; Program Name: PRG_6BP.S ; Version: 1.002 ; Assembly Instructions: ; Assemble in PC-relative mode and save with a TOS extension. ; Execution Instructions: ; Before this program is executed, trap 11 must be installed via the ; execution of program PRG_6AP.TOS. In addition, this program uses traps ; installed by CUSTOM.PRG. Execute from the desktop or via SPAWN.TTP. ; Program Function: ; Prints the content of register A7 during various stages of execution ; while the state of the processor is varied from user mode to supervisor ; mode, from supervisor mode back to user mode, from user mode to supervisor ; mode a second time and from supervisor mode back to user mode a second time. ; In this program, custom trap #11 is used to toggle the state of the ; processor. calculate_program_size: lea -$102(pc), a1 ; Fetch basepage start address. lea program_end, a0 ; Fetch program end address. trap #6 ; Return unused memory to op system. print_heading: lea heading, a0 bsr.s print_string ; NOTE: During this section of the program, no user stack has yet been ; assigned, therefore, the user stack address is that of the default ; user stack assigned by the system when execution commences. print_address_of_default_user_stack: lea header_1, a0 bsr.s print_string move.l a7, d1 ; Convert address to ASCII hexadecimal. trap #5 bsr.s print_string bsr.s print_newline invoke_custom_super_mode_trap: trap #11 ; Sets bit 13 of SR to 1 and prints SSP. print_current_SSP: ; SSP = address of supervisor stack. lea header_2, a0 ; Did invocation of trap #11 alter the address bsr.s print_string ; in the supervisor stack pointer? move.l a7, d1 ; Convert to ASCII hexadecimal. trap #5 bsr.s print_string bsr.s print_newline bsr.s print_newline enter_user_mode: andi.w #$DFFF, SR ; Sets bit 13 of status register to zero. ; NOTE: During this section of the program, a user stack is assigned. The ; user stack address is that of the label "stack". print_address_of_assigned_user_stack: lea header_3, a0 bsr.s print_string lea stack, a7 move.l a7, d1 ; Convert to ASCII hexadecimal. trap #5 bsr.s print_string bsr.s print_newline invoke_custom_super_mode_trap_again: trap #11 ; Sets bit 13 of SR to 1 and prints SSP. print_current_SSP_again: ; Did invocation of trap #11 alter the address lea header_4, a0 ; in the supervisor stack pointer? bsr.s print_string move.l a7, d1 ; Convert to ASCII hexadecimal. trap #5 bsr.s print_string bsr.s print_newline enter_user_mode_again: andi.w #$DFFF, SR ; Sets bit 13 of status register to zero. print_address_of_assigned_user_stack_again: lea header_5, a0 bsr.s print_string move.l a7, d1 ; Convert to ASCII hexadecimal. trap #5 bsr.s print_string bsr.s print_newline terminate: trap #8 ; ; 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 heading: dc.b 'PRG_6BP Execution Results => Content of A7:',$D,$A,$D,$A,0 header_1: dc.b ' NO USER STACK ASSIGNED',$D,$A dc.b ' Start of program: ',0 header_2: dc.b ' After trap 11 invocation: ',0 header_3: dc.b ' USER STACK ASSIGNED',$D,$A dc.b ' After force to user mode: ',0 header_4: dc.b ' After trap 11 invocation: ',0 header_5: dc.b ' After force to user mode: ',0 bss align ds.l 96 stack: ds.l 0 program_end: ds.l 0 end