Move variables from assembler to C code.

Define macro VAR16FIXED for declaring a variable at a fixed location.
Introduce new file src/misc.c, and move non int15 calls from system.c
    to it.
Implement all fixed location variables in C code.
Move IDT/GDT defs to misc.c.  Remove unused gdt entry 1.

15 files changed, 248 insertions, 253 deletions

diff --git a/src/biosvar.h b/src/biosvar.h
index 51056964..5dc113f2 100644
--- a/src/biosvar.h
+++ b/src/biosvar.h
@@ -15,18 +15,18 @@
  * Interupt vector table
  ****************************************************************/
 
-struct ivec {
+struct rmode_IVT {
     union {
         struct {
             u16 offset;
             u16 seg;
         };
         u32 segoff;
-    };
+    } ivec[256];
 };
 
 #define SET_IVT(vector, seg, off)                                       \
-    SET_FARVAR(SEG_IVT, ((struct ivec *)0)[vector].segoff, ((seg) << 16) | (off))
+    SET_FARVAR(SEG_IVT, ((struct rmode_IVT *)0)->ivec[vector].segoff, ((seg) << 16) | (off))
 
 
 /****************************************************************
@@ -284,6 +284,6 @@ struct bios_config_table_s {
     u8 feature1, feature2, feature3, feature4, feature5;
 } PACKED;
 
-extern struct bios_config_table_s BIOS_CONFIG_TABLE;
+extern struct bios_config_table_s BIOS_CONFIG_TABLE __aligned(1);
 
 #endif // __BIOSVAR_H
diff --git a/src/cbt.c b/src/cbt.c
deleted file mode 100644
index bb7aea3d..00000000
--- a/src/cbt.c
+++ /dev/null
@@ -1,42 +0,0 @@
-// BIOS configuration table.
-//
-// Copyright (C) 2008  Kevin O'Connor <kevin@koconnor.net>
-// Copyright (C) 2002  MandrakeSoft S.A.
-//
-// This file may be distributed under the terms of the GNU LGPLv3 license.
-
-#include "biosvar.h" // CONFIG_BIOS_TABLE
-
-// DMA channel 3 used by hard disk BIOS
-#define CBT_F1_DMA3USED (1<<7)
-// 2nd interrupt controller (8259) installed
-#define CBT_F1_2NDPIC   (1<<6)
-// Real-Time Clock installed
-#define CBT_F1_RTC      (1<<5)
-// INT 15/AH=4Fh called upon INT 09h
-#define CBT_F1_INT154F  (1<<4)
-// wait for external event (INT 15/AH=41h) supported
-#define CBT_F1_WAITEXT  (1<<3)
-// extended BIOS area allocated (usually at top of RAM)
-#define CBT_F1_EBDA     (1<<2)
-// bus is Micro Channel instead of ISA
-#define CBT_F1_MCA      (1<<1)
-// system has dual bus (Micro Channel + ISA)
-#define CBT_F1_MCAISA   (1<<0)
-
-// INT 16/AH=09h (keyboard functionality) supported
-#define CBT_F2_INT1609  (1<<6)
-
-struct bios_config_table_s BIOS_CONFIG_TABLE __aligned(1) VAR16 = {
-    .size     = sizeof(BIOS_CONFIG_TABLE) - 2,
-    .model    = CONFIG_MODEL_ID,
-    .submodel = CONFIG_SUBMODEL_ID,
-    .biosrev  = CONFIG_BIOS_REVISION,
-    .feature1 = (
-        CBT_F1_2NDPIC | CBT_F1_RTC | CBT_F1_EBDA
-        | (CONFIG_KBD_CALL_INT15_4F ? CBT_F1_INT154F : 0)),
-    .feature2 = CBT_F2_INT1609,
-    .feature3 = 0,
-    .feature4 = 0,
-    .feature5 = 0,
-};
diff --git a/src/config.h b/src/config.h
index 8c4b2f02..d573726e 100644
--- a/src/config.h
+++ b/src/config.h
@@ -111,12 +111,12 @@
 #define SEG_BIOS     0xf000
 
 // Segment definitions in protected mode (see rombios32_gdt in romlayout.S)
-#define SEG32_MODE32_CS    (2 << 3)
-#define SEG32_MODE32_DS    (3 << 3)
-#define SEG32_MODE16_CS    (4 << 3)
-#define SEG32_MODE16_DS    (5 << 3)
-#define SEG32_MODE16BIG_CS (6 << 3)
-#define SEG32_MODE16BIG_DS (7 << 3)
+#define SEG32_MODE32_CS    (1 << 3)
+#define SEG32_MODE32_DS    (2 << 3)
+#define SEG32_MODE16_CS    (3 << 3)
+#define SEG32_MODE16_DS    (4 << 3)
+#define SEG32_MODE16BIG_CS (5 << 3)
+#define SEG32_MODE16BIG_DS (6 << 3)
 
