RM0385 Datasheet, PDF (1408/1644 Pages) STMicroelectronics – This reference manual targets application developers

USB on-the-go full-speed/high-speed (OTG_FS/OTG_HS)
RM0385
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/OTG_HS host automatically writes an entry (OUT request) to the
periodic/non-periodic request queue, along with the last DWORD 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 DWORDs. If the packet size is non-DWORD
aligned, the application must use padding. The OTG_FS/OTG_HS host determines the
actual packet size based on the programmed maximum packet size and transfer size.
Figure 444. Transmit FIFO write task
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• Reading the receive FIFO
The application must ignore all packet statuses other than IN data packet (bx0010).
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