TNETA1570 datasheet(38/68 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

word 1

Current-Buffer Pointer (bits 31 − 0)

The current-buffer pointer is set by the TNETA1570 to a value equal to the start-of-buffer pointer plus four 32-bit

words when reassembly of a new buffer begins. After that, the pointer is adjusted to point to the current-data

location after each payload-data transfer to the host.

word 2

Reserved

Start-of-Buffer Pointer (bits 29 − 0)

Word 2 is copied from word 0 of the RX free-buffer-ring entry or RX free-buffer FIFO entry.

word 3

Current Transparent-AAL Packet Counter (bits 31−16)

Current-Buffer Length (bits 15 − 0)

current transparent-AAL packet counter (bits 31 −16)

This field is copied from word 5 bit (bits15 −0) (see word 5 definition) when the first cell of a transparent-AAL

packet arrives. This field is decremented every time a cell arrives until its value is equal to zero. Once this field’s

value reaches zero, EOP processing for a transparent-AAL packet is initiated. This field is used only if the

receive DMA channel is configured to receive counter-based transparent-AAL packets (i.e., bit 27 of receive

DMA state table entry word 0 has been set to a one and bit 26 has been set to a zero).

current-buffer length (bits 15 −0)

This field is copied either from word 1 of the RX free-buffer ring-pointer table entry or FIFO free-buffer-size

every time a cell is received until it reaches zero. If the EOP cell has not arrived at that time, a new buffer is

fetched from the free-buffer ring or FIFO.

word 4

Reserved

Start-of-Buffer Pointer (bits 29 − 0)

Word 4 is copied from word 0 of the receive free-buffer ring-pointer-table entry for only the first buffer in each

new packet. When the received packet is complete, this value is written to the receive complete-ring-descriptor

entry,

word 5 (AAL5 packets)

Partial-AAL5-Receive CRC (bits 31 − 0)

This field is used by the TNETA1570 to save the interim results of the 32-bit CRC for AAL5 packets when the

receive DMA channel is configured to receive AAL5 packets.

transparent-AAL packets using counter-based reassembly

Reserved (bits 31 − 16)

Transparent-AAL Packet Length (bits 15 − 0) (counter base only)

transparent-AAL packet length (bits 15 −0)

This field contains the number of cells that constitute a transparent-AAL packet when the receive DMA channel

has been configured to receive transparent-AAL packets using counter-based reassembly. This field must be

initialized by the host at startup.

TNETA1570 数据表(PDF) 38 Page - Texas Instruments

TNETA1570 数据表(HTML) 38 Page - Texas Instruments

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