Loader: LoadFile

       Name: LoadFile                                                [Show more]
       Type: Subroutine
   Category: Loader
    Summary: Load a multi-sector file
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * Elite loader calls LoadFile


.LoadFile

 LDA #12                ; Set tslIndex = 12, so we can use this as an index into
 STA tslIndex           ; the track/sector list for the file we want to load,
                        ; starting with the index of the first track/sector pair
                        ; in byte #12

 JSR findf              ; Search the disk catalog for a file with the filename
                        ; in comnam

 BCS load4              ; If no file is found with this name then findf will
                        ; set the C flag, so jump to load4 to return from the
                        ; subroutine as the file cannot be found

 JSR gettsl             ; Get the track/sector list of the file and populate the
                        ; track and sector variables with the track and sector
                        ; of the file's contents, to pass to the call to rsect

 JSR CopyTrackSector    ; Copy the track/sector list from the buffer into
                        ; trackSector so we can work our way through it to load
                        ; the file one sector at a time

.load1

 JSR rsect              ; Read the first sector of the file's data into the
                        ; buffer (or the next sector if we loop back from below)

 LDY skipBytes          ; Set Y to the number of bytes to skip from the start of
                        ; the file, so we can use it as a starting index into
                        ; the first sector that we copy

 LDX #0                 ; Set X = 0 to act as a byte index into the destination
                        ; address for the file

.load2

 LDA buffer,Y           ; Set A to the Y-th byte in the buffer

.loadAddr

 STA $4000,X            ; And copy it to the X-th byte of the load address,
                        ; which by this point has been modified to the correct
                        ; load address by the SetLoadVariables1 or
                        ; SetLoadVariables2 routine

 JSR DecrementFileSize  ; Decrement the file size in fileSize(1 0) by 1 as we
                        ; have just loaded one more byte of the file

 BMI load4              ; If the result is negative then we have copied all
                        ; fileSize(1 0) bytes, so jump to load4 to return from
                        ; the subroutine

 INX                    ; Increment the destination index in X

 INY                    ; Increment the source index in Y

 BNE load2              ; Loop back until we have reached the end of the page
                        ; page in the source index

 INC loadAddr+2         ; Update the load address as follows:
 LDA loadAddr+1         ;
 SEC                    ;   loadAddr = loadAddr + 256 - skipBytes
 SBC skipBytes          ;
 STA loadAddr+1         ; This makes sure that loadAddr points to the correct
 LDA loadAddr+2         ; load address for the next sector, as we just loaded a
 SBC #0                 ; sector's worth of bytes (256) and skipped the first
 STA loadAddr+2         ; skipBytes bytes

 LDA skipBytes          ; Set skipBytes = 0 so we don't skip any bytes from the
 BEQ load3              ; remaining sectors (as we only want to skip bytes from
 LDA #0                 ; the first sector)
 STA skipBytes

.load3

 INC tslIndex           ; Set tslIndex = tslIndex + 2 to point to the next track
 INC tslIndex           ; and sector pair in the track/sector list

 LDY tslIndex           ; Set track to the track number from the next pair in
 LDA trackSector,Y      ; the track/sector list
 STA track

 LDA trackSector+1,Y    ; Set sector to the sector number from the next pair in
 STA sector             ; the track/sector list

 BNE load1              ; If either the track or sector number is non-zero, loop
 LDA track              ; back to load1 to load the next sector
 BNE load1

.load4

 RTS                    ; Return from the subroutine