Blk   Chr   OCR 

This tells the driver that a block-device file or character device is

being opened or created.

DevReq0dRec

Offset Size Contents

+0      1  bLen         0dH (length of this request packet)

+1      1  bUnitNo      (not used)

+2      1  bCmd         00H (command code)

+3      2  rStatus      OUTPUT: Device Status Word must fill before exit

+5H     8  res          (reserved)

13               size of this record

rStatus  On exit, the driver must place a DevStatusWord here.  Always

set the Done bit (bit 8).  On an error, set the Done bit and

the Error bit (bit 15) and put a Device Error Code in the low

byte.

Notes:   Only drivers capable of device Open/Close-processing need

support this request (see Device Attribute bit 11).

  DOS uses this request whenever an application opens or creates

a file or opens a device (fn 3dH) and DOS issues DvRq 0eH

(Device Close) when the device or file gets closed (fn 3eH).

Drivers supporting this request can uses these fns to help with

maintenance of internal buffers, etc.

Character devices (such as PRN drivers) can watch for Open

requests and send control data to the device (such as font

downloads) when it is opened after being closed.  In that

scenario, the driver should also accept DvRq 03H and DvRq 0cH

(IOCTL fns) in order to provide a means to receive download

data from applications.

See Also: Device Requests

DevRequestHdrRec

Installable Device Drivers

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