USB on-the-go full-speed (OTG_FS) RM0090
1113/1422 Doc ID 018909 Rev 4
30.17 OTG_FS programming model
30.17.1 Core initialization
The application must perform the core initialization sequence. If the cable is connected
during power-up, the current mode of operation bit in the OTG_FS_GINTSTS (CMOD bit in
OTG_FS_GINTSTS) reflects the mode. The OTG_FS controller enters host mode when an
“A” plug is connected or device mode when a “B” plug is connected.
This section explains the initialization of the OTG_FS controller after power-on. The
application must follow the initialization sequence irrespective of host or device mode
operation. All core global registers are initialized according to the core’s configuration:
1. Program the following fields in the OTG_FS_GAHBCFG register:
– Global interrupt mask bit GINTMSK = 1
– RxFIFO non-empty (RXFLVL bit in OTG_FS_GINTSTS)
– Periodic TxFIFO empty level
2. Program the following fields in the OTG_FS_GUSBCFG register:
– HNP capable bit
– SRP capable bit
– FS timeout calibration field
– USB turnaround time field
3. The software must unmask the following bits in the OTG_FS_GINTMSK register:
OTG interrupt mask
Mode mismatch interrupt mask
4. The software can read the CMOD bit in OTG_FS_GINTSTS to determine whether the
OTG_FS controller is operating in host or device mode.
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