Worst Case Response Time - ST STM32L4x6 Reference Manual

USB on-the-go full-speed (OTG_FS)
core has disabled the endpoint.
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• Stalling non-isochronous IN endpoints
This section describes how the application can stall a non-isochronous endpoint.
Application programming sequence:
1. Disable the IN endpoint to be stalled. Set the STALL bit as well.
2. EPDIS = 1 in OTG_DIEPCTLx, when the endpoint is already enabled
–
–
3. Assertion of the Endpoint Disabled interrupt (in OTG_DIEPINTx) indicates to the
application that the core has disabled the specified endpoint.
4. The application must flush the non-periodic or periodic transmit FIFO, depending on
the endpoint type. In case of a non-periodic endpoint, the application must re-enable
the other non-periodic endpoints that do not need to be stalled, to transmit data.
5. Whenever the application is ready to end the STALL handshake for the endpoint, the
STALL bit must be cleared in OTG_DIEPCTLx.
6. If the application sets or clears a STALL bit for an endpoint due to a
SetFeature.Endpoint Halt command or ClearFeature.Endpoint Halt command, the
STALL bit must be set or cleared before the application sets up the Status stage
transfer on the control endpoint.
Special case: stalling the control OUT endpoint
The core must stall IN/OUT tokens if, during the data stage of a control transfer, the host
sends more IN/OUT tokens than are specified in the SETUP packet. In this case, the
application must enable the ITTXFE interrupt in OTG_DIEPINTx and the OTEPDIS interrupt
in OTG_DOEPINTx during the data stage of the control transfer, after the core has
transferred the amount of data specified in the SETUP packet. Then, when the application
receives this interrupt, it must set the STALL bit in the corresponding endpoint control
register, and clear this interrupt.
43.16.6

Worst case response time

When the OTG_FS controller acts as a device, there is a worst case response time for any
tokens that follow an isochronous OUT. This worst case response time depends on the AHB
clock frequency.
The core registers are in the AHB domain, and the core does not accept another token
before updating these register values. The worst case is for any token following an
isochronous OUT, because for an isochronous transaction, there is no handshake and the
next token could come sooner. This worst case value is 7 PHY clocks when the AHB clock
is the same as the PHY clock. When the AHB clock is faster, this value is smaller.
If this worst case condition occurs, the core responds to bulk/interrupt tokens with a NAK
and drops isochronous and SETUP tokens. The host interprets this as a timeout condition
for SETUP and retries the SETUP packet. For isochronous transfers, the Incomplete
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At this point, the application must flush the data in the associated transmit FIFO or
overwrite the existing data in the FIFO by enabling the endpoint for a new transfer
in the next microframe. To flush the data, the application must use the
OTG_GRSTCTL register.
STALL = 1 in OTG_DIEPCTLx
The STALL bit always takes precedence over the NAK bit
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