Nxp Semiconductors UM10237 User Manual
UM10237_2
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 02 — 19 December 2008
251 of 792
NXP Semiconductors
UM10237
Chapter 11: LPC24XX Ethernet
be written to the TxDescriptorNumber/RxDescriptorNumber registers using a -1 encoding
i.e. the value in the registers is the number of descriptors minus one e.g. if the descriptor
array has 4 descriptors the value of the number of descriptors register should be 3.
i.e. the value in the registers is the number of descriptors minus one e.g. if the descriptor
array has 4 descriptors the value of the number of descriptors register should be 3.
After setting up the descriptor arrays, frame buffers need to be allocated for the receive
descriptors before enabling the receive datapath. The Packet field of the receive
descriptors needs to be filled with the base address of the frame buffer of that descriptor.
Amongst others the Control field in the receive descriptor needs to contain the size of the
data buffer using -1 encoding.
descriptors before enabling the receive datapath. The Packet field of the receive
descriptors needs to be filled with the base address of the frame buffer of that descriptor.
Amongst others the Control field in the receive descriptor needs to contain the size of the
data buffer using -1 encoding.
The receive datapath has a configurable filtering function for discarding/ignoring specific
Ethernet frames. The filtering function should also be configured during initialization.
Ethernet frames. The filtering function should also be configured during initialization.
After an assertion of the hardware reset, the soft reset bit in the MAC will be asserted. The
soft reset condition must be removed before the Ethernet block can be enabled.
soft reset condition must be removed before the Ethernet block can be enabled.
Enabling of the receive function is located in two places. The receive DMA manager
needs to be enabled and the receive datapath of the MAC needs to be enabled. To
prevent overflow in the receive DMA engine the receive DMA engine should be enabled
by setting the RxEnable bit in the Command register before enabling the receive datapath
in the MAC by setting the RECEIVE ENABLE bit in the MAC1 register.
needs to be enabled and the receive datapath of the MAC needs to be enabled. To
prevent overflow in the receive DMA engine the receive DMA engine should be enabled
by setting the RxEnable bit in the Command register before enabling the receive datapath
in the MAC by setting the RECEIVE ENABLE bit in the MAC1 register.
The transmit DMA engine can be enabled at any time by setting the TxEnable bit in the
Command register.
Command register.
Before enabling the datapaths, several options can be programmed in the MAC, such as
automatic flow control, transmit to receive loop-back for verification, full/half duplex
modes, etc.
automatic flow control, transmit to receive loop-back for verification, full/half duplex
modes, etc.
Base addresses of descriptor arrays and descriptor array sizes cannot be modified
without a (soft) reset of the receive and transmit datapaths.
without a (soft) reset of the receive and transmit datapaths.
9.6 Transmit process
Overview
This section outlines the transmission process.
Device driver sets up descriptors and data
If the descriptor array is full the device driver should wait for the descriptor arrays to
become not full before writing to a descriptor in the descriptor array. If the descriptor array
is not full, the device driver should use the descriptor numbered TxProduceIndex of the
array pointed to by TxDescriptor.
become not full before writing to a descriptor in the descriptor array. If the descriptor array
is not full, the device driver should use the descriptor numbered TxProduceIndex of the
array pointed to by TxDescriptor.
The Packet pointer in the descriptor is set to point to a data frame or frame fragment to be
transmitted. The Size field in the Command field of the descriptor should be set to the
number of bytes in the fragment buffer, -1 encoded. Additional control information can be
indicated in the Control field in the descriptor (bits Interrupt, Last, CRC, Pad).
transmitted. The Size field in the Command field of the descriptor should be set to the
number of bytes in the fragment buffer, -1 encoded. Additional control information can be
indicated in the Control field in the descriptor (bits Interrupt, Last, CRC, Pad).
After writing the descriptor the descriptor needs to be handed over to the hardware by
incrementing (and possibly wrapping) the TxProduceIndex register.
incrementing (and possibly wrapping) the TxProduceIndex register.
If the transmit datapath is disabled, the device driver should not forget to enable the
transmit datapath by setting the TxEnable bit in the Command register.
transmit datapath by setting the TxEnable bit in the Command register.