XTNETA1622DW datasheet(44/68 Pages) TI1

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TNETA1570

ATM SEGMENTATION AND REASSEMBLY DEVICE

WITH INTEGRATED 64BIT PCIHOST INTERFACE

SDNS033B − JUNE 1995 − REVISED MAY 1996

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

POST OFFICE BOX 1443

• HOUSTON, TEXAS 77251−1443

PRINCIPLES OF OPERATION

VALID (bit 31)

The VALID bit is set to 1, except when the start-of-packet pointer is not valid. This condition occurs if a cell is

received on a DMA channel that is in buffer starvation, (i.e., when reassembly has started and the first buffer

in a packet is not available.

start-of-packet pointer (bits 29 −0)

This word provides the location of the first data-buffer in the receive data-buffer chain. This word is copied

directly from word 4 of the RX DMA state table. Only the upper 30 bits of the 32-bit address are copied to this

entry.

word 3 (AAL5 trailer)

CPCS-UU (bits 31 − 24)

CPI (bits 23 − 16)

Length (bits 15 − 0)

AAL5 trailer (bits 31 −0)

The CPCS-UU field, the CPI field, and the length field from the AAL5 trailer of an incoming packet are copied

to this entry. This field is valid only in AAL5 mode.

word 4

Control (bits 31 − 30)

FIFO-Pointer/Ring-Descriptor Index (bits 29 − 0)

OWN (bit 31)

This bit is set to a one by the host to indicate that this entry is available for use by the TNETA1570. If the OWN

bit is not set when the TNETA1570 tries to access an entry, RX freeze occurs. The TNETA1570 clears this bit

to indicate that it has completed the entry and that the entry is ready for the host to evaluate.

error entry (bit 30)

This bit is set by the TNETA1570 when one or more of the error conditions indicated by bits 27−31 of word 1

occur.

FIFO-pointer/ring-descriptor index (bits 29 −0)

This field is copied from word 6 of the receive DMA state table. The value of this field is used by the host to

determine which ring/FIFO the ring is to be returned to when the buffers has been read.

word 5

Reserved (bits 31 − 0)

reserved (bits 31 −0)

This word is not used by the TNETA1570 and reserved for future revisions of the TNETA1570.

word 6

Reserved (bits 31 − 0)

reserved (bits 31 −0)

This word is not used by the TNETA1570 and reserved for future revisions of the TNETA1570.

word 7

Reserved (bits 31 − 0)

reserved (bits 31 −0)

This word is not used by the TNETA1570 and reserved for future revisions of the TNETA1570.

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