82801BA Datasheet, PDF (94/498 Pages) Intel Corporation – Intel 82801BA I/O Controller Hub 2 (ICH2) and Intel 82801BAM I/O Controller Hub 2 Mobile

Functional Description
5.5.2 PCI DMA Expansion Cycles
ICH2’s support of the PC/PCI DMA Protocol currently consists of four types of cycles: Memory-
to-I/O, I/O-to-Memory, Verify, and ISA Master cycles. ISA Masters are supported through the use
of a DMA channel that has been programmed for cascade mode.
The DMA controller does a two cycle transfer (a load followed by a store) as opposed to the ISA
"fly-by" cycle for PC/PCI DMA agents. The memory portion of the cycle generates a PCI memory
read or memory write bus cycle, its address representing the selected memory.
The I/O portion of the DMA cycle generates a PCI I/O cycle to one of four I/O addresses
(Table 5-11). Note that these cycles must be qualified by an active GNT# signal to the requesting
device.
Table 5-11. DMA Cycle vs. I/O Address
DMA Cycle Type
Normal
Normal TC
Verify
Verify TC
DMA I/O Address
00h
04h
0C0h
0C4h
PCI Cycle Type
I/O Read/Write
I/O Read/Write
I/O Read
I/O Read
5.5.3
DMA Addresses
The memory portion of the cycle generates a PCI memory read or memory write bus cycle; its
address representing the selected memory. The I/O portion of the DMA cycle generates a PCI
I/O cycle to one of the four I/O addresses listed in Table 5-11.
5.5.4 DMA Data Generation
The data generated by PC/PCI devices on I/O reads when they have an active GNT# is on the lower
two bytes of the PCI AD bus. Table 5-12 lists the PCI pins that the data appears for 8 and 16 bit
channels. Each I/O read results in one memory write and each memory read results in one I/O
write. If the I/O device is 8 bit, the ICH2 performs an 8 bit memory write. The ICH2 does not
assemble the I/O read into a DWord for writing to memory. Similarly, the ICH2 does not
disassemble a DWord read from memory to the I/O device.
Table 5-12. PCI Data Bus vs. DMA I/O Port Size
PCI DMA I/O Port Size
Byte
Word
PCI Data Bus Connection
AD[7:0]
AD[15:0]
5-32
82801BA ICH2 and 82801BAM ICH2-M Datasheet