IFB Usage Considerations

Software at this stage needs to determine if at least one of the above modes is supported by the drive. Software should initially determine a drive’s best PIO w/IORDY capability (PIO4 w/IORDY or PIO3 w/IORDY) initially. If these PIO w/IORDY modes are not supported, the drive should determine the PIO2 mode support with IORDY or PIO2 mode support without IORDY. Otherwise, Compatible timings should be applied to the drive.

The drive’s PIO w/IORDY mode capability is specified in the IDENTIFY_DRIVE buffer, Words 64 and 68. Software must first check to see that the Words 64-70 are valid before determining the drive’s PIO w/IORDY drive capability.

The drive’s PIO2 mode capability and current configuration are specified in the

IDENTIFY_DRIVE buffer, Word 51.

Table 10-5. Identify Device Information Used for Determining PIO Drive Capabilities

Capability

Word Offset

Bits

Field

 

 

 

 

PIO

51

15:8

PIO Data Transfer Cycle Timing Mode Supported

 

 

 

00h: PIO0

 

 

 

01h: PIO1

 

 

 

02h: PIO2

 

 

 

 

PIO, DMA

53

1

Field Validity

 

 

 

0: the fields reported in words 64-70 are not valid

 

 

 

1: the fields reported in word 64-70 are valid

 

 

 

 

PIO

64

7:0

Advanced Flow Control PIO Transfer Modes Supported

 

 

 

bit 0: PIO3 (w/IORDY Flow Control)

 

 

 

bit 1: PIO4 (w/IORDY Flow Control)

 

 

 

 

PIO

68

15:0

Minimum PIO Transfer Cycle Time with IORDY Flow Control

 

 

 

 

To determine the drive’s best PIO capability ensure that the drive reports the capability and is able to transfer at the target cycle time:

Table 10-6. Drive PIO Capability as a Function of Cycle Time

Drive’s Reported PIO Mode Setting

Drives Reported PIO

Drive’s Best PIO Mode

Cycle Time

 

 

 

 

 

PIO4

t <= 120ns

PIO4

 

 

 

PIO4

120 < t <= 180ns

PIO3

 

 

 

PIO4

180 < t <= 240ns

PIO2

 

 

 

PIO4

t > 240ns

PIO0/Compatible

 

 

 

PIO3

t <= 180ns

PIO3

 

 

 

PIO3

180 < t <= 240ns

PIO2

 

 

 

PIO3

t > 240ns

PIO0/Compatible

 

 

 

PIO2

N/A (drive must support t<= 240ns)

PIO2

 

 

 

PIO1

N/A

PIO0/Compatible

 

 

 

PIO0/Compatible

N/A

PIO0/Compatible

 

 

 

Note: The cycle times associated with the various timing modes are defined by the ATA Specification. A drive that reports a given PIO capability must be capable of supporting the minimum cycle time for that mode.

Note: If a drive does not report a PIO cycle time that is consistent with the Target PIO Cycle Time, a slower speed should be chosen.

10-8

Intel® 460GX Chipset Software Developer’s Manual