Buffer Size [15:0]
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