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Chapter 7 - Parameter RAM Utilities / Parameter RAM Utilities Reference

Routines /

WriteParam

You can use the WriteParam function to write the modified values in the system parameters record to parameter RAM.

FUNCTION WriteParam: OSErr;

DESCRIPTION

The WriteParam function writes the modified values in the system parameters record to parameter RAM. Your application should call this function only after making changes to the system parameters record (returned by the GetSysPPtr function described in the previous section).

The WriteParam function also attempts to verify the values written by reading them back in and comparing them to the values in the low-memory copy.

SPECIAL CONSIDERATIONS

Because the organization of parameter RAM is subject to change, you should not use the WriteParam function to change the values in parameter RAM. Instead use the appropriate Toolbox routines to modify values in parameter RAM.

Note

If you accidentally use WriteParam to write incorrect values into parameter RAM, the user can clear the current settings in the parameter RAM and restore the default values by holding down the x-Option-P-R keys at system startup.

ASSEMBLY-LANGUAGE INFORMATION

The registers on entry and exit for the WriteParam functions are

Registers on entry
A0	SysParam
D0	MinusOne

Registers on exit
D0	Result code

For historical reasons, you must set up register A0 with the global variable SysParam and register D0 with the global variable MinusOne. When WriteParam returns, register D0 contains the result code.

RESULT CODES

noErr	0	No error
prWrErr	-87	Parameter RAM written did not verify

SEE ALSO

For a description of the system parameters record, see page 7-31.