UM10503
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© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
548 of 1269
NXP Semiconductors
UM10503
Chapter 23: LPC43xx USB0 Host/Device/OTG controller
consumption rate, then software can reduce the SOF length using the USB0FLADJ
register. The USB bit clock is still running at the normal rate so no bus errors occur. The
host only changes when it introduces the next SOF token - earlier or later on a bit-time
resolution boundary. Adding the SOF token early allows to obtain more data over the
course of the transmission.
The registers to control the frame length are located in the CREG block (see
23.7.8 Hardware assist
The hardware assist provides automated response and sequencing that may not be
possible in software if there are significant interrupt latency response times. The use of
this additional circuitry is optional and can be used to assist the following three state
transitions by setting the appropriate bits in the OTGSC register:
•
Auto reset (set bit HAAR).
•
Data pulse (set bit HADP).
•
B-disconnect to A-connect (set bit HABA).
23.7.8.1 Auto reset
When the HAAR in the OTGSC register is set to one, the host will automatically start a
reset after a connect event. This shortcuts the normal process where software is notified
of the connect event and starts the reset. Software will still receive notification of the
connect event (CCS bit in the PORTSC register) but should not write the reset bit in the
USBCMD register when the HAAR is set. Software will be notified again after the reset is
complete via the enable change bit in the PORTSC register which causes a port change
interrupt.
This assist will ensure the OTG parameter TB_ACON_BSE0_MAX = 1 ms is met (see
OTG specification
for an explanation of the OTG timing requirements).
23.7.8.2 Data pulse
Writing a one to HADP in the OTGSC register will start a data pulse of approximately 7 ms
in duration and then automatically cease the data pulsing. During the data pulse, the DP
bit will be set and then cleared. This automation relieves software from accurately
controlling the data-pulse duration. During the data pulse, the HCD can poll to see that the
HADP and DP bit have returned low to recognize the completion, or the HCD can simply
launch the data pulse and wait to see if a VBUS Valid interrupt occurs when the A-side
supplies bus power.
This assist will ensure data pulsing meets the OTG requirement of > 5 ms and < 10 ms.
23.7.8.3 B-disconnect to A-connect (Transition to the A-peripheral state)
During HNP, the B-disconnect occurs from the OTG A_suspend state, and within 3 ms,
the A-device must enable the pull-up on the DP leg in the A-peripheral state. For the
hardware assist to begin the following conditions must be met:
•
HABA is set.
•
Host controller is in suspend mode.
•
Device is disconnecting.