DP83916VF National Semiconductor, DP83916VF Datasheet - Page 19

• Manufacturer Part Number: DP83916VF
• Description: IC CTRLR ORIENT NETWK IN 132PQFP
• Manufacturer: National Semiconductor
• Series: SONIC™r

Specifications of DP83916VF

• Controller Type: Network Interface Controller (NIC)
• Interface: Bus
• Mounting Type: Surface Mount
• Package / Case: 132-MQFP, 132-PQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Current - Supply: -
• Voltage - Supply: -
• Operating Temperature: -
• Other names: *DP83916VF

3 0 Buffer Management
An example would be EOBC
the buffer size set to 760 words (1520 bytes) The buffer
can be any size but as long as the EOBC is 1 word 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-16 checks its in-
ternally stored EOL bit from the previous RXpkt link field for
a ‘‘1’’ If the SONIC-16 finds EOL
the previous reception there were no more remaining re-
ceive 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-16 still finds EOL
ceases (See Section 3 5 for adding descriptors to the list )
Otherwise the SONIC-16 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 Re-
maining Buffer Word Count (RBWC0 1) registers are decre-
mented 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-16 enters its end of
packet processing sequence to determine whether to ac-
cept or reject the packet based on receive errors and pack-
et size At the end of reception the SONIC-16 enters one of
the following two sequences
Successful reception sequence
Buffer recovery for runt packets or packets with errors
er size to 759 words (1518 bytes) EOBC would be set to 758 words
(1516 bytes) for both cases With this configuration any packet over
1518 bytes will not be completely buffered because the packet will
overflow the buffer When a packet overflow occurs a Receive Buff-
er 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
759 words (1518 bytes) and
e
1 it recognizes that after
FIGURE 3-10 Setting EOBC for Single Packet RBA
(Continued)
Range of EOBC
e
1 reception
e
(RXrsrc wc0 1
19
b
3 4 6 1 Successful Reception
If the SONIC-16 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-16 also checks the EOL bit for a ‘‘1’’ in this field If
EOL
16 The SONIC-16 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 descrip-
tors ) The SONIC-16 maintains ownership of the descriptor
by not writing to the RXpkt in use field Otherwise if
EOL
next descriptor and resets the RXpkt in use field to all
‘‘0’s’’
The SONIC-16 accesses the complete 7 word RDA descrip-
tor in a single block operation
The SONIC-16 also checks if there is remaining space in the
RBA The SONIC-16 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-16 fetches a resource descrip-
tor 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-16 recovers
its pointers back to the original positions The CRBA0 1 reg-
isters are not advanced and the RBWC0 1 registers are not
decremented The SONIC-16 recovers its pointers by main-
taining a copy of the buffer address in the Temporary Re-
ceive Buffer Address registers (TRBA0 1) The SONIC-16
recovers the value in the RBWC0 1 registers from the Tem-
porary Buffer Word Count registers (TBWC0 1)
3 4 7 Overflow Conditions
When an overflow condition occurs the SONIC-16 halts its
DMA operations to prevent writing into unauthorized memo-
ry The SONIC-16 uses the Interrupt Status register (ISR) to
indicate three possible overflow conditions that can occur
2 to RXrsrc wc0 1
e
e
1 no more descriptors are available for the SONIC-
0 the SONIC-16 advances the CRDA register to the
b
32)
TL F 11722 – 17