DP83934AVQB National Semiconductor, DP83934AVQB Datasheet - Page 27
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DP83934AVQB
Manufacturer Part Number
DP83934AVQB
Description
IC CTRLR ORIENT NETWORK 160PLCC
Manufacturer
National Semiconductor
Datasheet
1.DP83934AVQB.pdf
(104 pages)
Specifications of DP83934AVQB
Controller Type
Network Interface Controller (NIC)
Interface
Twisted Pair
Voltage - Supply
4.75 V ~ 5.25 V
Current - Supply
140mA
Operating Temperature
0°C ~ 70°C
Mounting Type
Surface Mount
Package / Case
160-MQFP, 160-PQFP
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
Other names
*DP83934AVQB
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5 0 Buffer Management
5 4 2 Receive Buffer Area (RBA)
The SONIC-T stores the actual data of a received packet in
the RBA The RBAs are designated by the Resource De-
scriptors in the RRA as described above The RXrsrc buff
wc0 1 fields of the RRA indicate the length of the RBA
When the SONIC-T gets an RBA from the RRA the
RXrsrc buff wc0 1 values are loaded into the Remaining
Buffer Word Count registers (RBWC0 1) These registers
keep track of how much space (in words) is left in the buffer
When a packet is buffered in a RBA it is buffered contigu-
ously (the SONIC-T will not scatter a packet into multiple
buffers or fragments) Therefore if there is not enough
space left in a RBA after buffering a packet to buffer at least
one more maximum sized packet (the maximum legal sized
packet expected to be received from the network) a new
buffer must be acquired The End of Buffer Count (EOBC)
register is used to tell the SONIC-T the maximum packet
size that the SONIC-T will need to buffer
5 4 2 1 End of Buffer Count (EOBC)
The EOBC is a boundary in the RBA based from the bottom
of the buffer The value written into the EOBC is the maxi-
mum expected size (in words) of the network packet that
the SONIC-T will have to buffer This word count creates a
line in the RBA that when crossed causes the SONIC-T to
fetch a new RBA resource from the RRA
Case
Case
Case
(RBWC0 1
1 SONIC-T buffers next packet in same RBA
2 SONIC-T detects an exhausted RBA and will buffer the next packet in another RBA
1
(Continued)
FIGURE 5-4 Receive Resource Area Format
t
EOBC)
FIGURE 5-5 Receive Buffer Area
27
Case
(RBWC0 1
Figure 5-5 illustrates the SONIC-T’s actions for (1)
Note The EOBC is a word count not a byte count Also the value pro-
5 4 2 2 Buffering the Last Packet in an RBA
At the start of reception the SONIC-T stores the packet
beginning at the Current Receive Buffer Address (CRBA0 1)
and continues until the reception is complete Concurrent
with reception the SONIC-T decrements the Remaining
Buffer Word Count (RBWC0 1) by one in 16-bit mode or by
two in 32-bit mode At the end of reception if the packet has
crossed the EOBC boundary the SONIC-T knows that the
next packet might not fit in the RBA This check is done by
comparing the RBWC0 1 registers with the EOBC If
RBWC0 1 is less than the EOBC (the last packet buffered
has crossed the EOBC boundary) the SONIC-T fetches the
next resource descriptor in the RRA If RBWC0 1 is greater
than or equal to the EOBC (the EOBC boundary has not
been crossed) the next packet reception continues at the
present location pointed to by CRBA0 1 in the same RBA
RBWC0 1
tion 5 4 4 4 for specific information about setting the EOBC
Note It is important that the EOBC boundary be ‘‘crossed ’’ In other words
grammed into EOBC must be a double word (32-bit) quantity when
the SONIC-T is in 32-bit mode (e g in 32-bit mode EOBC should be
set to 760 words not 759 words even though the maximum size of an
IEEE 802 3 packet is 759 words for double work boundary align-
ment)
case
occurs without case
buffer The result of this will be a buffer overflow (RBAE in the Inter-
rupt Status Register Section 6 3 6)
2
k
EOBC will not work properly and the SONIC-T will not fetch a new
k
EOBC)
t
1 in Figure 5-5 must exist before case
EOBC and (2) RBWC0 1
1 having occurred first the test for RBWC0 1
TL F 11719– 18
k
TL F 11719– 17
EOBC See Sec-
2 exists If case
2