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Intel® 460GX Chipset Software Developer’s Manual 10-7
IFB Usage Considerations
NOTE: Timing cycle times are defined by the ATA specification. A device that reports a given DMA mode
capability must be capable of supporting the minimum DMA cycle time.
A drive’s Multi Word DMA or Single Word DMA speed is the fastest Multi Word DMA speed, if
supported, that is supported for the drive. If Multi Word DMA is NOT supported for the reported
timing cycle time then the drive’s best non Ultra DMA speed is based on its Single Word DMA 2
capability.
If N/A is used, the drive is configured for PIO-only. The PIIX mode follows the PIO mode only. If
a drive does not report a DMA cycle time that is consistent with the Target DMA Cycle Time, a
slower speed should be chosen.
The cycle times associated with the various timing modes are defined by the ATA Specification. A
drive that reports a given Multi/Single Word DMA capability must be capable of supporting the
minimum cycle time for that mode.
10.5.5.1 Determining a Drive’s Best PIO Capability
This section describes how to determine a drive’s PIO Capabilities.
The following PIO drive capabilities are supported by the IFB, from fastest to slowest:
• PIO4 w/IORDY
• PIO3 w/IORDY
• PIO2 w/IORDY
• PIO2 (without IORDY)
• Compatible (Drive does not support any of the above PIO Modes.)
Table 10-4. Drive Multi Word DMA/Single Word DMA Capability as a Function of Cycle Time
Drive’s Reported DMA Mode Setting
Drives Reported DMA
Cycle Time
1
Drive’s Best DMA Mode
Multi Word DMA Mode 2 t <= 120ns Multi Word DMA Mode 2
Multi Word DMA Mode 2 120 < t <= 180ns Multi Word DMA Mode 1
Multi Word DMA Mode 2 180 < t <= 240ns Single Word DMA Mode 2
Multi Word DMA Mode 2 t > 240ns N/A (Disabled)
Multi Word DMA Mode 1 t <= 180ns Multi Word DMA Mode 1
Multi Word DMA Mode 1 180 < t <= 240ns Single Word DMA Mode 2
Multi Word DMA Mode 1 t > 240ns N/A (Disabled)
Multi Word DMA Mode 0 N/A N/A (Disabled)
Single Word DMA Mode 2 t <= 240ns Single Word DMA Mode 2
Single Word DMA Mode 2 t > 114ns N/A (Disabled)
Single Word DMA Mode 1 N/A N/A (Disabled)
Single Word DMA Mode 0 N/A N/A (Disabled)
Drive does not support DMA transfers. N/A N/A