The KEY1 subroutine - Elite on the BBC Micro and NES

       Name: KEY1                                                    [Show more]
       Type: Subroutine
   Category: Keyboard
    Summary: The main keyboard interrupt handler (KEYV points here)
    Context: See this subroutine in context in the source code
 References: No direct references to this subroutine in this source file


.KEY1

 PHP                    \ Store the flags on the stack

 BIT KEYB               \ If bit 7 of KEYB is set then we are currently reading
 BMI P%+4               \ from the keyboard with an OS command, so skip the
                        \ following two instructions

 PLP                    \ We aren't currently reading from the keyboard with an
 RTS                    \ OS command, so retrieve the flags from the stack and
                        \ return from the subroutine

 PLP                    \ If we get here then we are currently reading from the
                        \ keyboard with an OS command, so retrieve the flags on
                        \ the stack before passing the interrupt through for the
                        \ OS to process the key press

 JMP (S%+4)             \ Jump to the original value of KEYV, which is stored in
                        \ S%+4, so the OS can process the key press as normal,
                        \ and return from the subroutine using a tail call

[X]

Variable KEYB in workspace S% (Part 1 of 2)

This flag indicates whether we are currently reading from the keyboard using OSRDCH or OSWORD, so the keyboard interrupt handler at KEY1 knows whether to pass key presses on to the OS

[X]

Workspace S% (Part 1 of 2) (category: Workspaces)

Vector addresses, compass shape and configuration settings

Keyboard: KEY1

[Acorn Electron version]