Keyboard: write_fe4e

       Name: write_fe4e                                              [Show more]
       Type: Subroutine
   Category: Keyboard
    Summary: Implement the write_fe4e command (update the System VIA interrupt
             enable register)
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * tube_table calls write_fe4e


 This routine is run when the parasite sends a write_fe4e command. It updates
 the System VIA interrupt enable register in the I/O processor to the value
 sent by the parasite, and returns that value back to the parasite once the
 register has been set, so the parasite can know when the register has been
 updated.


.write_fe4e

 JSR tube_get           \ Get the parameter from the parasite for the command:
                        \
                        \   =write_fe4e(value)
                        \
                        \ and store it as follows:
                        \
                        \   * A = new value for the interrupt register

 STA VIA+&4E            \ Set 6522 System VIA interrupt enable register IER
                        \ (SHEILA &4E) to the new value

 JMP tube_put           \ Send A back to the parasite and return from the
                        \ subroutine using a tail call