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LAN83C171

EPIC/XF ACPI/PC 97 Compliant Integrated PCI 10/100 Mbps Fast Ethernet Controller

SMSC -> Microchip 

Transmit Length field will not be overwritten.

If TXIAF is true in the last descriptor for the

frame, then the transmit complete (TXC)

interrupt will be set. When there are no

frames left in the queue and the last

transmission has completed on the network,

the transmit DMA will set the transmit chain

complete (TCC) interrupt and return to its idle

state.

Note: The difference between the TQE and the

TCC interrupt is that the TQE interrupt is set

only when there are no frames left in the

queue. The TCC interrupt is set only when

there are no frames left in the queue AND the

last frame in the transmit queue buffer has

transmitted. Hence the TQE interrupt is set

first and may or may not be followed by a TCC

interrupt.

Fragment List Method

Descriptor points to a fragment list.

This method of queuing a transmit frame is

much like the first method, except that each

frame is always specified by one descriptor

which points to a list of buffers (fragment list)

instead of the buffers themselves. The

FRAGLIST bit in the descriptor must be set to

1 and the LFFORM bit must properly indicate

the format of the fragment list. The first entry

in the fragment list tells how many data buffers

(fragments) are listed. Up to 63 fragments are

allowed. The remaining entries specify the

starting address and length of each buffer.

As in the direct queuing method, the transmit

DMA will copy fragments one at a time into the

local buffer until Transmit Length bytes have been

copied or all of the fragments have been read. If

early transmit is enabled, transmission will be

initiated when enough bytes have been copied to

meet the early transmit threshold. Otherwise

transmission will be initiated when the entire copy

is complete.

When more than one frame is queued, the

transmit DMA will begin copying a second frame

while the first is being transmitted. It will continue

copying fragments until the entire frame is loaded

or the first transmission has completed. If the

copy completes while the first transmission is still

in progress, the LAN83C171 will stop and wait.

When the transmission is finished, the

LAN83C171 will post the status into the first

descriptor and immediately initiate the second

transmission. If the transmission completes

before the copy is done, the LAN83C171 will

pause between fragments to post the status and

then resume the copy. If the early transmit

threshold has already been exceeded then the

second transmission will be initiated immediately.

Figure 3 shows a drawing of the Transmit Buffer

Structure.

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