TSB41AB1PAP Datasheet, PDF (47/69 Pages) Texas Instruments – IEEE 1394a-2000 ONE-PORT CABLE

TSB41AB1
IEEE 1394aĆ2000 ONEĆPORT CABLE
TRANSCEIVER/ARBITER
SLLS423I − JUNE 2000 − REVISED MARCH 2005
PRINCIPLES OF OPERATION
LLC service request (continued)
The LLC may make only one bus request at a time. Once the LLC issues any request for bus access (ImmReq,
IsoReq, FairReq, or PriReq), it cannot issue another bus request until the PHY indicates that the bus request
was lost (bus arbitration lost and another packet received), or won (bus arbitration won and the LLC granted
control). The PHY ignores new bus requests while a previous bus request is pending. All bus requests are
cleared upon a bus reset.
For write register requests, the PHY loads the specified data into the addressed register as soon as the request
transfer is complete. For read register requests, the PHY returns the contents of the addressed register to the
LLC at the next opportunity through a status transfer. If a received packet interrupts the status transfer, then the
PHY continues to attempt the transfer of the requested register until it is successful. A write or read register
request may be made at any time, including while a bus request is pending. Once a read register request is
made, the PHY ignores further read register requests until the register contents are successfully transferred to
the LLC. A bus reset does not clear a pending read register request.
The TSB41AB1 includes several arbitration acceleration enhancements, which allow the PHY to improve bus
performance and throughput by reducing the number and length of interpacket gaps. These enhancements
include autonomous (fly-by) isochronous packet concatenation, autonomous fair and priority packet
concatenation onto acknowledge packets, and accelerated fair and priority request arbitration following
acknowledge packets. The enhancements are enabled when the EAA bit in PHY register 5 is set.
The arbitration acceleration enhancements may interfere with the ability of the cycle master node to transmit
the cycle start message under certain circumstances. The acceleration control request is therefore provided
to allow the LLC to temporarily enable or disable the arbitration acceleration enhancements of the TSB41AB1
during the asynchronous period. The LLC typically disables the enhancements when its internal cycle counter
rolls over indicating that a cycle start message is imminent, and then reenables the enhancements when it
receives a cycle start message. The acceleration control request may be made at any time, however, and is
immediately serviced by the PHY. Additionally, a bus reset or isochronous bus request causes the
enhancements to be reenabled, if the EAA bit is set.
status transfer
A status transfer is initiated by the PHY when there is status information to be transferred to the LLC. The PHY
waits until the interface is idle before starting the transfer. The transfer is initiated by the PHY asserting status
(01b) on the CTL terminals, along with the first two bits of status information on the D0 and D1 terminals. The
PHY maintains CTL = status for the duration of the status transfer. The PHY may prematurely end a status
transfer by asserting something other than status on the CTL terminals. This occurs if a packet is received before
the status transfer completes. The PHY continues to attempt to complete the transfer until all status information
has been successfully transmitted. There is at least one idle cycle between consecutive status transfers.
The PHY normally sends just the first four bits of status to the LLC. These bits are status flags that are needed
by the LLC state machines. The PHY sends an entire 16-bit status packet to the LLC after a read register
request, or when the PHY has pertinent information to send to the LLC or transaction layers. The only defined
condition where the PHY automatically sends a register to the LLC is after self-ID, where the PHY sends the
physical-ID register that contains the new node address. All status transfers are either 4 or 16 bits unless
interrupted by a received packet. The status flags are considered to have been successfully transmitted to the
LLC immediately upon being sent, even if a received packet subsequently interrupts the status transfer. Register
contents are considered to have been successfully transmitted only when all 8 bits of the register have been
sent. A status transfer is retried after being interrupted only if any status flags remain to be sent, or if a register
transfer has not yet completed.
The definitions of the bits in the status transfer are shown in Table 19, and the timing is shown in Figure 22.
• POST OFFICE BOX 655303 DALLAS, TEXAS 75265
• POST OFFICE BOX 1443 HOUSTON, TEXAS 77251−1443
47