Figure 367. Bulk Out Transaction - ST STM32F207 Series Reference Manual

USB on-the-go full-speed (OTG_FS)
Figure 367
and describes the events involved in the process.
Host
After a SetConfiguration/SetInterface command, the application initializes all OUT endpoints
by setting CNAK = 1 and EPENA = 1 (in OTG_FS_DOEPCTLx), and setting a suitable
XFRSIZ and PKTCNT in the OTG_FS_DOEPTSIZx register.
1. host attempts to send data (OUT token) to an endpoint.
2. When the core receives the OUT token on the USB, it stores the packet in the RxFIFO
because space is available there.
3. After writing the complete packet in the RxFIFO, the core then asserts the RXFLVL
interrupt (in OTG_FS_GINTSTS).
4. On receiving the PKTCNT number of USB packets, the core internally sets the NAK bit
for this endpoint to prevent it from receiving any more packets.
5. The application processes the interrupt and reads the data from the RxFIFO.
6. When the application has read all the data (equivalent to XFRSIZ), the core generates
an XFRC interrupt (in OTG_FS_DOEPINTx).
7. The application processes the interrupt and uses the setting of the XFRC interrupt bit
(in OTG_FS_DOEPINTx) to determine that the intended transfer is complete.
IN data transfers
•
Packet write
This section describes how the application writes data packets to the endpoint FIFO when
dedicated transmit FIFOs are enabled.
1. The application can either choose the polling or the interrupt mode.
1082/1381
depicts the reception of a single Bulk OUT Data packet from the USB to the AHB

Figure 367. Bulk OUT transaction

USB Device
2
3
64 bytes
xact _1
5
7
RM0033 Rev 9
Application
init_ out_ ep
1
wr_reg (DOEPTSIZx)
wr_reg(D OEPCTLx)
4
6
RXFLVL intr i
idle until intr
rcv_out _pkt()
idle until intr
8
RM0033
XFRSIZ = 64 bytes
PKTCNT = 1
EPENA = 1
CNAK = 1
On new xfer
or RxFIFO
not empty
ai15679b