DP83907 datasheet(51/70 Pages) NSC

51 / 70 page

60 Operation of DP83907 (Continued)

The idle state is exited and the DP83907 will drive the local

memory bus when a request from the FIFO in the DP8390

(NIC) core causes the memory bus interface logic to issue a

read or write operation such as when the DP83907 is trans-

mitting or receiving data

The NIC Core’s Remote DMA also requests access from

the memory bus When software programs an IO data

transfer between the CPU and the buffer RAM the Remote

DMA controls this request

All Local DMA transfers are burst transfers the DMA will

transfer an exact burst of bytes programmed in the Data

Configuration Register (DCR) then relinquish the memory

bus If there are remaining bytes in the FIFO the next burst

will not be initiated until the FIFO threshold is exceeded

IO Mode Operation

In IO mode the DP83907 transfers data to and from the

packet buffer RAM by utilizing the Remote DMA logic which

is programmed by the main system CPU to transfer data

through the DP83907’s internal data

TLF12082 – 33

FIGURE 38 IO Operation All Data Transfers and

Arbitration is Controlled by the NIC Core

INTERLEAVED LOCALREMOTE OPERATION

When in IO mode the remote DMA is used to transfer data

tofrom 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 bi-directional port (memory to IO

transfer)

This transfer is arbitrated on a transfer by transfer basis

versus the burst transfer mode used for Local DMA trans-

fers This bi-directional port is integrated onto the DP83907

and is readwritten by the host All transfers through this

port are asynchronous At any one time transfers are limited

to one direction either form the port to local buffer memory

(Remote Write) or form local buffer memory to the port (Re-

mote Read)

TLF12082 – 34

FIGURE 39 1st Received Packet Removed

by Remote DMA

IO MODE REMOVING PACKETS FROM RING

Network activity is isolated on a local bus where the

DP83907’s local DMA channel performs burst transfers be-

tween the buffer memory and the DP83907’s FIFO The Re-

mote DMA transfers data between the buffer memory and

the host memory via the internal bi-directional IO port The

Remote DMA provides local addressing capability and is

used as a slave DMA by the host The host system reads

the IO port to transfer data between the system and IO

port The DP83907 allows Local and Remote DMA opera-

tions to be interIeaved

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 DP83907 moves

the Boundary Pointer freeing additional buffers for recep-

tion 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 IO data

port is dependent on whether the DP83907 is set into 8 bit

mode or 16 bit mode In 8 bit mode all transfers are 8 bits (1

byte) wide When in 16 bit mode all transfers 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

1 At initialization set up a software variable (next

pkt) to

indicate where the next packet will be read At the begin-

ning of each Remote Read DMA operation the value of

pkt will be loaded into RSAR0 and RSAR1

2 When initializing the DP83907 Controller set

BNDRY e PSTART

CURR e PSTART a 1

pkt e PSTART a 1

3 After a packet is DMAed from the Receive Buffer Ring

the Next Page Pointer (second byte in the DP83907 Con-

troller buffer header is used to update BNDRY and

pkt

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