Figure 404. Transmit Fifo Write Task - ST STM32F423 Reference Manual

RM0430
Operational model
The application must initialize a channel before communicating to the connected device.
This section explains the sequence of operation to be performed for different types of USB
transactions.
•
Writing the transmit FIFO
The OTG_FS host automatically writes an entry (OUT request) to the periodic/non-
periodic request queue, along with the last 32-bit word write of a packet. The
application must ensure that at least one free space is available in the periodic/non-
periodic request queue before starting to write to the transmit FIFO. The application
must always write to the transmit FIFO in 32-bit words. If the packet size is non-32-bit
word aligned, the application must use padding. The OTG_FS host determines the
actual packet size based on the programmed maximum packet size and transfer size.
•
Reading the receive FIFO
The application must ignore all packet statuses other than IN data packet (bx0010).

Figure 404. Transmit FIFO write task

RM0430 Rev 8
USB on-the-go full-speed (OTG_FS)
1237/1324
1283