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June 23, 2010 T13/2132-D Revision 3
Working Draft Enhanced Disk Drive - 4 (EDD-4) 65
8.26 Set Hardware Configuration (FN 4Eh)
The purpose of this function is to allow non-hardware-specific software to configure host adapter and devices for
optimal operation. ATA channels may have two devices attached, but this function operates on a single-device
basis. This shall be accommodated by the value that is returned in AL. If the host adapter supports the
requested sub-function on a device basis, AL shall be cleared to 00h. If the host adapter only supports the
setting on an ATA channel basis, AL shall be set to 01h. Once this function has been invoked, all subsequent
INT 13h device-access functions shall use the mode specified by this invocation. This means that if "DMA
Maximum" is enabled, INT 13h FN 02h shall read from the device using DMA transfers. The DMA/PIO
selections are mutually exclusive. When "DMA Maximum" is enabled, "PIO Maximum" shall be disabled. If the
requested mode change is not supported this function shall return with CF = 1b and AH = 01h.
Entry
AH 4Eh
AL Hardware configuration sub-function (see table 29)
DL BIOS device number
Exit
Carry Clear Function completed without error
AH Shall be cleared to zero
AL 00h if command was safe, 01h if other devices are affected
Carry Set Function completed with an error
AH Shall be set to the error code
Table 29 — Hardware Configuration Sub-Functions
AL Description
0h Enable prefetch
1h Disable prefetch
2h Set maximum PIO transfer mode.
3h Set PIO mode 0.
4h Return to default PIO transfer mode. Return the system to the PIO mode enabled by the BIOS setup
utility.
5h Enable INT 13h DMA maximum mode. Set the maximum rate allowed by both the host adapter and the
device.
6h Disable INT 13h DMA