RM0033 Rev 9 1077/1381
RM0033 USB on-the-go full-speed (OTG_FS)
1097
Sequence of operations:
1. Enable all OUT endpoints by setting
– EPENA = 1 in all OTG_FS_DOEPCTLx registers.
2. Flush the RxFIFO as follows
– Poll OTG_FS_GRSTCTL.AHBIDL until it is 1. This indicates that AHB master is
idle.
– Perform read modify write operation on OTG_FS_GRSTCTL.RXFFLSH =1
– Poll OTG_FS_GRSTCTL.RXFFLSH until it is 0, but also using a timeout of less
than 10 milli-seconds (corresponds to minimum reset signaling duration). If 0 is
seen before the timeout, then the RxFIFO flush is successful. If at the moment the
timeout occurs, there is still a 1, (this may be due to a packet on EP0 coming from
the host) then go back (once only) to the previous step (“Perform read modify write
operation”).
3. Before disabling any OUT endpoint, the application must enable Global OUT NAK
mode in the core, according to the instructions in “Setting the global OUT NAK on
page 1075”. This ensures that data in the RxFIFO is sent to the application
successfully. Set SGONAK = 1 in OTG_FS_DCTL
4. Wait for the GONAKEFF interrupt (OTG_FS_GINTSTS)
5. Disable all active OUT endpoints by programming the following register bits:
– EPDIS = 1 in registers OTG_FS_DOEPCTLx
– SNAK = 1 in registers OTG_FS_DOEPCTLx
6. Wait for the EPDIS interrupt in OTG_FS_DOEPINTx for each OUT endpoint
programmed in the previous step. The EPDIS interrupt in OTG_FS_DOEPINTx
indicates that the corresponding OUT endpoint is completely disabled. When the
EPDIS interrupt is asserted, the following bits are cleared:
– EPENA = 0 in registers OTG_FS_DOEPCTLx
– EPDIS = 0 in registers OTG_FS_DOEPCTLx
– SNAK = 0 in registers OTG_FS_DOEPCTLx
• Generic non-isochronous OUT data transfers
This section describes a regular non-isochronous OUT data transfer (control, bulk, or
interrupt).
Application requirements
1. Before setting up an OUT transfer, the application must allocate a buffer in the memory
to accommodate all data to be received as part of the OUT transfer.
2. For OUT transfers, the transfer size field in the endpoint’s transfer size register must be
a multiple of the maximum packet size of the endpoint, adjusted to the word boundary.
– transfer size[EPNUM] = n × (MPSIZ[EPNUM] + 4 – (MPSIZ[EPNUM] mod 4))
– packet count[EPNUM] = n
– n > 0
3. On any OUT endpoint interrupt, the application must read the endpoint’s transfer size
register to calculate the size of the payload in the memory. The received payload size
can be less than the programmed transfer size.
– Payload size in memory = application programmed initial transfer size – core
updated final transfer size
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