ST STM32F207 Series Reference Manual page 1006

USB on-the-go full-speed (OTG_FS)
Bit 31 Reserved, must be kept at reset value.
Bits 30:24 NPTXQTOP: Top of the non-periodic transmit request queue
Bits 23:16 NPTQXSAV: Non-periodic transmit request queue space available
Bits 15:0 NPTXFSAV: Non-periodic TxFIFO space available
OTG_FS general core configuration register (OTG_FS_GCCFG)
Address offset: 0x038
Reset value: 0x0000 XXXX
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
Reserved
1006/1381
Entry in the non-periodic Tx request queue that is currently being processed by the MAC.
Bits 30:27: Channel/endpoint number
Bits 26:25:
– 00: IN/OUT token
– 01: Zero-length transmit packet (device IN/host OUT)
– 11: Channel halt command
Bit 24: Terminate (last entry for selected channel/endpoint)
Indicates the amount of free space available in the non-periodic transmit request queue.
This queue holds both IN and OUT requests in host mode. Device mode has only IN
requests.
00: Non-periodic transmit request queue is full
01: 1 location available
10: 2 locations available
bxn: n locations available (0 ≤ n ≤ 8)
Others: Reserved
Indicates the amount of free space available in the non-periodic TxFIFO.
Values are in terms of 32-bit words.
00: Non-periodic TxFIFO is full
01: 1 word available
10: 2 words available
0xn: n words available (where 0 ≤ n ≤ 256)
Others: Reserved
rw rw rw rw rw
RM0033 Rev 9
9 8 7 6 5 4 3
Reserved
RM0033
2 1 0