Content Comparison

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NOTE: In the following descriptions the ASCII character corresponding to a hexadecimal value is sometimes placed next to it within brackets. This is done to indicate the mnemonic nature of the values used. For example ($4E,"N") represents the single hexadecimal value $4E, the "N" is mnemonic for DT_NAM, the name record type. 

Major types 

DM_RAMDEV ($81)            RAM device (internal use only)

DM_DEVCHD ($82)            Character Device (pseudo type, internal use only)
                        (SCR.0, PRT.0, COM.0, NUL.0, INP.0, OUT.0)
DM_ROM ($83)            ROM Information, consists of three record types:
                        DT_INF ($40,"@")        application information
                        DT_HLP ($48,"H")        help information
                                               DT_NAM ($4E,"N")               name of application
DM_EPR ($84)            EPR device (eprom file area)

NOTE: It is not possible to add external device drivers to the system via a DOR, despite the major types shown above. This is because device drivers are not integrated into the DOR system. 
 

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DORs are manipulated using the OS_Dor call, which is supplied with various reason codes, one for each DOR operation. The possible operations are:

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RST 20H, DEFB $87

In:

            A = reason code
            HL, IX arguments
            Other register usage depends on reason code

 Out, if call successful:

            Fc = 0
            returned values depend on A(in)

 Out, if call failed:

            Fc = 1
            A = error code:
                        RC_BAD ($04), bad arguments
                        RC_HAND ($08), bad handle
                        RC_ROOM ($07), no room
                        RC_EOF ($09), end of file

Each reason code operation action is described in detail with the OS_Dor call in the "System Calls Reference" section. 

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The following example reads the last updated date of a file, which can only be done by reading the DOR of the file. To get a DOR handle for a file, the user must use the GN_Opf call with A = OP_DOR ($06). This differs from the other options of GN_Opf in that:

1) It does not open the file. 2) It returns a DOR handle rather than a file handle

Note that the file should be closed before the call is made, and that it is necessary to free the DOR handle after you have finished, by using OS_Dor with reason code DR_FRE.

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