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IFB Usage Considerations
10-12 Intel® 460GX Chipset Software Developer’s Manual
Refer to the Set Features Command description in the ATA Specification for more information.
A drive may only be enabled for a Single DMA capability. In general, if a drive supports a
supported Ultra DMA speed, then Ultra DMA is configured for the drive. If a drive does not
support Ultra DMA, then it should be configured with it’s selected DMA speed, if it exists. If a
drive supports only PIO (does not have support for either Ultra DMA or DMA speeds), then the
drive shall only be accessed in a PIO mode only.
If a drive is configured for an Ultra DMA speed or a DMA speed, its corresponding DMA-capable
bit in the PCI Bus Master I/O Status Register (Primary: PCI Bus Master IDE I/O Offset + 02h;
Secondary - PCI Bus Master I/O Offset + 0Ah) MUST be set. This will allow PCI Bus Master IDE
capable device drivers to recognize the fact that this drive has been identified and configured by the
firmware for PCI Bus Master IDE operation.
Table 10-11. Ultra DMA/Multi Word DMA/Single Word Transfer/Mode Values
Drive’s Selected Ultra
DMA Capability
Drive’s Selected Non-
ultra DMA Capability
Selected Speed
ATA SET_FEATURES -
Command Set Transfer
Mode Sub Command
Parameter for Selected
Speed
Ultra DMA Mode 2 any Ultra DMA Mode 2 42h
Ultra DMA Mode 1 any Ultra DMA Mode 1 41h
Ultra DMA Mode 0 any Ultra DMA Mode 0 40h
N/A Multi Word DMA Mode 2 Multi Word DMA Mode 2 22h
N/A Multi Word DMA Mode 1 Multi Word DMA Mode 1 21h
N/A Single Word DMA Mode
2
Single Word DMA Mode
2
12h
N/A N/A Disabled N/A
Table 10-12. PIO Transfer/Mode Values
Drive’s Selected PIO Speed Capability
ATA SET_FEATURES -Command Set Transfer Mode
Sub Command Parameter for Selected Speed
PIO0/PIO1/PIO2/Compatible N/A
PIO3 w/IORDY Flow Control C3
PIO4 w/IORDY Flow Control C4