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Elite on the BBC Micro

Utility routines: BRBR (6502SP version)

Name: BRBR [View in context] Type: Subroutine [Compare versions] Category: Utility routines Summary: The standard BRKV handler for the game
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 MRBRK 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 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