
PM7346 S/UNI-QJET
DATASHEET
PMC-960835
ISSUE 6
SATURN QUAD USER NETWORK INTERFACE FOR J2, E3, T3
PMC-SIERRA, INC. PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA INC., AND ITS CUSTOMERS’ INTERNAL USE
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9.20 TXFF Transmit FIFO
The Transmit FIFO (TXFF) provides FIFO management and the S/UNI-QJET
transmit cell interface. The transmit FIFO contains four cells. The FIFO depth
may be programmed to four, three, two, or one cells. The FIFO provides the cell
rate decoupling function between the transmission system physical layer and the
ATM layer.
In general, the management functions include emptying cells from the transmit
FIFO, indicating when the transmit FIFO is full, maintaining the transmit FIFO
read and write pointers and detecting a FIFO overrun condition.
The FIFO interface is “UTOPIA Level 2” compliant and accepts a write clock
(TFCLK), a write enable signal (TENB), the start of a cell (TSOC) indication, and
the parity bit (TPRTY), and the ATM device address (TADR[4:0]) when data is
written to the transmit FIFO (using the rising edges of TFCLK). The interface
provides the transmit cell available status (TCA and DTCA[4:1]) which can
transition from "available" to "unavailable" when the transmit FIFO is near full
(when TCALEVEL0 is logic 0) or when the FIFO is full (when TCALEVEL0 is
logic 1) and can accept no more writes. To reduce FIFO latency, the FIFO depth
at which TCA and DTCA[x] indicates "full" can be set to one, two, three or four
cells by the FIFODP[1:0] bits of TXCP-50 Configuration 2 register. If the
programmed depth is less than four, more than one cell may be written after TCA
or DTCA[x] is asserted as the TXCP-50 still allows four cells to be stored in its
FIFO. This interface also indicates FIFO overruns via a maskable interrupt and
register bit, but write accesses while TCA or DTCA[x] is logic 0 are not
processed. The TXFF automatically transmits idle cells until a full cell is available
to be transmitted.
9.21 TTB Trail Trace Buffer
The Trail Trace Buffer (TTB) extracts and sources the trail trace message carried
in the TR byte of the G.832 E3 stream. The message is used by the OS to
prevent delivery of traffic from the wrong source and is 16 bytes in length. The
16-byte message is framed by the PTI Multiframe Alignment Signal (TMFAS =
'b10000000 00000000). One bit of the TMFAS is placed in the most significant
bit of each message byte. In the receive direction, the trail trace message is
extracted from the serial overhead stream output by the E3-FRMR. The
extracted message is stored in the internal RAM for review by an external
microprocessor. By default, the TTB will write the byte of a 16-byte message with
its most significant bit set high to the first location in the RAM. The extracted trail
trace message is checked for consistency between consecutive multiframes. A
message received unchanged three or five times (programmable) is accepted for