Save and load: rdrght

       Name: rdrght                                                  [Show more]
       Type: Subroutine
   Category: Save and load
    Summary: Check that this is the correct track
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * trytrk calls rdrght


 This routine is almost identical to the RDRIGHT routine in Apple DOS 3.3.
 It omits the code that saves the destination track, as this is not required.

 For a detailed look at how DOS works, see the book "Beneath Apple DOS" by Don
 Worth and Pieter Lechner. In particular, see chapter 4 for the layout of the
 VTOC, catalog sector, file entry and file/track list.

 Elite uses different label names to the original DOS 3.3 source, but the code
 is the same.

 This code forms part of the RWTS ("read/write track sector") layer from Apple
 DOS, which was written by Randy Wigginton and Steve Wozniak. It implements the
 low-level functions to read and write Apple disks, and is included in Elite so
 the game can use the memory that's normally allocated to DOS for its own use.


.rdrght

 LDY idfld+2            ; RDRIGHT  LDY TRACK      ; ON THE RIGHT TRACK?
 CPY track              ;          CPY CURTRK
 BEQ rttrk              ;          BEQ RTTRK      ; IF SO, GOOD
                        ; * NO, DRIVE WAS ON A DIFFERENT TRACK. TRY
                        ; * RESEEKING/RECALIBRATING FROM THIS TRACK
                        ;          LDA CURTRK     ; PRESERVE DESTINATION TRACK
                        ;          PHA
                        ;          TYA
                        ;          JSR SETTRK
                        ;          PLA
 DEC seeks              ;          DEC SEEKCNT    ; SHOULD WE RESEEK?
 BNE trytr6             ;          BNE RESEEK     ; =>YES, RESEEK
 BEQ trytr5             ;          BEQ RECAL      ; =>NO, RECALIBRATE!