DP83932CVF25 National Semiconductor, DP83932CVF25 Datasheet - Page 19

• 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
and the buffer size to 762 words (1524 bytes) A similar
example for 16-bit mode would be EOBC
(1518 bytes) and the buffer size set to 760 words (1520
bytes) The buffer can be any size but as long as the EOBC
is 2 words for 32-bit mode or 1 word for 16-bit mode less
than the buffer size only one packet will be buffered in that
RBA
Note 1 It is possible to filter out most oversized packets by setting the buff-
Note 2 When buffering one packet per buffer it is suggested that the val-
3 4 5 Beginning Of Reception
At the beginning of reception the SONIC checks its inter-
nally stored EOL bit from the previous RXpkt link field for a
‘‘1’’ If the SONIC finds EOL
previous reception there were no more remaining receive
packet descriptors It re-reads the same RXpkt link field to
check if the system has updated this field since the last
reception If the SONIC still finds EOL
es (See Section 3 5 for adding descriptors to the list ) Oth-
erwise the SONIC begins storing the packet in the RBA
starting at the Current Receive Buffer Address (CRBA0 1)
registers and continues until the packet has completed
Concurrent with the packet reception the Remaining Buffer
Word Count (RBWC0 1) registers are decremented after
each word is written to memory This register determines
the remaining words in the RBA at the end of reception
3 4 6 End Of Packet Processing
At the end of a reception the SONIC enters its end of pack-
et processing sequence to determine whether to accept or
reject the packet based on receive errors and packet size
At the end of reception the SONIC enters one of the follow-
ing two sequences
Successful reception sequence
Buffer recovery for runt packets or packets with errors
er size to 760 words (1520 bytes) in 32-bit mode or 759 words (1518
bytes) in 16-bit mode EOBC would be set to 758 words (1516
bytes) for both cases With this configuration any packet over 1520
bytes in 32-bit mode or 1518 bytes in 16-bit mode will not be
completely buffered because the packet will overflow the buffer
When a packet overflow occurs a Receive Buffer Area Exceeded
interrupt (RBAE in the Interrupt Status Register Section 4 3 6) will
occur
ues in Note 1 above be used Since the minimum legal sized Ether-
net packet is 64 bytes however it is possible to set EOBC as much
as 64 bytes less than the buffer size and still end up with one packet
per buffer Figure 3-10 shows this ‘‘range ’’
e
1 it recognizes that after the
FIGURE 3-10 Setting EOBC for Single Packet RBA
e
Range of EOBC
(Continued)
1 reception ceas-
e
759 words
e
(RXrsrc wc0 1
19
b
3 4 6 1 Successful Reception
If the SONIC accepts the packet it first writes 5 words of
descriptor information in the RDA beginning at the address
pointed to by the Current Receive Descriptor Address
(CRDA) register It then reads the RXpkt link field to ad-
vance the CRDA register to the next receive descriptor The
SONIC also checks the EOL bit for a ‘‘1’’ in this field If
EOL
The SONIC recovers the address of the current RXpkt link
field (from a temporary register) and generates a ‘‘Receive
Descriptors Exhausted’’ indication in the Interrupt Status
register (See Section 3 4 7 on how to add descriptors ) The
SONIC maintains ownership of the descriptor by not writing
to the RXpkt in use field Otherwise if EOL
advances the CRDA register to the next descriptor and re-
sets the RXpkt in use field to all ‘‘0’s’’
The SONIC accesses the complete 7 word RDA descriptor
in a single block operation
The SONIC also checks if there is remaining space in the
RBA The SONIC compares the Remaining Buffer Word
Count (RBWC0 1) registers with the static End Of Buffer
Count (EOBC) If the RBWC is less than the EOBC a maxi-
mum sized packet will no longer fit in the remaining space in
the RBA hence the SONIC fetches a resource descriptor
from the RRA and loads its registers with the pointer and
word count of the next available RBA
3 4 6 2 Buffer Recovery For Runt Packets Or
Packets With Errors
If a runt packet (less than 64 bytes) or packet with errors
arrives and the Receive Control register has been config-
ured to not accept these packets the SONIC recovers its
pointers back to the original positions The CRBA0 1 regis-
ters are not advanced and the RBWC0 1 registers are not
decremented The SONIC recovers its pointers by maintain-
ing a copy of the buffer address in the Temporary Receive
Buffer Address registers (TRBA0 1) The SONIC recovers
the value in the RBWC0 1 registers from the Temporary
Buffer Word Count registers (TBWC0 1)
3 4 7 Overflow Conditions
When an overflow condition occurs the SONIC halts its
DMA operations to prevent writing into unauthorized memo-
ry The SONIC uses the Interrupt Status register (ISR) to
indicate three possible overflow conditions that can occur
2 to RXrsrc wc0 1
e
1 no more descriptors are available for the SONIC
b
32)
TL F 10492 – 17
e
0 the SONIC