ST STM32F405 Reference Manual page 1428

USB on-the-go high-speed (OTG_HS)
Bit 31 Reserved, must be kept at reset value.
Bits 30:24 NPTXQTOP: Top of the nonperiodic transmit request queue
Bits 23:16 NPTQXSAV: Nonperiodic transmit request queue space available
Bits 15:0 NPTXFSAV: Nonperiodic TxFIFO space available
OTG_HS general core configuration register (OTG_HS_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
1428/1749
Entry in the nonperiodic 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)
– 10: PING/CSPLIT token
– 11: Channel halt command
Bit [24]: Terminate (last entry for selected channel/endpoint)
Indicates the amount of free space available in the nonperiodic transmit request queue.
This queue holds both IN and OUT requests in host mode. Peripheral mode has only IN
requests.
00: Nonperiodic transmit request queue is full
01: dx1 location available
10: dx2 locations available
bxn: dxn locations available (0 ≤ n ≤ dx8)
Others: Reserved
Indicates the amount of free space available in the nonperiodic TxFIFO.
Values are in terms of 32-bit words.
00: Nonperiodic TxFIFO is full
01: dx1 word available
10: dx2 words available
0xn: dxn words available (where 0 ≤ n ≤ dx1024)
Others: Reserved
rw rw rw rw rw rw
RM0090 Rev 18
9 8 7 6 5 4 3
Reserved
RM0090
2 1 0