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PRELIMINARY
INVERSE MULTIPLEXING OVER ATM
PM7341 S/UNI-IMA-84
DATASHEET
PMC-2000223
ISSUE 4
INVERSE MULTIPLEXING OVER ATM
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
73
Conceptually, the Any-PHY protocol can be divided into two processes: polling
and cell transfer.
Polling in the transmit direction is used by the bus master – typically a traffic
buffering and management device – to determine when a buffered data cell can
be safely sent to a PHY. The S/UNI-IMA-84 provides an independent 3-deep cell
buffer FIFO for each virtual PHY. In total, there are 84 FIFOs. This arrangement
ensures that there is no head-of-line blocking, while providing latitude to the
master for servicing high data rate ports as well as low data rate ports.
The traffic manager need only poll those virtual PHYs for which it has cells
queued. A cell transfer can be initiated after a polled virtual PHY asserts the TPA
output. Each virtual PHY’s cell buffer availability status (i.e., the status that will be
driven onto the TPA output when the virtual PHY is polled) is deasserted when
the first byte of the last cell is written into the buffer. It is re-asserted only when
the FIFO can accept another complete cell.
In Any-PHY mode, polling is performed using the TADR[10:0] bus in conjunction
with the TCSB. Each S/UNI-IMA-84 uses the TADR[6:0] bits to indicate the 84
logical virtual PHYs. The upper bits from the TADR bus, TADR[10:7], are
compared to the configured address to select the device. The remaining address
bits from the traffic manager are decoded externally and are used to drive the
TCSB. The address prepend field in the cell transfer contains the entire 16-bit
address. In 8-bit mode, the prepend address is reduced to 8-bits.
In Any-PHY mode, the cell transfer is initiated after a successful poll. The virtual
PHY address is prepended to the cell, thus performing an inband selection. The
S/UNI-IMA-84 monitors the address prepend on the cell transfer to detect its
cells.
10.1.1.3
Transmit Cell Transfer Format
The Transmit Cell Transfer Format is shown in Figure 5 and Figure 6. Word/byte
0 is required for cell transfers to an Any-PHY slave. The address prepend is the
S/UNI-IMA-84 virtual PHY ID. The virtual PHY ID can be mapped to a TC link or
to an IMA group. Optional prepends are supported, but are ignored by the S/UNI-
IMA-84.
Inclusion of optional words is statically configurable for the interface. The optional
words are always ignored.