DP83905AVQB National Semiconductor, DP83905AVQB Datasheet - Page 54

• Manufacturer Part Number: DP83905AVQB
• Description: IC CONTROLR AT/LAN TP IN 160PQFP
• Manufacturer: National Semiconductor
• Series: AT/LANTIC™r

Specifications of DP83905AVQB

• Controller Type: AT, LAN Twisted-Pair Interface Controller
• Voltage - Supply: 4.75 V ~ 5.25 V
• Current - Supply: 100mA
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 160-BFQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Interface: -
• Other names: *DP83905AVQB

6 0 Operation of AT LANTIC Controller
INTERLEAVED LOCAL REMOTE OPERATION
When in I O mode the remote DMA is used to transfer data
to from the main system If a remote DMA transfer is initiat-
ed or in progress when a packet is being received or trans-
mitted the Remote DMA transfers will be interrupted for
higher priority Local DMA transfers When the Local DMA
transfer is completed the Remote DMA will rearbitrate for
the bus and continue its transfers
If the FIFO requires service while a remote DMA is in prog-
ress the Local DMA burst is appended to the Remote Trans-
fer When switching from a local transfer to a remote trans-
fer there is a break to allow the CPU to fairly contend for the
bus
REMOTE DMA BI-DIRECTIONAL PORT
The Remote DMA transfers data between the local buffer
memory and the internal bidirectional port (memory to I O
transfer)
This transfer is arbitrated on a transfer by transfer basis
versus the burst transfer mode used for Local DMA trans-
fers This bidirectional port is integrated onto the AT LAN-
TIC Controller and is read written by the host All transfers
through this port are asynchronous At any one time trans-
fers are limited to one direction either from the port to local
buffer memory (Remote Write) or from local buffer memory
to the port (Remote Read)
FIGURE 38 I O Operation All Data Transfers and
Arbitration is Controlled by the NIC Core
FIGURE 39 1st Received Packet
Removed by Remote DMA
TL F 11498–35
TL F 11498–36
54
(Continued)
I O MODE REMOVING PACKETS FROM RING
Network activity is isolated on a local bus where the
AT LANTIC Controller’s local DMA channel performs burst
transfers between the buffer memory and the AT LANTIC
Controller’s FIFO The Remote DMA transfers data be-
tween the buffer memory and the host memory via the inter-
nal bidirectional I O port The Remote DMA provides local
addressing capability and is used as a slave DMA by the
host The host system reads the I O port to transfer data
between the system and I O port The AT LANTIC Control-
ler allows Local and Remote DMA operations to be inter-
leaved
Packets are removed from the ring using the Remote DMA
When using the Remote DMA the Send Packet command
can be used This programs the Remote DMA to automati-
cally remove the received packet pointed to by the Bounda-
ry Pointer At the end of the transfer the AT LANTIC Con-
troller moves the Boundary Pointer freeing additional buff-
ers for reception The Boundary Pointer can also be moved
manually by programming the Boundary Register Care
should be taken to keep the Boundary Pointer at least one
buffer behind the Current Page Pointer
Data transfer by the Remote DMA to the integrated I O data
port is dependent on whether the AT LANTIC Controller is
set into 8-bit mode or 16-bit mode In 8-bit mode all trans-
fers are 8 bits (1 byte) wide When in 16-bit mode all trans-
fers are 16 bits (1 word) wide The data width is selected by
setting the WTS bit in the Data Configuration Register and
setting the DWID pin for the proper mode
The following is a suggested method for maintaining the
Receive Buffer Ring pointers if in shared memory mode or if
remote read is used in I O mode
1 At initialization set up a software variable (next pkt) to
2 When initializing the AT LANTIC Controller set
3 After a packet is DMAed from the Receive Buffer Ring
Note the size of the Receive Buffer Ring is reduced by one
256 byte buffer this will not however impede the operation
of the AT LANTIC Controller The advantage of this
scheme is that it easily differentiates between buffer full and
buffer empty it is full if BNDRY
BNDRY
to empty the buffer ring this scheme cannot be used
BNDRY must be initialized equal to CURR or the first exe-
cuted send packet will not return data from the received
packet which will be written at CURR The Overwrite Warn-
ing bit of the Interrupt Status Register must be used in this
mode to differentiate between buffer full and buffer empty
indicate where the next packet will be read At the begin-
ning of each Remote Read DMA operation the value of
next pkt will be loaded into RSAR0 and RSAR1
BNDRY
CURR
next pkt
the Next Page Pointer (second byte in the AT LANTIC
Controller buffer header is used to update BNDRY and
next pkt
next pkt
BNDRY
If BNDRY
e
e
e
e
CURR
PSTART
PSTART
e
e
k
Next Page Pointer
PSTART
Next Page Pointer
PSTART then BNDRY
b
1 If in I O mode send packet is used
a
1
a
1
b
e
1
CURR empty when
e
PSTOP
b
1