DP83907 datasheet(52/70 Pages) NSC

52 / 70 page

60 Operation of DP83907 (Continued)

TLF12082 – 35

FIGURE 40 Remote DMA Auto Initialization from Buffer Ring

pkt e Next Page Pointer

BNDRY e Next Page Pointer b 1

If BNDRY k PSTART then BNDRY e PSTOP b 1

Note the size of the Receive Buffer Ring is reduced by one

256-byte buffer this will not however impede the operation

of the DP83907 The advantage of this scheme is that it

easily differentiates between buffer full and buffer empty it

is full if BNDRY e CURR empty when BNDRY e CURR-1

If in IO mode send packet is used to empty the buffer ring

this scheme cannot be used BNDRY must be initialized

equal to CURR or the first executed send packet will not

return data from the received packet which will be written at

CURR The Overwrite Warning bit of the Interrupt Status

buffer full and buffer empty

IO REMOTE DMA COMMANDS

The Remote DMA channel is used in the IO Mode to both

assemble packets for transmission and to remove received

packets from the Receive Buffer Ring It may also be used

for moving blocks of data or commands between host mem-

ory and local buffer memory (In Shared Memory Mode the

Remote DMA should be disabled and not used Packet

transfer tofrom the system is accomplished by normal CPU

readwrite operations)

There are three modes of Remote DMA operation Remote

Write Remote Read or Send Packet

Two register pairs are used to control the Remote DMA a

Remote Start Address (RSAR0 RSAR1) and a Remote

Byte Count (RBCRO RBCR1) register pair The Start Ad-

dress Register pair points to the beginning of the block to be

moved while the Byte Count Register pair is used to indicate

the number of bytes to be transferred Full handshake logic

is provided to move data between local buffer memory and

a bi-directional IO port

Remote Write

A Remote Write transfer is used to move a

block of data from the host into local buffer memory The

Remote DMA will read data from the IO port and sequen-

tially write it to local buffer memory beginning at the Remote

Start Address The DMA Address will be incremented and

the Byte Counter will be decremented after each transfer

The DMA is terminated when the Remote Byte Count Regis-

ter reaches a count of zero

Remote Read

A Remote Read transfer is used to move a

block of data from local buffer memory to the host The

Remote DMA will sequentially read data from the local buff-

er memory beginning at the Remote Start Address and

write data to the IO port

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