Data Sheet, Rev. 1
February 2001
FW322
1394A PCI PHY/Link Open Host Controller Interface
FW322 Functional Description (continued)
sends the asynchronous interrupt status to the OHCI
interrupt handler block.
Asynchronous Transmit (ASYNC_TX)
The ASYNC_TX block of the FW322 manages the
asynchronous transmission of either request or
response packets. The mechanism for asynchronous
transmission of requests and responses are similar.
The only difference is the system memory location of
the buffer descriptor list when processing the two con-
texts. Therefore, the discussion below, which is for
asynchronous transmit requests, parallels that of the
asynchronous transmit response. The FW322 asyn-
chronous transmission of packets involves the following
steps:
1. Fetch complete buffer descriptor block from host
memory.
2. Get data from system memory and store into
async FIFO.
3. Request transfer of data from FIFO to link device.
4. Handle retries, if any.
5. Handle errors in steps 1 to 4.
6. End the transfer if there are no errors.
Asynchronous Receive (ASYNC_RX)
The ASYNC_RX block of the FW322 manages the
processing of received packets. Data packets are
parsed and stored in a dedicated asynchronous receive
FIFO. Command descriptors are read through the PCI
interface to determine the disposition of the data
arriving through the 1394 link.
The header of the received packet is processed to
determine, among other things, the following:
1. The type of packet received.
2. The source and destinations.
3. The data and size, if any.
4. The operation required, if any. For example, compare
and swap operation.
The ASYNC block also handles DMA transfers of self-
ID packets during the 1394 bus initialization phase and
block transactions associated with physical request.
Link Core
It is the responsibility of the link to ascertain if a
received packet is to be forwarded to the OHCI for
processing. If so, the packet is directed to a proper
inbound FIFO for either the isochronous block or the
asynchronous block to process. The link is also
responsible for CRC generation on outgoing packets
and CRC checking on receiving packets.
To become aware of data to be sent outbound on
1394 bus, the link must monitor the OHCI FIFOs look-
ing for packets in need of transmission. Based on data
received from the OHCI block, the link will form packet
headers for the 1394 bus. The link will alert the PHY
core as to the availability of the outbound data. It is the
link’s function to generate CRC for the outbound data.
The link also provides PHY core register access for the
OHCI.
PHY Core
The PHY core provides the analog physical layer func-
tions needed to implement a two-port node in a cable-
based IEEE 1394-1995 and IEEE 1394a-2000 network.
Each cable port incorporates two differential line trans-
ceivers. The transceivers include circuitry to monitor the
line conditions as needed for determining connection
status, for initialization and arbitration, and for packet
reception and transmission. The PHY core interfaces
with the link core.
The PHY core requires either an external 24.576 MHz
crystal or crystal oscillator. The internal oscillator drives
an internal phase-locked loop (PLL), which generates
the required 400 MHz reference signal. The 400 MHz
reference signal is internally divided to provide the
49.152 MHz, 98.304 MHz, and 196.608 MHz clock sig-
nals that control transmission of the outbound encoded
strobe and data information. The 49.152 MHz clock sig-
nal is also supplied to the associated LLC for
synchronization of the two chips and is used for resyn-
chronization of the received data.
The PHY/link interface is a direct connection and does
not provide isolation.
Data bits to be transmitted through the cable ports are
received from the LLC on two, four, or eight data lines
(D[0:7]), and are latched internally in the PHY in syn-
chronization with the 49.152 MHz system clock. These
bits are combined serially, encoded, and transmitted at
98.304 Mbits/s, 196.608 Mbits/s, or 393.216 Mbits/s as
the outbound data-strobe information stream. During
transmission, the encoded data information is transmit-
ted differentially on the TPA and TPB cable pair(s).
During packet reception, the TPA and TPB transmitters
of the receiving cable port are disabled, and the receiv-
ers for that port are enabled. The encoded data
information is received on the TPA and TPB cable pair.
The received data-strobe information is decoded to
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