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9−5
Table 9−3. Link Enhancement Register Description (Continued)
BIT FIELD NAME TYPE DESCRIPTION
9 RSVD R Reserved. Bit 9 returns 0 when read.
8 ‡ enab_dv_ts RW
Enable DV CIP timestamp enhancement. When bit 8 is set to 1, the enhancement is enabled for DV
CIP transmit streams (FMT = 00h). The default value for this bit is 0.
7 ‡ enab_unfair RW
Enable asynchronous priority requests. OHCI-Lynx compatible. Setting bit 7 to 1 enables the link to
respond to requests with priority arbitration. It is recommended that this bit be set to 1. The default value
for this bit is 0.
6 RSVD R
This bit is not assigned in the PCI7x21/PCI7x11 follow-on products, because this bit location loaded
by the serial EEPROM from the enhancements field corresponds to bit 23 (programPhyEnable) in the
host controller control register at OHCI offset 50h/54h (see Section 8.16).
5−3 RSVD R Reserved. Bits 5−3 return 0s when read.
2 ‡ RSVD R Reserved. Bit 2 returns 0 when read.
1 ‡ enab_accel RW
Enable acceleration enhancements. OHCI-Lynx compatible. When bit 1 is set to 1, the PHY layer
is notified that the link supports the IEEE Std 1394a-2000 acceleration enhancements, that is,
ack-accelerated, fly-by concatenation, etc. It is recommended that this bit be set to 1. The default value
for this bit is 0.
0 RSVD R Reserved. Bit 0 returns 0 when read.
‡
This bit is cleared only by the assertion of GRST
.
9.5 Timestamp Offset Register
The value of this register is added as an offset to the cycle timer value when using the MPEG, DV, and CIP
enhancements. A timestamp offset register is implemented per isochronous transmit context. The n value following
the offset indicates the context number (n = 0, 1, 2, 3, …, 7). These registers are programmed by software as
appropriate. See Table 9−4 for a complete description of the register contents.
Bit 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
Name Timestamp offset
Type RW R R R R R R RW RW RW RW RW RW RW RW RW
Default 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Name Timestamp offset
Type RW RW RW RW RW RW RW RW RW RW RW RW RW RW RW RW
Default 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Register: Timestamp offset
Offset: A90h + (4*n)
Type: Read/Write, Read-only
Default: 0000 0000h
Table 9−4. Timestamp Offset Register Description
BIT FIELD NAME TYPE DESCRIPTION
31 DisableInitialOffset RW Bit 31 disables the use of the initial timestamp offset when the MPEG2 enhancements are enabled.
A value of 0 indicates the use of the initial offset, a value of 1 indicates that the initial offset must not
be applied to the calculated timestamp. This bit has no meaning for the DV timestamp
enhancements. The default value for this bit is 0.
30−25 RSVD R Reserved. Bits 30−25 return 0s when read.
24−12 CycleCount RW This field adds an offset to the cycle count field in the timestamp when the DV or MPEG2
enhancements are enabled. The cycle count field is incremented modulo 8000; therefore, values in
this field must be limited between 0 and 7999. The default value for this field is all 0s.
11−0 CycleOffset RW This field adds an offset to the cycle offset field in the timestamp when the DV or MPEG2
enhancements are enabled. The cycle offset field is incremented modulo 3072; therefore, values in
this field must be limited between 0 and 3071. The default value for this field is all 0s.