diff options
Diffstat (limited to 'interrupts.s.m4')
| -rw-r--r-- | interrupts.s.m4 | 116 |
1 files changed, 58 insertions, 58 deletions
diff --git a/interrupts.s.m4 b/interrupts.s.m4 index 66b71d8..8982cb3 100644 --- a/interrupts.s.m4 +++ b/interrupts.s.m4 @@ -1,43 +1,43 @@ -;;; interrupt handling code, in -*- asm -*- +||| interrupt handling code, in -*- gas -*- .data - ;; Current interrupt mode. IM 1 and friends will modify - ;; this. It can be any of 0, 1, 2. + || Current interrupt mode. IM 1 and friends will modify + || this. It can be any of 0, 1, 2. int_mode: dc.b 0 - ;; 0 if the emulated device doesn't want interrupts. - ;; 1 if interrupts are turned on. + || 0 if the emulated device doesn't want interrupts. + || 1 if interrupts are turned on. int_enabled: dc.b 1 - ;; In interrupt mode 0, an interrupt will force a byte onto - ;; the data bus for the processor to execute. To handle - ;; those, the emulator will store the bus byte in int_opcode, - ;; which is followed by an absolute jump to the "next - ;; instruction". The value of int_jump will then be - ;; &int_opcode. - ;; - ;; This differs slightly from what I understand to be actual - ;; handling. The hardware will fetch an immediate argument to - ;; the interrupting instruction from the next location in - ;; memory. - ;; - ;; This emulator, on the other hand, will fetch the immediate - ;; argument from the JP instruction in the shim, and then - ;; dance off into la-la land. + || In interrupt mode 0, an interrupt will force a byte onto + || the data bus for the processor to execute. To handle + || those, the emulator will store the bus byte in int_opcode, + || which is followed by an absolute jump to the "next + || instruction". The value of int_jump will then be + || &int_opcode. + || + || This differs slightly from what I understand to be actual + || handling. The hardware will fetch an immediate argument to + || the interrupting instruction from the next location in + || memory. + || + || This emulator, on the other hand, will fetch the immediate + || argument from the JP instruction in the shim, and then + || dance off into la-la land. int0_opcode: dc.b 0 - dc.b $c3 ; JP immed.w -int0_return: dc.w 0 ; the destination address + dc.b $c3 | JP immed.w +int0_return: dc.w 0 | the destination address .text - ;; This is the interrupt routine. It can come at any point - ;; during an instruction, though routines that use a5 (e.g. by - ;; calling C subroutines) will have to turn off or hold - ;; interrupts. - ;; - ;; Routines that call into TIOS will have to remove this - ;; interrupt handler. + || This is the interrupt routine. It can come at any point + || during an instruction, though routines that use a5 (e.g. by + || calling C subroutines) will have to turn off or hold + || interrupts. + || + || Routines that call into TIOS will have to remove this + || interrupt handler. int_handler: sub.l #INT_OFFSET,a5 rte @@ -46,18 +46,18 @@ int_handler: int_nevermind: rts do_interrupt: - add.l #INT_OFFSET,a5 ; clear the interrupt flag - pea 0(a5,d0.w) ; allows us to rts properly + add.l #INT_OFFSET,a5 | clear the interrupt flag + pea 0(a5,d0.w) | allows us to rts properly - tst.b int_enabled ; 4 cycles - beq.b int_nevermind ; 8 cycles not taken - ;; Common case: interrupts enabled, fall through + tst.b int_enabled | 4 cycles + beq.b int_nevermind | 8 cycles not taken + || Common case: interrupts enabled, fall through - ;; Since this is an instruction all its own, we have D0, D1, - ;; and D2 available. + || Since this is an instruction all its own, we have D0, D1, + || and D2 available. - ;; Interrupts are most often in mode 1, then mode 2, and - ;; almost never in mode 0. + || Interrupts are most often in mode 1, then mode 2, and + || almost never in mode 0. move.b int_mode,d0 cmpi.b #1,d0 beq int_do_mode2 @@ -67,49 +67,49 @@ do_interrupt: beq int_do_mode0 rts - ;; This routine emulates a mode 0 interrupt. + || This routine emulates a mode 0 interrupt. - ;; IM 0: A byte is placed on the bus and executed as if it - ;; were inline in the program. This emulator will put that - ;; byte into int0_opcode and set epc (or int_jump) to point - ;; there. + || IM 0: A byte is placed on the bus and executed as if it + || were inline in the program. This emulator will put that + || byte into int0_opcode and set epc (or int_jump) to point + || there. int_do_mode0: move epc,int0_opcode rts - ;; This routine emulates a mode 1 interrupt. + || This routine emulates a mode 1 interrupt. - ;; IM 1: RST 38 is executed on every interrupt. This is what - ;; the TI-83+ uses almost all the time. + || IM 1: RST 38 is executed on every interrupt. This is what + || the TI-83+ uses almost all the time. int_do_mode1: jmp emu_op_ff - ;; This routine emulates a mode 2 interrupt. + || This routine emulates a mode 2 interrupt. - ;; IM 2: Vectored, the address jumped to is as follows: - ;; - ;; (I << 8) | (byte & 0xfe) - ;; - ;; where I is the I register, and byte is the byte that was - ;; found on the bus. + || IM 2: Vectored, the address jumped to is as follows: + || + || (I << 8) | (byte & 0xfe) + || + || where I is the I register, and byte is the byte that was + || found on the bus. int_do_mode2: rts - ;; This routine emulates a non-maskable interrupt. + || This routine emulates a non-maskable interrupt. int_do_nmi: rts - ;; This routine is used by the emulated DI instruction, which - ;; turns off emulator interrupts. + || This routine is used by the emulated DI instruction, which + || turns off emulator interrupts. ints_stop: rts - ;; This routine is used by the emulated EI instruction, which - ;; turns on emulator interrupts. + || This routine is used by the emulated EI instruction, which + || turns on emulator interrupts. ints_start: rts |