UM10375 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
User manual Rev. 3 — 14 June 2011 167 of 368
NXP Semiconductors
UM10375
Chapter 10: LPC13xx USB device controller
6. Software clears the endpoint interrupt. Software fills B_1 with the third packet and
validates it using the SIE Validate Buffer command. The active buffer is switched to
B_2.
7. The device successfully sends the second packet from B_2 and generates an
endpoint interrupt.
8. Software has no more packets to send, so it simply clears the interrupt.
9. The device successfully sends the third packet from B_1 and generates an endpoint
interrupt.
10. Software has no more packets to send, so it simply clears the interrupt.
11. Both B_1 and B_2 are empty, and the active buffer is B_2. The next packet written by
software will go into B_2.
10.14.2 Isochronous endpoints
For isochronous endpoints, the active data buffer is switched by hardware when the
FRAME interrupt occurs. The SIE Clear Buffer and Validate Buffer commands do not
cause the active buffer to be switched.
Double-buffering allows the software to make full use of the frame interval writing or
reading a packet to or from the active buffer, while the packet in the other buffer is being
sent or received on the bus.
For an OUT isochronous endpoint, any data not read from the active buffer before the end
of the frame is lost when it switches.
For an IN isochronous endpoint, if the active buffer is not validated before the end of the
frame, an empty packet is sent on the bus when the active buffer is switched, and its
contents will be overwritten when it becomes active again.
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