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Universal Serial Bus Interface – On-The-Go Module
Overflow
ISO Packet Error
ISO Fulfillment Error
10.5.4
Servicing Interrupts
The interrupt service routine must understand there are high frequency, low frequency, and error
operations to order accordingly.
10.5.4.1
High Frequency Interrupts
In particular, high frequency interrupts must be managed in the order below. The most important of these
is listed first because the DCD must acknowledge a setup buffer in the timeliest manner possible.
Execution
Interrupt
Order
1a
USB Interrupt
EPSETUPSR
1b
USB Interrupt
EPCOMPLETE
2
SOF Interrupt
1
It is likely multiple interrupts stack up on any call to the interrupt service routine and during interrupt service routine.
10.5.4.1.1
Low Frequency Interrupts
The low frequency events include the following interrupts. These interrupts can be managed in any order
because they do not occur often in comparison to the high-frequency interrupts.
Interrupt
Port Change
Sleep Enable (Suspend)
Reset Received
10-74
Table 10-59. Error Descriptions
Number of bytes received exceeded max. packet size or total buffer length.
Note: This error also sets the halt bit in the dQH, and if there are dTDs remaining in the
linked list for the endpoint, those are not executed.
CRC error on received ISO packet. Contents not guaranteed correct.
Host failed to complete the number of packets defined in the dQH mult field within the given
(micro)frame. For scheduled data delivery, DCD may need to readjust the data queue
because a fulfillment error causes the 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.
Table 10-60. Interrupt Managing Order
1
Copy contents of setup buffer and acknowledge setup packet (as indicated
in
Section 10.5.3.5, "Managing Queue
according to USB specification chapter 9 or application specific protocol.
Manage completion of dTD as indicated in
Queue Heads."
Action as deemed necessary by application. This interrupt may not have a
use in all applications.
Table 10-61. Low Frequency Interrupt Events
Change software state information.
Change software state information. Low power managing as
necessary.
Change software state information. Abort pending transfers.
Action
Heads"). Process setup packet
Section 10.5.3.5, "Managing
Action
Freescale Semiconductor
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