USB on-the-go full-speed/high-speed (OTG_FS/OTG_HS) RM0390
1254/1328 RM0390 Rev 4
1. The application must set the transfer size and packet count fields in the endpoint-
specific registers and enable the endpoint to transmit the data.
2. The application must also write the required data to the associated transmit FIFO for
the endpoint.
3. Every time the application writes a packet to the transmit FIFO, the transfer size for that
endpoint is decremented by the packet size. The data are fetched from application
memory until the transfer size for the endpoint becomes 0.
4. When an IN token is received for a periodic endpoint, the core transmits the data in the
FIFO, if available. If the complete data payload (complete packet, in dedicated FIFO
mode) for the frame is not present in the FIFO, then the core generates an IN token
received when Tx FIFO empty interrupt for the endpoint.
– A zero-length data packet is transmitted on the USB for isochronous IN endpoints
– A NAK handshake is transmitted on the USB for interrupt IN endpoints
5. The packet count for the endpoint is decremented by 1 under the following conditions:
– For isochronous endpoints, when a zero- or non-zero-length data packet is
transmitted
– For interrupt endpoints, when an ACK handshake is transmitted
– When the transfer size and packet count are both 0, the transfer completed
interrupt for the endpoint is generated and the endpoint enable is cleared.
6. At the “Periodic frame Interval” (controlled by PFIVL in OTG_DCFG), when the core
finds non-empty any of the isochronous IN endpoint FIFOs scheduled for the current
frame non-empty, the core generates an IISOIXFR interrupt in OTG_GINTSTS.
Application programming sequence:
1. Program the OTG_DIEPCTLx register with the endpoint characteristics and set the
CNAK and EPENA bits.
2. Write the data to be transmitted in the next frame to the transmit FIFO.
3. Asserting the ITTXFE interrupt (in OTG_DIEPINTx) indicates that the application has
not yet written all data to be transmitted to the transmit FIFO.
4. If the interrupt endpoint is already enabled when this interrupt is detected, ignore the
interrupt. If it is not enabled, enable the endpoint so that the data can be transmitted on
the next IN token attempt.
5. Asserting the XFRC interrupt (in OTG_DIEPINTx) with no ITTXFE interrupt in
OTG_DIEPINTx indicates the successful completion of an isochronous IN transfer. A
read to the OTG_DIEPTSIZx register must give transfer size = 0 and packet count = 0,
indicating all data were transmitted on the USB.
6. Asserting the XFRC interrupt (in OTG_DIEPINTx), with or without the ITTXFE interrupt
(in OTG_DIEPINTx), indicates the successful completion of an interrupt IN transfer. A
read to the OTG_DIEPTSIZx register must give transfer size = 0 and packet count = 0,
indicating all data were transmitted on the USB.
7. Asserting the incomplete isochronous IN transfer (IISOIXFR) interrupt in
OTG_GINTSTS with none of the aforementioned interrupts indicates the core did not
receive at least 1 periodic IN token in the current frame.
• Incomplete isochronous IN data transfers
This section describes what the application must do on an incomplete isochronous IN data
transfer.
To Next Page
Loading...
Need help?
General
