cx28250 Mindspeed Technologies, cx28250 Datasheet - Page 75

• Manufacturer Part Number: cx28250
• Description: Cx28250 Atm Physical Interface Phy Devices
• Manufacturer: Mindspeed Technologies

CX28250
ATM Physical Interface (PHY) Devices
2.5.5 Handshaking
Table 2-18. UTOP1 Register, Bits [1:0]
28250-DSH-002-C
Bit
1
0
Default
0
0
TxFill[1]
TxFill[0]
The CX28250 provides both cell-level and octet-level handshaking on its
UTOPIA interface (only cell-level is used in Level 2). The primary distinction
between these two levels is the amount of data that is sent or received. Octet-level
sends and receives four octets at a time, while cell-level sends and receives a full
cell at a time, depending on FIFO size and availability. In octet-level
handshaking, UTxClAv is an active low, FIFO full indicator. In cell-level, it is an
active high, cell buffer available indicator. These two options are selectable in the
Handshake bit, bit 4, of the UTOP1 register (0x0A).
designed to provide a 'look ahead' feature to allow the ATM layer to anticipate
when the FIFOs will be full. The UTOPIA layer polls the port to determine if that
port has room for a cell. In response, the port asserts (logic 1), the TxClAv line if
it has room and de-asserts (0) the line if it does not have room. The threshold is
controlled by bits [1:0] in the UTOP1 register as listed in
maximum performance when using a standard ATM layer device, Mindspeed
recommends leaving these set to 00.
Name
TxClAv (transmit cell available): The CX28250 implementation of TxClAv is
Mindspeed Technologies
These bits set the Transmit FIFO Fill Level threshold for UTxClAv pin.
00—The TxClAv line will be asserted if the UTOPIA FIFO can accept at least 1
more complete cell.
01—The TxClAv line will be asserted only if the UTOPIA FIFO has room for
least 2 more cells.
10—The TxClAv line will be asserted only if the UTOPIA FIFO has room for at
least 3 more cells.
11—The TxClAv line will be asserted only if the UTOPIA FIFO can accept at
least 3 more cells.
™
Description
2.0 Functional Description
Table
2.5 UTOPIA Interface
2-18. For
2-39