add interrupt init code (and increase rtc tick rate)

sw/kernel/interrupts/interrupt.s

@@ -0,0 +1,43 @@
+.MACPACK generic
+
+.autoimport
+
+.export   _irq_int, _nmi_int
+.export _register_irq
+
+IRQ_CMD_ADDR    = $effc
+IRQ_DAT_ADDR    = $effd
+
+IRQ_CMD_READIRQ = $00
+
+.proc _nmi_int
+rti
+.endproc
+
+
+; _irq_int
+.proc _irq_int
+    ; Load IRQ number
+    lda #IRQ_CMD_READIRQ
+    sta IRQ_CMD_ADDR
+    lda IRQ_DAT_ADDR
+    ; shift by 2 (oh so only 128 interrupts are supported lol)
+    lsr
+    tax
+    jmp (irq_table,x)
+    ; use that to index jump table
+.endproc
+
+; void register_irq(void* addr, uint8_t irqn);
+.proc _register_irq
+    tax
+    jsr popa
+    sta irq_table,x
+    jsr popa
+    sta irq_table+1,x
+    rts
+.endproc
+
+.data
+; interrupt handler jump table
+irq_table: .res 256