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RELEASED
DATA SHEET
PM7366 FREEDM-8
ISSUE 4
PMC-1970930
FRAME ENGINE AND DATA LINK MANAGER
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA,INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
39
Receive Packet Descriptor
The Receive Packet Descriptors (RPDs) pass buffer and packet information between the RMAC
and the host. Both the RMAC 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
RMAC 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
Reserved (18)
CE
Next RPD Pointer [13:0]
Status [5:0]
RCC [6:0]
Data Buffer Start Address [31:0]
Receive Buffer Size [15:0]
0
Bit 31
Bytes In Buffer [15:0]
Reserved (16)
Offset[1:0]
Table 8 – Receive Packet Descriptor Fields
Field
Description
Data Buffer Start
Address[31:0]
The Data Buffer Start Address[31:0] bits point to the data buffer in host
memory. This field is expected to be configured by the Host during
initialisation.
The Data Buffer Start Address field is valid in all RPDs.
RCC[6:0]
The Receive Channel Code (RCC[6:0]) bits are used by the RMAC to
indicate which channel an RPD is associated with.
For a linked list of RPDs, all the RPDs’ RCC fields are valid, i.e. all
contain the same channel value.
CE
The Chain End (CE) bit indicates the end of a linked list of RPDs.
When CE is set to logic one, the current RPD is the last RPD of a
linked list of RPDs. When CE is set to logic zero, the current RPD is
not the last RPD of a linked list.
The CE bit is valid for all RPDs written by the RMAC to the Receive
Ready Queue. When a packet requires only one RPD, the CE bit is
set to logic one. The CE bit is ignored for all RPDs read by the RMAC
from the Receive Free Queues, each of which is assumed to point to
only one buffer, i.e. not a chain.