NXP Semiconductors LPC24XX UM10237 - Manual (Page 232)

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User manual Rev. 04 — 26 August 2009 232 of 792
NXP Semiconductors
UM10237
Chapter 11: LPC24XX Ethernet
The transmit status 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 statuses.
7.2.10 Transmit Number of Descriptors Register (TxDescriptorNumber -
0xFFE0 0124)
The Transmit Number of Descriptors register (TxDescriptorNumber) has an address of
0xFFE0 0124. Its bit definition is shown in
Table 11–215 .
The transmit number of descriptors register defines the number of descriptors in the
descriptor array for which TxDescriptor is the base address. The number of descriptors
should match the number of statuses. The register uses minus one encoding i.e. if the
array has 8 elements, the value in the register should be 7.
7.2.11 Transmit Produce Index Register (TxProduceIndex - 0xFFE0 0128)
The Transmit Produce Index register (TxProduceIndex) has an address of 0xFFE0 0128.
Its bit definition is shown in
Table 11–216 .
The transmit produce index register defines the descriptor that is going to be filled next by
the software transmit driver. The transmit descriptor array is empty as long as
TxProduceIndex equals TxConsumeIndex. If the transmit hardware is enabled, it will start
transmitting frames as soon as the descriptor array is not empty. After a frame has been
processed by software, it should increment the TxProduceIndex. The value must be
wrapped to 0 once the value of TxDescriptorNumber has been reached. If the
TxProduceIndex equals TxConsumeIndex - 1 the descriptor array is full and software
should stop producing new descriptors until hardware has transmitted some frames and
updated the TxConsumeIndex.
Table 214. Transmit Status Base Address register (TxStatus - address 0xFFE0 0120) bit
description
Bit Symbol Function Reset
value
1:0 - Fixed to ’00’ -
31:2 TxStatus MSBs of transmit status base address. 0x0
Table 215. Transmit Number of Descriptors register (TxDescriptorNumber - address
0xFFE0 0124) bit description
Bit Symbol Function Reset
value
15:0 TxDescriptorNumber Number of descriptors in the descriptor array for which
TxDescriptor is the base address. The register is minus
one encoded.
31:16 - Unused 0x0
Table 216. Transmit Produce Index register (TxProduceIndex - address 0xFFE0 0128) bit
description
Bit Symbol Function Reset
value
15:0 TxProduceIndex Index of the descriptor that is going to be filled next by the
transmit software driver. 0x0
31:16 - Unused 0x0