1394 OHCI—PCI Configuration Space
125
March 5 2007 June 2011
SCPS154C
Table 718. Miscellaneous Configuration Register (Continued)
BIT
FIELD NAME
TYPE
DESCRIPTION
1
DISABLE_PCIGATE
RW
Disable PCLK test feature. This bit controls locking or unlocking the PCI clock to the 1394a
OHCI core PCI bus clock input. This is a test feature only and must be cleared to 0b (all
applications).
0 = Hardware decides auto-gating of the PCI clock (default)
1 = Disables auto-gating of the PCI clock
0
KEEP_PCLK
RW
Keep PCI clock running. This bit controls the PCI clock operation during the CLKRUN protocol.
Since the CLKRUN protocol is not supported in the XIO2200A, this bit has no effect. The default
value for this bit is 0b.
These bits are reset by a PCI Express reset (PERST), a GRST, or the internally-generated power-on reset.
7.23 Link Enhancement Control Register
The link enhancement control register implements TI proprietary bits that are initialized by software or by a
serial EEPROM, if present. After these bits are set to 1b, their functionality is enabled only if bit 22
(aPhyEnhanceEnable) in the host controller control register at OHCI offset 50h/54h (see Section
8.16, Host
Controller Control Register) is set to 1. See
Table 719 for a complete description of the register contents.
PCI register offset:
F4h
Register type:
Read/Write, Read-only
Default value:
0000 1000h
BIT NUMBER
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
RESET STATE
0
BIT NUMBER
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
RESET STATE
0
1
0
Table 719. Link Enhancement Control Register Description
BIT
FIELD NAME
TYPE
DESCRIPTION
3116
RSVD
R
Reserved. Bits 3116 return 0000h when read.
15
dis_at_pipeline
RW
Disable AT pipelining. When bit 15 is set to 1b, out-of-order AT pipelining is disabled. The default value
for this bit is 0b.
14
RSVD
RW
Reserved. Bit 14 defaults to 0b and must remain 0b for normal operation of the OHCI core.
1312
atx_thresh
RW
This field sets the initial AT threshold value, which is used until the AT FIFO is underrun. When the OHCI
controller retries the packet, it uses a 2K-byte threshold, resulting in a store-and-forward operation.
00 = Threshold ~ 2K bytes resulting in a store-and-forward operation
01 = Threshold ~ 1.7K bytes (default)
10 = Threshold ~ 1K bytes
11 = Threshold ~ 512 bytes
These bits fine-tune the asynchronous transmit threshold. For most applications the 1.7K-byte
threshold is optimal. Changing this value may increase or decrease the 1394 latency depending on the
average PCI bus latency.
Setting the AT threshold to 1.7K, 1K, or 512 bytes results in data being transmitted at these thresholds
or when an entire packet has been checked into the FIFO. If the packet to be transmitted is larger than
the AT threshold, then the remaining data must be received before the AT FIFO is emptied; otherwise,
an underrun condition occurs, resulting in a packet error at the receiving node. As a result, the link then
commences store-and-forward operation. Wait until it has the complete packet in the FIFO before
retransmitting it on the second attempt to ensure delivery.
An AT threshold of 2K results in store-and-forward operation, which means that asynchronous data will
not be transmitted until an end-of-packet token is received. Restated, setting the AT threshold to 2K
results in only complete packets being transmitted.
Note that the OHCI controller will always use store-and-forward when the asynchronous transmit
retries register at OHCI offset 08h (see Section
8.3, Asynchronous Transmit Retries Register) is
cleared.
These bits are reset by a PCI Express reset (PERST), a GRST, or the internally-generated power-on reset.
Not Recommended for New Designs