NXP Semiconductors MCF5253, Reference Manual

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Universal Serial Bus Interface
MCF5253 Reference Manual, Rev. 1
24-146 Freescale Semiconductor
24.11.5.5 Flushing/De-Priming an Endpoint
It is necessary for the DCD to flush to de-prime one more endpoints on a USB device reset or during a
broken control transfer. There may also be application specific requirements to stop transfers in progress.
The following procedure can be used by the DCD to stop a transfer in progress:
1. Write a '1' to the corresponding bit(s) in ENDPTFLUSH.
2. Wait until all bits in ENDPTFLUSH are '0'.
3. Software note: this operation may take a large amount of time depending on the USB bus activity.
It is not desirable to have this wait loop within an interrupt service routine.
4. Read ENDPTSTATUS to ensure that for all endpoints commanded to be flushed, that the
corresponding bits are now '0'. If the corresponding bits are '1' after step #2 has finished, then the
flush failed as described in the following:
Explanation: In very rare cases, a packet is in progress to the particular endpoint when commanded
flush using ENDPTFLUSH. A safeguard is in place to refuse the flush to ensure that the packet in
progress completes successfully. The DCD may need to repeatedly flush any endpoints that fail to
flush be repeating steps 1-3 until each endpoint is successfully flushed.
24.11.5.6 Device Error Matrix
Table 24-88 summarizes packet errors that are not automatically handled by the USB_DR.
Notice that the device controller handles all errors on Bulk/Control/Interrupt Endpoints except for a data
buffer overflow. However, for ISO endpoints, errors packets are not retried and errors are tagged as
indicated.
Table 24-88. Device Error Matrix
Error Direction
Packet
Type
Data Buffer
Error Bit
Transaction
Error Bit
Overflow ** RX Any 1 0
ISO Packet Error RX ISO 0 1
ISO Fulfillment Error Both ISO 0 1
Table 24-89. Error Descriptions
Error Description
Overflow Number of bytes received exceeded max. packet size or total buffer length.
** This error will also set the Halt bit in the dQH and if there are dTDs remaining in the linked list for the
endpoint, then those will not be executed.
ISO Packet Error CRC Error on received ISO packet. Contents not guaranteed to be correct.
ISO Fulfillment Error Host failed to complete the number of packets defined in the dQH mult field within the given
(micro)frame. For scheduled data delivery the DCD may need to readjust the data queue because a
fulfillment error will cause Device Controller to cease data transfers on the pipe for one (micro)frame.
During the ‘dead’(micro)frame, the Device Controller reports error on the pipe and primes for the
following frame.