[arch][m68k] add exception and irq processing

-Add interrupt controller and timer support for qemu virt machine
-Switch tty read to irq driven as well

arch/m68k/arch.c

@@ -14,6 +14,10 @@
 
 void arch_early_init(void) {
     LTRACE;
+
+    // set the exception vector base
+    extern uint32_t exc_vectors[256];
+    asm("movec %0, %%vbr" :: "r"(exc_vectors));
 }
 
 void arch_init(void) {

arch/m68k/asm.S

@@ -26,3 +26,4 @@ FUNCTION(m68k_context_switch)
     // return to new PC
     rts
 END_FUNCTION(m68k_context_switch)
+

arch/m68k/exceptions.c

@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2021 Travis Geiselbrecht
+ *
+ * Use of this source code is governed by a MIT-style
+ * license that can be found in the LICENSE file or at
+ * https://opensource.org/licenses/MIT
+ */
+#include <arch/m68k.h>
+#include <inttypes.h>
+#include <lk/debug.h>
+#include <lk/trace.h>
+#include <kernel/thread.h>
+
+#define LOCAL_TRACE 0
+
+// defined in platform interrupt controller
+extern enum handler_return m68k_platform_irq(uint8_t irq);
+
+void m68k_exception(void *frame, uint8_t code) {
+    LTRACEF("frame %p, code %hhu\n", frame, code);
+
+    panic("unimplemented exception %hhu\n", code);
+}
+
+void m68k_irq(void *frame, uint8_t code) {
+    LTRACEF("frame %p, code %hhu\n", frame, code);
+
+    if (unlikely(code == 0)) {
+        // spurious interrupt
+        return;
+    }
+
+    enum handler_return ret = m68k_platform_irq(code);
+    if (ret == INT_RESCHEDULE) {
+        thread_preempt();
+    }
+}

arch/m68k/exceptions_asm.S

@@ -0,0 +1,83 @@
+/*
+ * Copyright (c) 2021 Travis Geiselbrecht
+ *
+ * Use of this source code is governed by a MIT-style
+ * license that can be found in the LICENSE file or at
+ * https://opensource.org/licenses/MIT
+ */
+#include <lk/asm.h>
+
+.text
+
+.macro irq_vector n
+m68k_irq_vector_\n:
+    moveml  %d0-%d7/%a0-%a6, %sp@-
+
+    pea     \n
+    movel   %sp,%sp@-
+    jsr     m68k_irq
+    addaw   #8, %sp
+
+    moveml  %sp@+, %d0-%d7/%a0-%a6
+    rte
+.endm
+
+irq_vector 0
+irq_vector 1
+irq_vector 2
+irq_vector 3
+irq_vector 4
+irq_vector 5
+irq_vector 6
+irq_vector 7
+
+.macro exception_vector name n
+\name:
+    moveml  %d0-%d7/%a0-%a6, %sp@-
+
+    pea     \n
+    movel   %sp,%sp@-
+    jsr     m68k_exception
+    addaw   #8, %sp
+
+    moveml  %sp@+, %d0-%d7/%a0-%a6
+    rte
+.endm
+
+exception_vector m68k_access_fault 2
+exception_vector m68k_address_error 3
+exception_vector m68k_illegal_vector 4
+exception_vector m68k_div_by_zero 5
+exception_vector m68k_chk 6
+exception_vector m68k_trap 7
+exception_vector m68k_priv_violation 8
+exception_vector m68k_trace 9
+exception_vector m68k_unimp_aline 10
+exception_vector m68k_unimp_fline 11
+
+.section .text.vectab
+.align 4
+DATA(exc_vectors)
+.org 0x8
+    .long m68k_access_fault
+    .long m68k_address_error
+    .long m68k_illegal_vector
+    .long m68k_div_by_zero
+    .long m68k_chk
+    .long m68k_trap
+    .long m68k_priv_violation
+    .long m68k_trace
+    .long m68k_unimp_aline
+    .long m68k_unimp_fline
+.org 0x60
+    .long m68k_irq_vector_0
+    .long m68k_irq_vector_1
+    .long m68k_irq_vector_2
+    .long m68k_irq_vector_3
+    .long m68k_irq_vector_4
+    .long m68k_irq_vector_5
+    .long m68k_irq_vector_6
+    .long m68k_irq_vector_7
+.org 4*256
+END_DATA(exc_vectors)
+

arch/m68k/include/arch/arch_thread.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015 Travis Geiselbrecht
+ * Copyright (c) 2021 Travis Geiselbrecht
  *
  * Use of this source code is governed by a MIT-style
  * license that can be found in the LICENSE file or at

arch/m68k/include/arch/microblaze.h

@@ -1,24 +0,0 @@
-/*
- * Copyright (c) 2015 Travis Geiselbrecht
- *
- * Use of this source code is governed by a MIT-style
- * license that can be found in the LICENSE file or at
- * https://opensource.org/licenses/MIT
- */
-#pragma once
-
-#if 0
-static inline uint32_t mb_read_msr(void) {
-    uint32_t temp;
-    __asm__ volatile(
-        "mfs    %0, rmsr;" : "=r" (temp));
-
-    return temp;
-}
-
-static inline void mb_write_msr(uint32_t val) {
-    __asm__ volatile(
-        "mts    rmsr, %0" :: "r" (val));
-}
-#endif
-

arch/m68k/rules.mk

@@ -5,11 +5,12 @@ MODULE := $(LOCAL_DIR)
 MODULE_SRCS += \
 	$(LOCAL_DIR)/arch.c \
 	$(LOCAL_DIR)/asm.S \
+	$(LOCAL_DIR)/exceptions.c \
+	$(LOCAL_DIR)/exceptions_asm.S \
 	$(LOCAL_DIR)/start.S \
 	$(LOCAL_DIR)/thread.c \
 
 #	$(LOCAL_DIR)/asm.S \
-	$(LOCAL_DIR)/exceptions.c \
 	$(LOCAL_DIR)/cache.c \
 	$(LOCAL_DIR)/cache-ops.S \
 	$(LOCAL_DIR)/ops.S \