UM10360 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
User manual Rev. 3 — 19 December 2013 297 of 841
NXP Semiconductors
UM10360
Chapter 13: LPC176x/5x USB OTG
The dev_dma_need_clk signal is asserted on any Device controller DMA access to
memory. Once asserted, it remains active for 2 ms (2 frames), to help assure that DMA
throughput is not affected by any latency associated with re-enabling ahb_master_clk.
2 ms after the last DMA access, dev_dma_need_clk is de-asserted to help conserve
power. This signal allows AHB_CLK_EN to be cleared during normal operation.
13.10.1.1 Host clock request signals
The Host controller has two clock request signals, host_need_clk and
host_dma_need_clk. When asserted, these signals turn on the host’s 48 MHz clock and
ahb_master_clk respectively.
The host_need_clk signal is asserted while the Host controller functional state is not
UsbSuspend, or if the functional state is UsbSuspend and resume signaling or a
disconnect is detected on the USB bus. This signal allows HOST_CLK_EN to be cleared
during normal operation when software does not need to access the Host controller
registers – the Host will continue to function normally and automatically shut off its clock
when it goes into the UsbSuspend state.
The host_dma_need_clk signal is asserted on any Host controller DMA access to
memory. Once asserted, it remains active for 2 ms (2 frames), to help assure that DMA
throughput is not affected by any latency associated with re-enabling ahb_master_clk.
2 ms after the last DMA access, host_dma_need_clk is de-asserted to help conserve
power. This signal allows AHB_CLK_EN to be cleared during normal operation.
13.10.2 Power-down mode support
The LPC176x/5x can be configured to wake up from Power-down mode on any USB bus
activity. When the chip is in Power-down mode and the USB interrupt is enabled, the
assertion of USB_NEED_CLK causes the chip to wake up from Power-down mode.
Before Power-down mode can be entered when the USB activity interrupt is enabled,
USB_NEED_CLK must be de-asserted. This is accomplished by clearing all of the
CLK_EN bits in OTGClkCtrl and putting the Host controller into the UsbSuspend
functional state. If it is necessary to wait for either of the dma_need_clk signals or the
dev_need_clk to be de-asserted, the status of USB_NEED_CLK can be polled in the
USBIntSt register to determine when they have all been de-asserted.
13.11 USB OTG controller initialization
The LPC176x/5x OTG device controller initialization includes the following steps:
1. Enable the device controller by setting the PCUSB bit of PCONP.
2. Configure and enable the USB PLL (PLL1) or Main PLL (PLL0) to provide 48 MHz for
usbclk and the desired frequency for cclk. For the procedure for determining the PLL
setting and configuration, see Section 4.5.11 “
Procedure for determining PLL0
settings” or Section 4.6.9 “Procedure for determining PLL1 settings”.
3. Enable the desired controller clocks by setting their respective CLK_EN bits in the
USBClkCtrl register. Poll the corresponding CLK_ON bits in the USBClkSt register
until they are set.
4. Enable the desired USB pin functions by writing to the corresponding PINSEL
registers.
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