Western Digital T13/2132-D manual Set Hardware Configuration FN 4Eh

June 23, 2010 T13/2132-D Revision 3

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

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