NXP Semiconductors LPC24XX UM10237 - Manual (Page 231)

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User manual Rev. 04 — 26 August 2009 231 of 792
NXP Semiconductors
UM10237
Chapter 11: LPC24XX Ethernet
The receive produce index register defines the descriptor that is going to be filled next by
the hardware receive process. After a frame has been received, hardware increments the
index. The value is wrapped to 0 once the value of RxDescriptorNumber has been
reached. If the RxProduceIndex equals RxConsumeIndex - 1, the array is full and any
further frames being received will cause a buffer overrun error.
7.2.7 Receive Consume Index Register (RxConsumeIndex - 0xFFE0 0118)
The Receive consume index register (RxConsumeIndex) has an address of
0xFFE0 0118. Its bit definition is shown in
Table 11–212 .
The receive consume register defines the descriptor that is going to be processed next by
the software receive driver. The receive array is empty as long as RxProduceIndex equals
RxConsumeIndex. As soon as the array is not empty, software can process the frame
pointed to by RxConsumeIndex. After a frame has been processed by software, software
should increment the RxConsumeIndex. The value must be wrapped to 0 once the value
of RxDescriptorNumber has been reached. If the RxProduceIndex equals
RxConsumeIndex - 1, the array is full and any further frames being received will cause a
buffer overrun error.
7.2.8 Transmit Descriptor Base Address Register (TxDescriptor - 0xFFE0 011C)
The Transmit Descriptor base address register (TxDescriptor) has an address of
0xFFE0 011C. Its bit definition is shown in
Table 11–213 .
The transmit descriptor base address is a byte address aligned to a word boundary i.e.
LSB 1:0 are fixed to ’00’. The register contains the lowest address in the array of
descriptors.
7.2.9 Transmit Status Base Address Register (TxStatus - 0xFFE0 0120)
The Transmit Status base address register (TxStatus) has an address of 0xFFE0 0120. Its
bit definition is shown in
Table 11–214 .
Table 212. Receive Consume Index register (RXConsumeIndex - address 0xFFE0 0118) bit
description
Bit Symbol Function Reset
value
15:0 RxConsumeIndex Index of the descriptor that is going to be processed next by
the receive
31:16 - Unused 0x0
Table 213. Transmit Descriptor Base Address register (TxDescriptor - address 0xFFE0 011C)
bit description
Bit Symbol Function Reset
value
1:0 - Fixed to ’00’ -
31:2 TxDescriptor MSBs of transmit descriptor base address. 0x0