RM0390 Rev 4 1241/1328
RM0390 USB on-the-go full-speed/high-speed (OTG_FS/OTG_HS)
1264
Figure 424. Receive FIFO packet read
SETUP transactions
This section describes how the core handles SETUP packets and the application’s
sequence for handling SETUP transactions.
• 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
decrements the STUPCNT field, but the application may not be able to determine the
correct number of SETUP packets received in the setup stage of a control transfer.
– STUPCNT = 3 in OTG_DOEPTSIZx
2. The application must always allocate some extra space in the receive data FIFO, to be
able to receive up to three SETUP packets on a control endpoint.
– The space to be reserved is 10 words. Three words are required for the first
SETUP packet, 1 word is required for the setup stage done word and 6 words are
required to store two extra SETUP packets among all control endpoints.
– 3 words per SETUP packet are required to store 8 bytes of SETUP data and 4
bytes of SETUP status (setup packet pattern). The core reserves this space in the
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