w83c553f Winbond Electronics Corp America, w83c553f Datasheet - Page 92

• Manufacturer Part Number: w83c553f
• Description: System I/o Controller With Pci Arbiter
• Manufacturer: Winbond Electronics Corp America

W83C553F
Electrical Specifications
Scatter/Gather Registers
Scatter/Gather (S/G) provides the capability of transferring multiple buffers between memory (ISA/PCI) and I/O (ISA DMA
device) without CPU intervention. In Scatter/Gather the DMA can read the memory address and word count from an array of
buffer descriptors located in system memory (PCI only), called the Scatter/Gather Descriptor (SCD) table. This allows the
DMA controller to sustain DMA transfers until all of the buffers in the SGD table are transferred.
Software prepares a SGD table in system memory. Each SGD is 8-bytes long and consists of an address pointer to the
starting address and the byte count (number of bytes) of the memory buffer to be transferred. In any given SGD table, two
consecutive SGDs are offset by 8-bytes and are aligned on a 4-byte boundary. Each SGD is defined below. For an 8-bit
DMA I/O device:
For a 16-bit DMA I/O device, bit 0 of the Memory Buffer Starting Address and byte count must be 0.
Bit 31 of Dword 1 is the end of Link Flag. Bus master operation terminates upon completion of the description entry that has
EOL set.
The SGD table cannot cross a 64k memory boundary.
The addresses of all of the registers located from 43Fh to 40Ah (except 40Bh) are relocatable by programming the
Scatter/Gather Relocation Base Address Register (Function 0, address 41h) in the PCI Configuration Space. These registers
are marked with an asterisk (*).
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