DP83932CVF25 National Semiconductor, DP83932CVF25 Datasheet - Page 13

• Manufacturer Part Number: DP83932CVF25
• Manufacturer: National Semiconductor

Specifications of DP83932CVF25

• Operating Supply Voltage (typ): 5V
• Operating Supply Voltage (min): 4.75V
• Operating Supply Voltage (max): 5.25V
• Mounting: Surface Mount
• Pin Count: 132
• Lead Free Status / RoHS Status: Not Compliant

3 0 Buffer Management
3 1 BUFFER MANAGEMENT OVERVIEW
The SONIC’s buffer management scheme is based on sep-
arate buffers and descriptors ( Figures 3-2 and 3-11 ) Pack-
ets that are received or transmitted are placed in buffers
called the Receive Buffer Area (RBA) and the Transmit Buff-
er Area (TBA) The system keeps track of packets in these
buffers using the information in the Receive Descriptor Area
(RDA) and the Transmit Descriptor Area (TDA) A single
(TDA) points to a single TBA but multiple RDAs can point to
a single RBA (one RDA per packet in the buffer) The Re-
ceive Resource Area (RRA) which is another form of de-
scriptor is used to keep track of the actual buffer
When packets are transmitted the system sets up the pack-
ets in one or more TBAs with a TDA pointing to each TBA
There can only be one packet per TBA TDA pair A single
TBA however may be made up of several fragments of
data dispersed in memory There is one TDA pointing to
each TBA which specifies information about the buffer’s
size location in memory number of fragments and status
after transmission The TDAs are linked together in a linked
list The system causes the SONIC to transmit the packets
by passing the first TDA to the SONIC and issuing the trans-
mit command
Before a packet can be received an RDA and RBA must be
set up by the system RDA’s are made up as a linked list
similar to TDAs An RDA is not linked to a particular RBA
though Instead an RDA is linked specifically to a packet
after it has been buffered into an RBA More than one pack-
et can be buffered into the same RBA but each packet gets
its own RDA A received packet can not be scattered into
fragments The system only needs to tell the SONIC where
the first RDA and where the RBAs are Since an RDA never
specifically points to an RBA the RRA is used to keep track
of the RBAs The RRA is a circular queue of pointers and
buffer sizes (not a linked list) When the SONIC receives a
packet it is buffered into a RBA with a corresponding and
unique RDA that is written to so that it points to and de-
scribes the new packet If the RBA does not have enough
space to buffer the next packet a new RBA is obtained from
the RRA
3 2 DESCRIPTOR AREAS
Descriptors are the basis of the buffer management scheme
used by the SONIC A RDA points to a received packet
within a RBA RRA points to a RBA and a TDA points to a
TBA which contains a packet to be transmitted The con-
ventions and registers used to describe these descriptors
are discussed in the next three sections
3 2 1 Naming Convention for Descriptors
The fields which make up the descriptors are named in a
consistent manner to assist in remembering the usage of
each descriptor Each descriptor name consists of three
components in the following format
The first two capital letters indicate whether the descriptor is
used for transmission (TX) or reception (RX) and is then
followed by the descriptor name having one of two names
RX TX descriptor name field
13
Figure 3-1 shows an example of the Transmit Descriptor
rsrc
pkt
The last component consists of a field name to distinguish it
from the other fields of a descriptor The field name is sepa-
rated from the descriptor name by a period (‘‘ ’’) An exam-
ple of a descriptor is shown below
3 2 2 Abbreviations
The abbreviations in Table 3 1 are used to describe the
SONIC registers and data structures in memory The ‘‘0’’
and ‘‘1’’ in the abbreviations indicate the least and most
significant portions of the registers or descriptors Table 3-1
lists the naming convention abbreviations for descriptors
3 2 3 Buffer Management Base Addresses
The SONIC uses three areas in memory to store descriptor
information the Transmit Descriptor Area (TDA) Receive
Descriptor Area (RDA) and the Receive Resource Area
(RRA) The SONIC accesses these areas by concatenating
a 16-bit base address register with a 16-bit offset register
The base address register supplies a fixed upper 16 bits of
address and the offset registers provide the lower 16 bits of
address The base address registers are the Upper Trans-
mit Descriptor Address (UTDA) Upper Receive Descriptor
Address (URDA) and the Upper Receive Resource Address
(URRA) registers The corresponding offset registers are
shown below
See Table 3-1 for definition of register mnemonics
Area and the Receive Descriptor Area being located by the
UTDA and URDA registers The descriptor areas RDA
TDA and RRA are allowed to have the same base address
i e URRA
to prevent these areas from overwriting each other
Upper Address Registers
e
e
Resource descriptor
Packet descriptor
e
URRA
URDA
UTDA
URDA
e
UTDA Care however must be taken
RSA REA RWP RRP
Offset Registers
CRDA
CTDA
TL F 10492 – 86