Dynamic Update Of The Otg_Hfir Register; Usb Data Fifos; Figure 400. Updating Otg_Hfir Dynamically (Rldctrl = 0) - ST STM32F423 Reference Manual

RM0430
the USB clock switching activity is cut even if the system clock is kept running by the
application for other purposes.
•
USB system stop
When the OTG_FS is in the USB suspended state, the application may decide to
drastically reduce the overall power consumption by a complete shut down of all the
clock sources in the system. USB System Stop is activated by first setting the Stop
PHY clock bit and then configuring the system deep sleep mode in the power control
system module (PWR).
The OTG_FS core automatically reactivates both system and USB clocks by
asynchronous detection of remote wakeup (as an host) or resume (as a device)
signaling on the USB.
To save dynamic power, the USB data FIFO is clocked only when accessed by the OTG_FS
core.
33.10

Dynamic update of the OTG_HFIR register

The USB core embeds a dynamic trimming capability of SOF framing period in host mode
allowing to synchronize an external device with the SOF frames.
When the OTG_HFIR register is changed within a current SOF frame, the SOF period
correction is applied in the next frame as described in
For a dynamic update, it is required to set RLDCTRL=0.
33.11

USB data FIFOs

The USB system features 1.25 Kbytes of dedicated RAM with a sophisticated FIFO control
mechanism. The packet FIFO controller module in the OTG_FS core organizes RAM space
into Tx FIFOs into which the application pushes the data to be temporarily stored before the
USB transmission, and into a single Rx FIFO where the data received from the USB are
temporarily stored before retrieval (popped) by the application. The number of instructed
FIFOs and how these are organized inside the RAM depends on the device's role. In
peripheral mode an additional Tx FIFO is instructed for each active IN endpoint. Any FIFO
size is software configured to better meet the application requirements.

Figure 400. Updating OTG_HFIR dynamically (RLDCTRL = 0)

RM0430 Rev 8
USB on-the-go full-speed (OTG_FS)
Figure 400.
1149/1324
1283