Int 15H [AT] [PS/2] Function 90H (144) Device wait

Invoked by the ROM BIOS fixed disk, floppy disk, printer, network, and keyboard drivers prior to performing a programmed wait for I/O completion.

Call with:

AH = 90H

AL = device type

00H—7FH serially reusable devices

80H—BFH reentrant devices

C0H—FFH wait-only calls, no corresponding Post function

ES:BX = segment:offset of request block for device types 80H—FFH

Returns:

If no wait (driver must perform its own time-out)

Carry flag = clear

AH = 00H

If wait was performed

Carry flag = set

Notes:

Predefined device types are:

00H disk (may time-out) 01H floppy disk (may time-out) 02H keyboard (no time-out) 03H pointing device (PS/2, may time-out) 80H network (no time-out) FCH fixed disk reset (PS/2, may time-out) FDH floppy disk drive motor start (may time-out) FEH printer (may time-out)

For network adapters, ES:BX points to a network control block (NCB).

A multitasking program manager would be expected to capture Int 15H Function 90H so that it can dispatch other tasks while I/O is in progress. The default BIOS routine for this function simply returns with the carry flag clear and AH = 00H.