Sof Trigger; Host Sofs; Peripheral Sofs; Figure 306. Sof Connectivity - ST STM32F101 series Reference Manual

RM0008
PTXQSAV bits in the OTG_FS_HNPTXSTS register or NPTQXSAV bits in the
OTG_FS_HNPTXSTS register.
28.7

SOF trigger

The OTG FS core provides means to monitor, track and configure SOF framing in the host
and peripheral, as well as an SOF pulse output connectivity feature.
Such utilities are especially useful for adaptive audio clock generation techniques, where
the audio peripheral needs to synchronize to the isochronous stream provided by the PC, or
the host needs to trim its framing rate according to the requirements of the audio peripheral.
28.7.1

Host SOFs

In host mode the number of PHY clocks occurring between the generation of two
consecutive SOF (FS) or Keep-alive (LS) tokens is programmable in the host frame interval
register (HFIR), thus providing application control over the SOF framing period. An interrupt
is generated at any start of frame (SOF bit in OTH_FS_GINTSTS). The current frame
number and the time remaining until the next SOF are tracked in the host frame number
register (HFNUM).
An SOF pulse signal, generated at any SOF starting token and with a width of 12 system
clock cycles, can be made available externally on the SOF pin using the SOFOUTEN bit in
the global control and configuration register. The SOF pulse is also internally connected to
the input trigger of timer 2 (TIM2), so that the input capture feature, the output compare
feature and the timer can be triggered by the SOF pulse. The TIM2 connection is enabled by
register.
28.7.2

Peripheral SOFs

In device mode, the start of frame interrupt is generated each time an SOF token is received
on the USB (SOF bit in OTH_FS_GINTSTS). The corresponding frame number can be read
from the device status register (FNSOF bit in OTG_FS_DSTS). An SOF pulse signal with a
width of 12 system clock cycles is also generated and can be made available externally on
the SOF pin by using the SOF output enable bit in the global control and configuration

Figure 306. SOF connectivity

STM32F105xx
STM32F107xx
ITR1 SOF
pulse
SOFgen
TIM2
DocID13902 Rev 15
USB on-the-go full-speed (OTG_FS)
SOF pulse output, to
PA8
external audio control
PA9
PA11
PA12
PA10
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