This Technical Note shows how to clear the "backup needed bit" in a directory entry's access byte.
If you are writing a file backup utility program, you probably want to clear the backup needed bit in each directory entry's access byte as you make the backup of the file associated with that directory entry. The SET_FILE_INFO MLI call normally sets the backup needed bit of the access byte, but how do you clear it? The answer is at location BUBIT ($BF95) on the ProDOSĘ8 system global page.
BUBIT normally contains the value $00. When BUBIT contains $00, the SET_FILE_INFO MLI call always sets the backup needed bit in the directory entry's access byte. However, if the value $20 is stored in BUBIT immediately before calling SET_FILE_INFO, the backup needed bit in the directory entry's access byte can be cleared. BUBIT is set back to $00 by the MLI call. The following code example shows how to clear the backup needed bit. Values other than $20 or $00 in BUBIT are not supported.
; The pathname of the file should be in ThePathname buffer when this code is called! 65816 off longa off longi off ClearBackupBit start ; System global page locations MLI equ $BF00 ;MLI call entry point BUBIT equ $BF95 ;Backup Bit Disable, SET_FILE_INFO only ; MLI call numbers SET_FILE_INFO equ $C3 GET_FILE_INFO equ $C4 ; set up FileInfoParms for GET_FILE_INFO MLI call lda #$0A sta param_count ; then... jsr MLI ;get the current file info dc I1'GET_FILE_INFO' dc I2'FileInfoParms' bne Error lda #$20 ;set the backup bit disable bit sta BUBIT eor #$FF and access ;clear the backup needed bit sta access ; set up FileInfoParms for SET_FILE_INFO MLI call lda #$07 sta param_count ; then... jsr MLI ;set the file info with the file info dc I1'SET_FILE_INFO' ;(clearing only the backup needed bit) dc I2'FileInfoParms' bne Error rts ;return to caller Error anop ;routine to handle MLI errors rts ; Parameter block used for GET_FILE_INFO and SET_FILE_INFO MLI calls FileInfoParms anop param_count ds 1 pathname dc i2'ThePathname' access ds 1 file_type ds 1 aux_type ds 2 storage_type ds 1 blocks_used ds 2 mod_date ds 2 mod_time ds 2 create_date ds 2 create_time ds 2 ThePathname entry ds 65 ;store the pathname of the file here end
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