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UM10503
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© NXP B.V. 2015. All rights reserved.
User manual
Rev. 2.1 — 10 December 2015
747 of 1441
NXP Semiconductors
UM10503
Chapter 26: LPC43xx/LPC43Sxx USB1 Host/Device controller
26.6.10 Transfer buffer Fill Tuning register (TXFILLTUNING)
26.6.10.1 Device controller
This register is not used in device mode.
26.6.10.2 Host controller
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 “backoff”
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). Backoffs can be minimized
with use of the TSCHHEALTH (T
ff
) described below.
Table 545. USB burst size register in device/host mode (BURSTSIZE - address 0x4000 7160) bit description
Bit
Symbol
Description
Reset
value
Access
7:0
RXPBURST
Programmable RX burst length
This register represents the maximum length of a burst in 32-bit words while
moving data from the USB bus to system memory.
0x10
R/W
15:8
TXPBURST
Programmable TX burst length
This register represents the maximum length of a burst in 32-bit words while
moving data from system memory to the USB bus.
0x10
R/W
31:16
-
reserved
-
-