Figure 534. Receive Fifo Packet Read - ST STM32L4 5 Series Reference Manual

USB on-the-go full-speed (OTG_FS)
SETUP transactions
This section describes how the core handles SETUP packets and the application's
sequence for handling SETUP transactions.
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Application requirements
1. To receive a SETUP packet, the STUPCNT field (OTG_DOEPTSIZx) in a control OUT
endpoint must be programmed to a non-zero value. When the application programs the
STUPCNT field to a non-zero value, the core receives SETUP packets and writes them
to the receive FIFO, irrespective of the NAK status and EPENA bit setting in
OTG_DOEPCTLx. The STUPCNT field is decremented every time the control endpoint
receives a SETUP packet. If the STUPCNT field is not programmed to a proper value
before receiving a SETUP packet, the core still receives the SETUP packet and
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Figure 534. Receive FIFO packet read

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