PM7384 FREEDM-84P672
DATA SHEET
PMC-1990445
ISSUE 5
FRAME ENGINE AND DATA LINK MANAGER 84P672
Field
Description
Bytes in Buffer
The Bytes in Buffer[15:0] bits indicate the number of bytes
actually used in the current RPD's data buffer to store
packet data. The count excludes the 'dummy' bytes
inserted as a result of a non-zero Offset field. A count
greater than 32767 bytes indicates a packet that is
shorter than the expected length of the FCS field.
[15:0]
The Bytes in Buffer field is invalid when Status[0] or
Status[4] is asserted .
Next RPD Pointer
[14:0]
The Next RPD Pointer[14:0] bits store a RPDR which
enables the RMAC672 to support linked lists of RPDs.
This field, which is only valid when CE is equal to logic
zero, contains the RPDR to the next RPD in a linked list.
The RMAC672 links RPDs when more than one buffer is
needed to store a packet.
The Next RPD Pointer is not valid for the last RPD in a
linked list (when CE=1). When a packet requires only one
RPD, the Next RPD Pointer field is not valid.
RCC[9:0]
The Receive Channel Code (RCC[9:0]) bits are used by
the RMAC672 to associate a RPD with a channel.
For a linked list of RPDs, all the RPDs’ RCC[9:0] fields
are valid. i.e. all contain the same channel value.
Receive Buffer Size The Receive Buffer Size[15:0] bits indicate the size in
[15:0]
bytes of the current RPD's data buffer. This field is
expected to be configured by the Host during initialisation.
The Receive Buffer Size must be a non-zero integer
multiple of sixteen and less than or equal to 32752.
The Receive Buffer Size field is valid in all RPDs.
The Receive Buffer Size and Data Buffer Start Address fields are written only by
the host. The RMAC672 reads these fields to determine where to store packet
data. All other fields are written only by the RMAC672.
Receive Packet Descriptor Table
The Receive Packet Descriptor Table resides in host memory and stores all the
RPDs. The RPD Table can contain a maximum of 32768 RPDs. The base of
the RPD table is user programmable using the Rx Packet Descriptor Table Base
(RPDTB) register. The table is indexed by a Receive Packet Descriptor
Reference (RPDR) which is a 15-bit pointer defining the offset of a RPD from the
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44
PMC [ PMC-SIERRA, INC ]
