82C881 Datasheet, PDF (45/46 Pages) List of Unclassifed Manufacturers – FireLink 1394 OHCI Link Controller

10.2.1.2.5 Isochronous Transmit Packet Format
HEADER
DATA
FireLink 1394 OHCI
82C881
10.2.1.2.6 Other Transmit Packet Format
• Transmit packet start delimiter format
Field Name
delimiter
Reserved
C_loadCycCount
C_loadCycSecs
C_CycMatchEnable
Reserved
Width
1
Bit Position
0
7
7:1
13
20:8
3
23:21
1
24
7
31:25
Description
0 – start delimiter
1 – end delimiter
Currently not used
Cycle count field of the Isochronous cycle timer
register (refer to OHCI specification 1.0 chapter
5,section 5-12)
Lower 3 bits of the Cycle seconds field of the
Isochronous cycle timer register (refer to OHCI
specification 1.0 chapter 5,section 5-12)
CycleMatchEnable bit of the IT context control
register
Currently not used
Header and data are as specified in 1394 OHCI specification 1.0
A tag bit is also specified along with each quadlet of the packet. The tag bit distinguishes between a data and delimiter.
[tag=0 (data), tag=1 (delimiter)]
Special consideration should be taken for Tx FIFOs -
As far as Tx FIFO is concerned, except for IT FIFO, no other FIFO writes Start / End Delimiter (Quadlets corr. to Tag bit = 1'b1
) into the DPRAM.
IT FIFO only writes Start Delimiter in the FIFO.
Also except for IT FIFO, in all other Tx FIFOs, at one time only one packet is written into. And the write packet count is reset
after seeing the ack for that packet.
Also, while transmitting non-IT packets, although end Delimiter is not written in the FIFO, it is sensed by the FIFO Controller
logic to increment the packet count. But this cannot be done in debug mode. Hence while writing in debug mode, intended to
be read in normal mode, then the packet size should be greater than the read watermark of the non-IT Tx FIFOs, so that
linkArbRequest get triggered after coming back to normal mode.
When arbitrary data quadlets are written into non-IT Tx FIFOs in debug mode, and then read back also in debug mode, then
also write packet count may mismatch with respect to read packet count. Hence *ArbReq flag can be triggered when returned
to normal mode, even if only 1 quadlet data is written later in the corresponding FIFO. To avoid this, an ack has to be sent for
the packet, even if it is not sent out.
912-2000-031
Revision: 1.0
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