UM10360 Datasheet, PDF (171/835 Pages) NXP Semiconductors – LPC17xx User manual

NXP Semiconductors
UM10360
Chapter 10: LPC17xx Ethernet
received. The RxConsumeIndex is programmed by software and is the index of the next
descriptor that the software receive driver is going to process. When RxProduceIndex ==
RxConsumeIndex, the receive buffer is empty. When RxProduceIndex ==
RxConsumeIndex -1 (taking wraparound into account), the receive buffer is full and newly
received data would generate an overflow unless the software driver frees up one or more
descriptors.
Each receive descriptor takes two word locations (8 bytes) in memory. Likewise each
status field takes two words (8 bytes) in memory. Each receive descriptor consists of a
pointer to the data buffer for storing receive data (Packet) and a control word (Control).
The Packet field has a zero address offset, the control field has a 4 byte address offset
with respect to the descriptor address as defined in Table 10–174.
Table 174. Receive Descriptor Fields
Symbol
Address Bytes Description
offset
Packet
0x0
4
Base address of the data buffer for storing receive data.
Control
0x4
4
Control information, see Table 10–175.
The data buffer pointer (Packet) is a 32-bit, byte aligned address value containing the
base address of the data buffer. The definition of the control word bits is listed in
Table 10–175.
Table 175. Receive Descriptor Control Word
Bit Symbol
Description
10:0 Size
Size in bytes of the data buffer. This is the size of the buffer reserved by the
device driver for a frame or frame fragment i.e. the byte size of the buffer
pointed to by the Packet field. The size is -1 encoded e.g. if the buffer is 8
bytes the size field should be equal to 7.
30:11 -
Unused
31 Interrupt
If true generate an RxDone interrupt when the data in this frame or frame
fragment and the associated status information has been committed to
memory.
Table 10–176 lists the fields in the receive status elements from the status array.
Table 176. Receive Status Fields
Symbol
Address Bytes Description
offset
StatusInfo
0x0
4
Receive status return flags, see Table 10–178.
StatusHashCRC 0x4
4
The concatenation of the destination address hash CRC and
the source address hash CRC.
Each receive status consists of two words. The StatusHashCRC word contains a
concatenation of the two 9-bit hash CRCs calculated from the destination and source
addresses contained in the received frame. After detecting the destination and source
addresses, StatusHashCRC is calculated once, then held for every fragment of the same
frame.
The concatenation of the two CRCs is shown in Table 10–177:
UM10360_1
User manual
Rev. 01 — 4 January 2010
© NXP B.V. 2010. All rights reserved.
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