DocID018909 Rev 11
RM0090
USB on-the-go high-speed (OTG_HS)
1529
channel and wait for a channel halted interrupt. The application must be able to receive
other interrupts (DTERR, NAK, Data, TXERR) for the same channel before receiving
the halt.
3. When a DISCINT (Disconnect Device) interrupt in OTG_HS_GINTSTS is received.
(The application is expected to disable all enabled channels
4. When the application aborts a transfer before normal completion.
Ping protocol
When the OTG_HS host operates in high speed, the application must initiate the ping
protocol when communicating with high-speed bulk or control (data and status stage) OUT
endpoints.
The application must initiate the ping protocol when it receives a NAK/NYET/TXERR
interrupt. When the HS_OTG host receives one of the above responses, it does not
continue any transaction for a specific endpoint, drops all posted or fetched OUT requests
(from the request queue), and flushes the corresponding data (from the transmit FIFO).
This is valid in slave mode only. In Slave mode, the application can send a ping token either
by setting the DOPING bit in HCTSIZx before enabling the channel or by just writing the
HCTSIZx register with the DOPING bit set when the channel is already enabled. This
enables the HS_OTG host to write a ping request entry to the request queue. The
application must wait for the response to the ping token (a NAK, ACK, or TXERR interrupt)
before continuing the transaction or sending another ping token. The application can
continue the data transaction only after receiving an ACK from the OUT endpoint for the
requested ping. In DMA mode operation, the application does not need to set the DOPING
bit in HCTSIZx for a NAK/NYET response in case of Bulk/Control OUT. The OTG_HS host
automatically sets the DOPING bit in HCTSIZx, and issues the ping tokens for Bulk/Control
OUT. The HS_OTG host continues sending ping tokens until it receives an ACK, and then
switches automatically to the data transaction.
Operational model
The application must initialize a channel before communicating to the connected device.
This section explains the sequence of operation to be performed for different types of USB
transactions.
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Writing the transmit FIFO
The OTG_HS host automatically writes an entry (OUT request) to the periodic/nonperiodic
request queue, along with the last DWORD write of a packet. The application must ensure
that at least one free space is available in the periodic/nonperiodic request queue before
starting to write to the transmit FIFO. The application must always write to the transmit FIFO
in DWORDs. If the packet size is nonDWORD aligned, the application must use padding.
The OTG_HS host determines the actual packet size based on the programmed maximum
packet size and transfer size.
