; Program Name: PRG_6AP.S ; Version: 1.002 ; Assembly Instructions: ; Assemble in PC-relative mode and save with a TOS extension. ; Program Function: ; This is a LSR program that installs custom trap #11, which is invoked ; by PRG_6BP.TOS. This program uses traps installed by CUSTOM.PRG. program_start: ; Calculate program size and retain result. lea program_end, a3 ; Fetch program end address. suba.l 4(a7), a3 ; Subtract basepage address. enter_supervisor_mode: trap #0 ; Sets bit 13 of status register to 1. install_trap_11_routine: ; Note: pointer = vector = pointer. lea trap_11_routine, a0 ; Fetch address of trap #11 routine. move.l a0, $AC ; Store trap address at pointer address. enter_user_mode: andi.w #$DFFF, SR ; Sets bit 13 of status register to 0. relinquish_processor_control: ; Maintain memory residency. move.w #0, -(sp) ; Exit code. move.l a3, -(sp) ; Program size. move.w #$31, -(sp) ; Function = ptermres = GEMDOS $31. trap #1 trap_11_routine: ; When trap #11 is invoked, the CPU pushes the calling program's return ; address onto the supervisor stack, then it pushes the calling program's ; status register contents onto the supervisor stack. ; This custom trap #11 handler sets bit #13 of the calling program's status ; register. The bset instruction can be used to set a bit in the first ; byte of the word on the top of the stack. Bit #13 of the status register ; is bit #5 of that byte. Note: to set a bit means to make it equal to 1. ; When the rte instruction is executed, the CPU will return to the calling ; program with the altered copy of its status register, and the calling ; program will now be executing in supervisor mode. ; Register A7 will contain the address of the supervisor stack. The calling ; program now has complete control of the system. But a decision about ; which stack is to be used must be made. ; The calling program can choose to continue with A7 pointing to the ; supervisor stack, or it can save the contents of A7 = SSP and load the ; address of a user stack into A7. Processing can continue in that manner ; until it is necessary to return to user mode. The return to user mode ; can be accomplished by reloading A7 with the SSP, then by resetting bit ; #13 of the status register. Note: resetting a bit means to make it equal ; to 0. print_current_SSP: ; SSP = address of supervisor stack. lea header_1, a0 bsr.s print_string move.l a7, d1 ; Convert to ASCII hexadecimal. trap #5 bsr.s print_string bsr.s print_newline bset #5, (sp) ; The invoking program will be executing in rte ; supervisor mode upon return. ; ; SUBROUTINES ; print_string: pea (a0) move.w #9, -(sp) trap #1 addq.l #6, sp rts print_newline: lea newline, a0 bsr.s print_string rts data newline: dc.b $D,$A,0 header_1: dc.b ' During trap 11 invocation: ',0 bss align program_end: ds.l 0 end