UM10562 Datasheet, PDF (421/942 Pages) NXP Semiconductors – LPC408x/407x User manual

NXP Semiconductors
UM10562
Chapter 14: LPC408x/407x USB OTG controller
14.10.1 Device clock request signals
The Device controller has two clock request signals, dev_need_clk and
dev_dma_need_clk. When asserted, these signals turn on the device’s 48 MHz clock and
ahb_master_clk respectively.
The dev_need_clk signal is asserted while the device is not in the suspend state, or if the
device is in the suspend state and activity is detected on the USB bus. The dev_need_clk
signal is de-asserted if a disconnect is detected (CON bit is cleared in the SIE Get Device
Status register – Section 12.10.6). This signal allows DEV_CLK_EN to be cleared during
normal operation when software does not need to access the Device controller registers –
the Device will continue to function normally and automatically shut off its clock when it is
suspended or disconnected.
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.
14.10.1.1 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.
14.10.2 Power-down mode support
The CPU 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.
UM10562
User manual
All information provided in this document is subject to legal disclaimers.
Rev. 1 — 13 September 2012
© NXP B.V. 2012. All rights reserved.
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