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Elite on the BBC Micro

Keyboard: DKS3 [Master version]

Name: DKS3 [Show more] Type: Subroutine Category: Keyboard Summary: Toggle a configuration setting and emit a beep
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: * DK4 calls DKS3

This is called when the game is paused and a key is pressed that changes the game's configuration. Specifically, this routine toggles the configuration settings for the following keys: * CAPS LOCK toggles keyboard flight damping (0) * A toggles keyboard auto-recentre (1) * X toggles author names on start-up screen (2) * F toggles flashing console bars (3) * Y toggles reverse joystick Y channel (4) * J toggles reverse both joystick channels (5) * K toggles keyboard and joystick (6) The numbers in brackets are the configuration options that we pass in Y. We pass the ASCII code of the key that has been pressed in X, and the option to check it against in Y, so this routine is typically called in a loop that loops through the various configuration option. Arguments: X The ASCII code of the key that's been pressed Y The number of the configuration option to check against from the list above (i.e. Y must be from 0 to 6)
.DKS3 TXA \ Copy the ASCII code of the key that has been pressed \ into A CMP CKEYS,Y \ If the pressed key doesn't match the configuration key BNE Dk3 \ for option Y (as listed in the CKEYS table), then jump \ to Dk3 to return from the subroutine LDA DAMP,Y \ The configuration keys listed in CKEYS correspond to EOR #&FF \ the configuration option settings from DAMP onwards, STA DAMP,Y \ so to toggle a setting, we fetch the existing byte \ from DAMP+Y, invert it and put it back (0 means no \ and &FF means yes in the configuration bytes, so \ this toggles the setting) BPL P%+5 \ If the result has a clear bit 7 (i.e. we just turned \ the option off), skip the following instruction JSR BELL \ We just turned the option on, so make a standard \ system beep, so in all we make two beeps JSR BELL \ Make a beep sound so we know something has happened TYA \ Store Y and A on the stack so we can retrieve them PHA \ below LDY #20 \ Wait for 20 vertical syncs (20/50 = 0.4 seconds) JSR DELAY PLA \ Restore A and Y from the stack TAY .Dk3 RTS \ Return from the subroutine