; C02 Module dirent Assembly Language Eoutines for run6502 emulator
; This is the reference implementation of the dirent module 
; Requires external functions FSADDR, FSCMD, and FSDRVN (fileio.h02)

        SUBROUTINE DIRENT

;opndir() - Open Directory for Reading
;Args: A = Drive Identifier
;      Y,X = Pointer to Directory Name
;Returns: A = File Pointer (0 = Not Opened)
;         Y = Error Code (0 = None)
OPNDIR: JSR FSDRVN        ;Convert Drive Letter to Drive Number
        BCS .OPNERR       ;If Invalid Return Error
        LDA #'D'          ;Set Command to OPENDIR
.FSCMDX JSR FSCMD         ;Execute Command
        TXA               ;Return Channel
        RTS

.OPNERR LDA #0              ;Directory Not Opened
        RTS

;rdhdr() - Read Directory Header
;Note: Call once before first readdir
;Args: A = Directory File Pointer
;      Y,X = Pointer to HDRENT buffer
;Returns: A = Length of Header (0=None)
;         Y = Error Code (0=None)
RDHDR:  SEC         ;Set Mode to HEADER
        BCS .RDDIR  ;Execute READDIR

;rddir() - Read Directory Entry
;Args: A = Directory File Pointer
;      Y,X = Pointer to dirent structure 
;Returns: A = Length of Entry (0=None)
;         Y = Error Cooe (0=None)
RDDIR:  CLC         ;Set Mode to ENTRY
.RDDIR  JSR FSADDR  ;Save Address
        TAY         ;Set Channel
        LDA #'J'    ;Set Command to READDIR
        BNE .FSCMDX ;Execute and Return Result

;clsdir() - Close Directory File
;Args: A = Directory File Pointer
;Returns: A = Error Code (0 = Success)
CLSDIR: TAY         ;Set Channel
        LDA #'B'    ;Set Command to CLOSEDIR
        JSR FSCMD   ;Execute Command
        TYA         ;and Return Error Code
        RTS