Sundance Spas ST201 - Manual (Page 27)

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Sundance Technology ST201 PRELIMINARY draft 2
REGISTERS AND DATA STRUCTURES
DMA DATA STRUCTURES
A TFD is used to move data, which is to be transmitted onto a LAN, from host system memory to the
TxFIFO within the ST201. 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, which has been received from a LAN, from the RxFIFO within the ST201 to
host system memory. A RFD is 16 to 512 bytes in length, and it’s location in host system memory is indi-
cated by the value in the RxDMAListPtr register.
Figure 9 shows the two DMA data structures.
0x00
0x04
0x08
0x0c
0x10
0x14
0x00+n · 8
0x04+n · 8
Next TFD Ptr.
TxFrameControl
1st TxDMAFragAddr
1st TxDMAFragLen
2nd TxDMAFragAddr
2nd TxDMAFragLen
nth TxDMAFragAddr
nth TxDMAFragLen
HOST SYSTEM MEMORY
TFD
FIGURE 9: TFD and RFD DMA Data Structures
Offset from
TFD Start
0x00
0x04
0x08
0x0c
0x10
0x14
0x00+n · 8
0x04+n · 8
Next RFD Ptr.
RxFrameStatus
1st RxDMAFragAddr
1st RxDMAFragLen
2nd RxDMAFragAddr
2nd RxDMAFragLen
nth RxDMAFragAddr
nth RxDMAFragLen
HOST SYSTEM MEMORY
RFD
Offset from
RFD Start