diff options
| -rw-r--r-- | interrupts.asm | 42 |
1 files changed, 26 insertions, 16 deletions
diff --git a/interrupts.asm b/interrupts.asm index 78ff87d..0a3fcfa 100644 --- a/interrupts.asm +++ b/interrupts.asm @@ -1,21 +1,7 @@ ;;; interrupt handling code ;; Current interrupt mode. IM 1 and friends will modify - ;; this. - - ;; 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 int_opcode and set epc (or int_jump) to point - ;; there. - - ;; IM 1: RST 38 is executed on every 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. + ;; this, it can be any of 0, 1, 2. int_mode: dc.b 0 ;; 0 if interrupts are turned on. @@ -42,6 +28,15 @@ int_jump: dc.l 0 ;; 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. int_opcode: dc.b 0 dc.b $c3 ; JP immed.w int_return: dc.w 0 ; the destination address @@ -57,7 +52,7 @@ HOLD_INTS MACRO moveq.b #1,int_held ; 4 cycles ENDM - ;; This is a macro to release a held interrupts. + ;; This is a macro to release a held interrupt. CONTINUE_INTS MACRO bsr ints_continue ; 18 cycles ENDM @@ -78,15 +73,30 @@ ints_continue_pending: move.b int_mode, + ;; 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 int_opcode and set epc (or int_jump) to point + ;; there. int_do_mode0: rts ;; This routine emulates a mode 1 interrupt. + + ;; IM 1: RST 38 is executed on every interrupt. int_do_mode1: rts ;; 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. int_do_mode2: rts |