RM0090 Rev 18 1255/1749
RM0090 USB on-the-go full-speed (OTG_FS)
1380
responsible for the management of the periodic and nonperiodic request queues.The
periodic transmit FIFO and queue status register (HPTXSTS) and nonperiodic transmit
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
SB 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_FS_HNPTXSTS register or NPTQXSAV bits in the
OTG_FS_HNPTXSTS register.
34.7 SOF trigger
Figure 390. SOF connectivity
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.
34.7.1 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
STM32 MCU
VBUS
D
+
V
SS
PA8
PA1 2
PA1 1
USB mic ro-AB connector
D
-
IDTIM2
ITR1 SOF
pulse
SOFgen
PA9
PA1 0
SOF pulse output, to
external audio control
MS19907V3
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