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UM10503
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© NXP B.V. 2015. All rights reserved.
User manual
Rev. 2.1 — 10 December 2015
748 of 1441
NXP Semiconductors
UM10503
Chapter 26: LPC43xx/LPC43Sxx USB1 Host/Device controller
26.6.11 USB ULPI viewport register (ULPIVIEWPORT)
The register provides indirect access to the ULPI PHY register set. Although the core
performs access to the ULPI PHY register set, there may be extraordinary circumstances
where software may need direct access.
Remark:
Writes to the ULPI through the viewport can substantially harm standard USB
operations. Currently no usage model has been defined where software should need to
execute writes directly to the ULPI – see exception regarding optional features below.
Remark:
Executing read operations though the ULPI viewport should have no harmful
side effects to standard USB operations.
There are two operations that can be performed with the ULPI Viewport, wake-up and
read /write operations. The wakeup operation is used to put the ULPI interface into normal
operation mode and reenable the clock if necessary. A wakeup operation is required
before accessing the registers when the ULPI interface is operating in low power mode,
serial mode, or carkit mode. The ULPI state can be determined by reading the sync. state
bit (ULPISS). If this bit is a one, then ULPI interface is running in normal operation mode
and can accept read/write operations. If the ULPISS indicates a 0 then read/write
Table 546. USB Transfer buffer Fill Tuning register in host mode (TXFILLTUNING - address 0x4000 7164) bit
description
Bit
Symbol
Description
Reset
value
Access
7:0
TXSCHOH
FIFO burst threshold
This register controls the number of data bursts that are posted to the TX
latency FIFO in host mode before the packet begins on to the bus. The
minimum value is 2 and this value should be a low as possible to maximize
USB performance. A higher value can be used in systems with unpredictable
latency and/or insufficient bandwidth where the FIFO may underrun because
the data transferred from the latency FIFO to USB occurs before it can be
replenished from system memory. This value is ignored if the Stream Disable
bit in USBMODE register is set.
0x2
R/W
12:8
TXSCHEATLTH
Scheduler health counter
This register increments when the host controller fails to fill the TX latency
FIFO to the level programmed by TXFIFOTHRES before running out of time
to send the packet before the next Start-Of-Frame .
This health counter measures the number of times this occurs to provide
feedback to selecting a proper TXSCHOH. Writing to this register will clear the
counter. The maximum value is 31.
0x0
R/W
15:13
-
Reserved
-
-
21:16
TXFIFOTHRES
Scheduler overhead
This register adds an additional fixed offset to the schedule time estimator
described above as T
ff
. As an approximation, the value chosen for this register
should limit the number of back-off events captured in the TXSCHHEALTH to
less than 10 per second in a highly utilized bus. Choosing a value that is too
high for this register is not desired as it can needlessly reduce USB utilization.
The time unit represented in this register is 1.267
s when a device is
connected in High-Speed Mode.
The time unit represented in this register is 6.333
s when a device is
connected in Low/Full Speed Mode.
0x0
R/W
31:22
-
Reserved