IP100A LF
Preliminary Data Sheet
11.2
DMA Data Structures
A TFD is used to move data destined for transmission onto an Ethernet network, from the host system
memory to the transmit FIFO within the IP100A LF. A TFD is 16 to 512 bytes in length, and it’s location in
host system memory is indicated by the value in the TxDMAListPtr register.
A RFD is used to move data obtained from an Ethernet network, from the receive FIFO within the IP100A
LF to the host system memory. A RFD is 16 to 512 bytes in length, and it’s location in host system
memory is indicated by the value in the RxDMAListPtr register. There are two formats for an RFD,
differentiated by the ImpliedBufferEnable bit of the RxFrameStatus field.
Figure 11 shows the two DMA data structures.
HOST SYSTEM MEMORY
TxDMANextPtr
TxFrameControl
TxDMAFragAddr0
TxDMAFragLen0
TxDMAFragAddr1
TxDMAFragLen1
TxDMAFragAddrn
TxDMAFragLenn
TFD
HOST SYSTEM MEMORY
RxDMANextPtr
RxFrameStatus
RxDMAFragAddr0
RxDMAFragLen0
RxDMAFragAddr1
RxDMAFragLen1
RxDMAFragAddrn
RxDMAFragLenn
RFD
Offset from
TFD Start
0x00
0x04
0x08
0x0c
0x10
0x14
0x08+n*0x08
0x0C+n*0x08
Offset from
RFD Start
0x00
0x04
0x08
0x0c
0x10
0x14
0x08+n*0x08
0x0C+n*0x08
FIGURE 11: TFD and RFD DMA Data Structures
11.2.1 RxDMAFragAddr
Class............................. DMA Data Structures, RFD
Base Address ............... Start of RFD
Address Offset .............. 0x08+n*0x08 for nth fragment (where n=0,1,...63)
Access Mode ................ Read/Write
Width ............................ 32 bits
BIT
BIT NAME
BIT DESCRIPTION
31..0
RxDMAFragAddr
Receive DMA Fragment Address. The RxDMAFragAddr contains the
physical address of a contiguous block of system memory to which
receive data is to be transferred by receive DMA. A fragment can start on
any byte boundary.
March. 30, 2007
35/97
Copyright © 2004, IC Plus Corp.
IP100A LF-DS-R17
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