RM0090: Reference manual - STMicroelectronics

RM0090 USB on-the-go high-speed (OTG_HS)
FIFO and queue status register (HNPTXSTS) are read-only registers which can be used by
the application to read the status of each request queue. They contain:
● The number of free entries currently available in the periodic (nonperiodic) request
queue (8 max)
● Free space currently available in the periodic (nonperiodic) Tx-FIFO (out-transactions)
● IN/OUT token, host channel number and other status information.
As request queues can hold a maximum of 8 entries each, the application can push to
schedule host transactions in advance with respect to the moment they physically reach the
USB for a maximum of 8 pending periodic transactions plus 8 pending nonperiodic
transactions.
To post a transaction request to the host scheduler (queue) the application must check that
there is at least 1 entry available in the periodic (nonperiodic) request queue by reading the
PTXQSAV bits in the OTG_HS_HNPTXSTS register or NPTQXSAV bits in the
OTG_HS_HNPTXSTS register.
31.7 SOF trigger
The OTG FS core allows to monitor, track and configure SOF framing in the host and
peripheral. It also features an SOF pulse output connectivity.
These capabilities are particularly useful to implement adaptive audio clock generation
techniques, where the audio peripheral needs to synchronize to the isochronous stream
provided by the PC, or the host needs trimming its framing rate according to the
requirements of the audio peripheral.
31.7.1 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 (OTG_HS_HFIR), thus providing application control over the SOF framing period.
An interrupt is generated at any start of frame (SOF bit in OTG_HS_GINTSTS). The current
frame number and the time remaining until the next SOF are tracked in the host frame
number register (OTG_HS_HFNUM).
An SOF pulse signal is generated at any SOF starting token and with a width of 12 system
clock cycles. It 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
through ITR1_RMP bits of TIM2_OR register.
Doc ID 018909 Rev 3 1168/1416