ST STM32L4x6 Reference Manual page 1553

RM0351
Bits 31:17 Reserved, must be kept at reset value.
Bit 16 RLDCTRL: Reload control
This bit allows dynamic reloading of the HFIR register during run time.
0: The HFIR cannot be reloaded dynamically
1: The HFIR can be dynamically reloaded during runtime.
This bit needs to be programmed during initial configuration and its value must not be
changed during runtime.
Bits 15:0 FRIVL: Frame interval for USB OTG FS
The value that the application programs to this field, specifies the interval between two
consecutive SOFs (FS) or Keep-Alive tokens (LS). This field contains the number of PHY
clocks that constitute the required frame interval. The application can write a value to this
register only after the Port enable bit of the host port control and status register (PENA bit in
OTG_HPRT) has been set. If no value is programmed, the core calculates the value based
on the PHY clock specified in the FS/LS PHY Clock Select field of the host configuration
register (FSLSPCS in OTG_HCFG). Do not change the value of this field after the initial
configuration, unless the RLDCTRL bit is set. In such case, the FRIVL is reloaded with each
SOF event.
43.15.22 OTG Host frame number/frame time remaining register
(OTG_HFNUM)
Address offset: 0x408
Reset value: 0x0000 3FFF
This register indicates the current frame number. It also indicates the time remaining (in
terms of the number of PHY clocks) in the current frame.
31 30 29
r r r
15 14 13
r r r
Bits 31:16 FTREM: Frame time remaining
Bits 15:0 FRNUM: Frame number
28 27 26 25
r r r r
12 11 10 9
r r r r
Indicates the amount of time remaining in the current frame, in terms of PHY clocks. This
field decrements on each PHY clock. When it reaches zero, this field is reloaded with the
value in the Frame interval register and a new SOF is transmitted on the USB.
This field increments when a new SOF is transmitted on the USB, and is cleared to 0 when
it reaches 0x3FFF.
24 23 22
FTREM
r r r
8 7 6
FRNUM
r r r
DocID024597 Rev 3
USB on-the-go full-speed (OTG_FS)
21 20 19 18
r r r
5 4 3
r r r
17 16
r r r
2 1 0
r r r
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