TNETA1570 Datasheet, PDF (32/68 Pages) Texas Instruments – ATM SEGMENTATION AND REASSEMBLY DEVICE WITH INTEGRATED 64-BIT PCI-HOST INTERFACE

TNETA1570
ATM SEGMENTATION AND REASSEMBLY DEVICE
WITH INTEGRATED 64ĆBIT PCIĆHOST INTERFACE
SDNS033B − JUNE 1995 − REVISED MAY 1996
PRINCIPLES OF OPERATION
RDY (bit 31)
This bit indicates whether the buffer is ready for segmentation. The host sets this bit to a one to indicate that
the buffer is ready to be transmitted. The TNETA1570 does not write to this bit.
The RDY bits of the buffers within a packet, which has a cell divided across multiple buffers, is set in a zipper-up
fashion, (i.e. the RDY bit of the last buffer in the chain is set first). If the last cell in the buffer has its beginning
in one buffer and the ending in another, the RDY bit for the first buffer cannot be set before the RDY bit for the
second buffer is set. This propagates down the buffer chain until a cell is completed on an even buffer boundary.
start of packet (SOP) (bit 30)
This bit is set by the host indicating that this is the first buffer of a packet that consists of one or more buffers.
This bit is also set if a packet consists of only a single buffer.
end of packet (EOP) (bit 29)
This bit is set by the host to indicate that this is the last buffer of a packet. If a packet consists of only one buffer,
both the SOP and EOP bits are set. If a packet consists of multiple buffers, the SOP bit is set on the first buffer
and the EOP bit is set on the last buffer.
abort (bit 28)
When this bit is set by the host, the TNETA1570 stops segmentation of the packet and performs EOP processing
immediately. An entry is written into the transmit completion ring indicating that an abort has occurred. When
an abort occurs, the AAL5-length field in the AAL5 trailer of the last cell transmitted is set to zero to indicate that
an abort has occurred.
transmit AAL-packet-type indicator (bits 27 and 26)
These bits are set by the host to indicate the AAL type of the packet being transmitted. Three options are
available for processing a packet for transmission as shown in the following table.
BIT 27
0
0
1
1
BIT 26
0
1
0
1
INDICATION
Transparent-AAL packet with PTI bits set to indicate EOP
AAL5
Transparent-AAL packet without PTI bits set to indicate EOP
Invalid
AAL5 processing includes the calculation of the 32-bit CRC and the addition of the pad, control, and length fields.
All buffers associated with an AAL5 packet must have the AAL5-indication bits set. When either of the other two
processing methods is chosen, the TNETA1570 does not perform packet-level processing except for adding
the necessary pad to complete a 48-byte payload. If both bits 27 and 26 are set to zero, the device also sets
the PTI field in the last cell of a packet to a value of 0 x 1 to indicate EOP. If bits 27 and 26 are set to a value
of 10, the PTI field in the last cell of the packet is not modified. This last method can be used to send VC-level
OAM cells, which requires that the PTI value of the cell being transmitted be set to a value of 10x. The
TNETA1570 does not modify the PTI field for these cells.
transmit completion-ring select (bit 25)
This bit is set by the host to indicate whether the TNETA1570 uses the transmit completion ring with or without
interrupt when a buffer completes segmentation. If this bit is set to a one, the TNETA1570 uses the completion
ring with interrupt. If this bit is cleared, the TNETA1570 uses the completion ring without interrupt.
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