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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
August 2006
Developer’s Manual
Order Number: 306262--, Revision: 004US
381
USB 2.0 Host Controller—Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
9.12.9
TXFILLTUNING
Address:
Base + 164h
Default Value: 0x00020000
Attribute:
Read/Write (Writes must be DWord Writes)
Size:
32 bits
The fields in this register control performance tuning associated with how the host
controller posts data to the TX latency FIFO before moving the data onto the USB bus.
The specific areas of performance include the how much data to post into the FIFO and
an estimate for how long that operation should take in the target system.
Definitions:
• T
0
= Standard packet overhead
• T
1
= Time to send data payload
• T
ff
= Time to fetch packet into TX FIFO up to specified level.
• T
s
= Total Packet Flight Time (send-only) packet
• T
s
= T
0
+ T
1
• T
p
= Total Packet Time (fetch and send) packet
• T
p
= T
ff
+ T
0
+ T
1
Upon discovery of a transmit (OUT/SETUP) packet in the data structures, host
controller checks to ensure T
p
remains before the end of the [micro]frame. If so it
proceeds to pre-fill the TX FIFO. If at anytime during the pre-fill operation the time
remaining the [micro]frame is < T
s
then the packet attempt ceases and the packet is
tried at a later time. Although this is not an error condition and the host controller will
eventually recover, a mark will be made the scheduler health counter to note the
occurrence of a “back-off” event. When a back-off event is detected, the partial packet
fetched may need to be discarded from the latency buffer to make room for periodic
traffic that will begin after the next SOF. Too many back-off events can waste
bandwidth and power on the system bus and thus should be minimized (not necessarily
eliminated). Back-offs can be minimized with use of the TSCHHEALTH (T
ff
) described
below.
9.12.10
CONFIGFLAG
Address:
Base + 180h
Table 140.
BURSTSIZE - Host Controller Embedded TT Async. Buffer Status
Field
Description
(Reserved)
These bits are reserved and their value has no effect on operation.
TXPBURST
Programmable TX Burst Length. (Read/Write) Default is the constant
VUSB_HS_TX_BURST. This register represents the maximum length of a the burst in 32-
bit words while moving data from system memory to the USB bus.
RXPBURST
Programmable RX Burst Length. (Read/Write) Default is the constant
VUSB_HS_RX_BURST. This register represents the maximum length of a the burst in 32-bit
words while moving data from the USB bus to system memory.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
8
7
6
5
4
3
2
1
0
(Reserved)
TXFIFOTHRES
(Rsvd)
TXSCHEALTH
TXSCHOH