Utility routines: BRBR

       Name: BRBR                                                    [Show more]
       Type: Subroutine
   Category: Utility routines
    Summary: The standard BRKV handler for the game
    Context: See this subroutine in context in the source code
 Variations: See code variations for this subroutine in the different versions
 References: This subroutine is called as follows:
             * BRKBK calls BRBR


 This routine is used to display error messages, before restarting the game.
 When called, it makes a beep and prints the system error message in the block
 pointed to by (&FD &FE), which is where the MOS will put any system errors. It
 then waits for a key press and restarts the game.

 BRKV is set to this routine in the decryption routine at DEEOR just before the
 game is run for the first time, and at the end of the SVE routine after the
 disc access menu has been processed. In other words, this is the standard
 BRKV handler for the game, and it's swapped out to MEBRK for disc access
 operations only.

 When it is the BRKV handler, the routine can be triggered using a BRK
 instruction. The main differences between this routine and the MEBRK handler
 that is used during disc access operations are that this routine restarts the
 game rather than returning to the disc access menu, and this handler
 decrements the brkd counter.


.BRBR

 DEC brkd               \ Decrement the brkd counter

 LDX #&FF               \ Set the stack pointer to &01FF, which is the standard
 TXS                    \ location for the 6502 stack, so this instruction
                        \ effectively resets the stack

 JSR backtonormal       \ Disable the keyboard and set the SVN flag to 0

 TAY                    \ The call to backtonormal sets A to 0, so this sets Y
                        \ to 0, which we use as a loop counter below

 LDA #7                 \ Set A = 7 to generate a beep before we print the error
                        \ message

.BRBRLOOP

 JSR OSWRCH             \ Print the character in A, which contains a line feed
                        \ on the first loop iteration, and then any non-zero
                        \ characters we fetch from the error message

 INY                    \ Increment the loop counter

 LDA (&FD),Y            \ Fetch the Y-th byte of the block pointed to by
                        \ (&FD &FE), so that's the Y-th character of the message
                        \ pointed to by the MOS error message pointer

 BNE BRBRLOOP           \ If the fetched character is non-zero, loop back to the
                        \ JSR OSWRCH above to print the it, and keep looping
                        \ until we fetch a zero (which marks the end of the
                        \ message)

 JMP BR1                \ Jump to BR1 to restart the game