OM11077 NXP Semiconductors, OM11077 Datasheet - Page 386

• Manufacturer Part Number: OM11077
• Description: MODULE DIMM LPC2478 ARM7
• Manufacturer: NXP Semiconductors

Specifications of OM11077

• Accessory Type: Module Card
• For Use With/related Products: ARM-57TS-LPC2478
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 568-4742

NXP Semiconductors
15. Double buffered endpoint operation
UM10237_4
User manual
14.7.4 Ending the packet transfer
15.1 Bulk endpoints
The DMA engine proceeds with the transfer until the number of bytes specified in the field
DMA_buffer_length is transferred to or from the USB RAM. Then the EOT interrupt will be
generated. If this happens in the middle of the packet, the linked DD will get loaded and
the remaining part of the packet gets transferred to or from the address pointed by the
new DD.
OUT endpoints
If the linked DD is not valid and the packet is partially transferred to memory, the DD ends
with DataOverrun status code set, and the DMA will be disabled for this endpoint.
Otherwise DD_status will be updated with the NormalCompletion status code.
IN endpoints
If the linked DD is not valid and the packet is partially transferred to USB, the DD ends
with a status code of NormalCompletion in the DD_status field. This situation corresponds
to the end of the USB transfer, and the packet will be sent as a short packet. Also, when
the linked DD is valid and buffer length is 0, an empty packet will be sent to indicate the
end of the USB transfer.
The Bulk and Isochronous endpoints of the USB Device Controller are double buffered to
increase data throughput.
When a double-buffered endpoint is realized, enough space for both endpoint buffers is
automatically allocated in the EP_RAM. See
For the following discussion, the endpoint buffer currently accessible to the CPU or DMA
engine for reading or writing is said to be the active buffer.
For Bulk endpoints, the active endpoint buffer is switched by the SIE Clear Buffer or
Validate Buffer commands.
The following example illustrates how double buffering works for a Bulk OUT endpoint in
Slave mode:
Assume that both buffer 1 (B_1) and buffer 2 (B_2) are empty, and that the active buffer is
B_1.
1. The host sends a data packet to the endpoint. The device hardware puts the packet
2. Software clears the endpoint interrupt and begins reading the packet data from B_1.
3. Software is still reading from B_1 when the host attempts to send a third packet.
4. Software finishes reading the first packet from B_1 and sends a SIE Clear Buffer
into B_1, and generates an endpoint interrupt.
While B_1 is still being read, the host sends a second packet, which device hardware
places in B_2, and generates an endpoint interrupt.
Since both B_1 and B_2 are full, the device hardware responds with a NAK.
command to free B_1 to receive another packet. B_2 becomes the active buffer.
Rev. 04 — 26 August 2009
Chapter 13: LPC24XX USB device controller
Section
13–9.5.1.
UM10237
© NXP B.V. 2009. All rights reserved.
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