
XRT7245
DS3 UNI FOR ATM
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PRELIMINARY
REV. 1.03
154
This section presents a detailed description of the
Transmit UTOPIA Interface block operating in the
“Single-PHY” mode. A description of the Receive
UTOPIA Interface block operating in the “Single-PHY”
mode is presented in Section 7.4.2.2.2.1. Whenever
the ATM Layer Processor wishes to write one or a se-
ries of ATM cells to the Transmit UTOPIA Interface
block, it must do the following.
Check the level of the TxClav output pin.
If the TxClav pin is “high” then there is available
space in the Tx FIFO for more ATM cell data and the
ATM Layer Processor may begin writing cell data to
the Transmit UTOPIA Interface block. However, if the
TxClav pin is “l(fā)ow”, then the Tx FIFO is too full to ac-
cept anymore data and the ATM Layer Processor
must wait until TxClav toggles “high” before writing
any cell data to the Transmit UTOPIA Interface block.
1.
Note:
The actual meaning of TxClav toggling “l(fā)ow”
depends upon whether the UNI is operating in the “Cell
Level” or “Octet Level” handshake modes.
Apply the first byte (or word) of the new cell to the
Transmit UTOPIA Data Bus.
The ATM Layer processor must designate this byte
(or word) as the beginning of a new cell, by pulsing
the TxSoC pin “high” for one clock period of TxClk.
2.
3.
Apply the Odd-Parity value of this first byte (or
word), currently residing on the Transmit UTOPIA
Data Bus, to the TxPrty input pin.
This should be done concurrently with pulsing the Tx-
SoC input pin “high”.
Assert the “Transmit UTOPIA Data Bus”—Write
Enable Signal, TxEnb*.
This step should also be done concurrently with pulsing
the TxSoC input pin “high”.
When writing the subsequent bytes (word) of the cell,
the ATM Layer Processor must repeatedly exercise
Steps 3 and 4, of the above list.
If the UNI is operating in the Octet-Level handshake
mode, then the ATM Layer processor should check
the level of the TxClav signal, at least once for every
four (4) writes of ATM cell data to the Transmit UTOPIA
Interface block.
If the UNI is operating in the Cell-Level Handshake
mode, then the ATM Layer Processor should check
the level of the TxClav signal, as it nears completion
of writing in a given cell.
The above-mentioned procedure is also depicted in
Flow-Chart Form in Figure 36; and in Timing Diagram
form in Figure 37 and 38.
4.
F
IGURE
35. S
IMPLE
I
LLUSTRATION
OF
S
INGLE
-PHY O
PERATION
DS3 UNI
ATM Switch
(ATM Layer Device)
TxData[15:0]
TxClav
TxSoC
TxEnB*
TxPrty
RxData[15:0]
RxClav
RxSoC
RxEnB*
RxPrty
TxPOS
TxNEG
TxLineClk
RxPOS
RxNEG
RxLineClk
Tx Flow Control Input
Tx Start of Cell Output
Tx Write Enable Output
Tx Utopia Data Bus Parity
Tx FIFO Clock Signal
To/From
DS3 LIU
TxClk
RxClk
Rx Flow Control Input
Rx Start of Cell Input
Rx Read Output Enable Signal
Rx Utopia Data Bus Parity
Rx FIFO Clock Signal
Rx ATM Cell Data
Tx ATM Cell Data