 // Debugging levels.  If non-zero and CONFIG_DEBUG_LEVEL is greater
 // than the specified value, then the corresponding irq handler will
diff --git a/src/disk.c b/src/disk.c
index d5c7df27..13cb1f3f 100644
--- a/src/disk.c
+++ b/src/disk.c
@@ -712,3 +712,6 @@ handle_76()
     SET_BDA(disk_interrupt_flag, 0xff);
     eoi_pic2();
 }
+
+// Old Fixed Disk Parameter Table (newer tables are in the ebda).
+struct fdpt_s OldFDPT VAR16FIXED(0xe401);
diff --git a/src/floppy.c b/src/floppy.c
index 6214acba..43e6c1eb 100644
--- a/src/floppy.c
+++ b/src/floppy.c
@@ -39,6 +39,23 @@ struct floppy_ext_dbt_s diskette_param_table2 VAR16_32 = {
     .drive_type     = 4,    // drive type in cmos
 };
 
+// Since no provisions are made for multiple drive types, most
+// values in this table are ignored.  I set parameters for 1.44M
+// floppy here
+struct floppy_dbt_s diskette_param_table VAR16FIXED(0xefc7) = {
+    .specify1       = 0xAF,
+    .specify2       = 0x02, // head load time 0000001, DMA used
+    .shutoff_ticks  = 0x25,
+    .bps_code       = 0x02,
+    .sectors        = 18,
+    .interblock_len = 0x1B,
+    .data_len       = 0xFF,
+    .gap_len        = 0x6C,
+    .fill_byte      = 0xF6,
+    .settle_time    = 0x0F,
+    .startup_time   = 0x08,
+};
+
 void
 floppy_drive_setup()
 {
diff --git a/src/floppy_dbt.c b/src/floppy_dbt.c
deleted file mode 100644
index a9882015..00000000
--- a/src/floppy_dbt.c
+++ /dev/null
@@ -1,24 +0,0 @@
-// Floppy controller parameter table.
-//
-// Copyright (C) 2002  MandrakeSoft S.A.
-//
-// This file may be distributed under the terms of the GNU LGPLv3 license.
-
-#include "disk.h" // struct floppy_dbt_s
-
-// Since no provisions are made for multiple drive types, most
-// values in this table are ignored.  I set parameters for 1.44M
-// floppy here
-struct floppy_dbt_s diskette_param_table __aligned(1) VAR16 = {
-    .specify1       = 0xAF,
-    .specify2       = 0x02, // head load time 0000001, DMA used
-    .shutoff_ticks  = 0x25,
-    .bps_code       = 0x02,
-    .sectors        = 18,
-    .interblock_len = 0x1B,
-    .data_len       = 0xFF,
-    .gap_len        = 0x6C,
-    .fill_byte      = 0xF6,
-    .settle_time    = 0x0F,
-    .startup_time   = 0x08,
-};
diff --git a/src/font.c b/src/font.c
index 99c7f435..3f8662f9 100644
--- a/src/font.c
+++ b/src/font.c
@@ -7,7 +7,7 @@
  * found at ftp://ftp.simtel.net/pub/simtelnet/msdos/screen/fntcol16.zip
  * This font is public domain
  */
-const u8 vgafont8[128*8] __aligned(1) VAR16 = {
+u8 vgafont8[128*8] VAR16FIXED(0xfa6e) = {
     0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
     0x7e, 0x81, 0xa5, 0x81, 0xbd, 0x99, 0x81, 0x7e,
     0x7e, 0xff, 0xdb, 0xff, 0xc3, 0xe7, 0xff, 0x7e,
diff --git a/src/misc.c b/src/misc.c
new file mode 100644
index 00000000..0c5f608d
--- /dev/null
+++ b/src/misc.c
@@ -0,0 +1,193 @@
+// Code for misc 16bit handlers and variables.
+//
+// Copyright (C) 2008  Kevin O'Connor <kevin@koconnor.net>
+// Copyright (C) 2002  MandrakeSoft S.A.
+//
+// This file may be distributed under the terms of the GNU LGPLv3 license.
+
+#include "bregs.h" // struct bregs
+#include "biosvar.h" // GET_BDA
+#include "util.h" // debug_enter
+#include "pic.h" // enable_hwirq
+
+// Amount of continuous ram under 4Gig
+u32 RamSize VAR16_32;
+// Amount of continuous ram >4Gig
+u64 RamSizeOver4G;
+
+
+/****************************************************************
+ * Misc 16bit ISRs
+ ****************************************************************/
+
+// INT 12h Memory Size Service Entry Point
+void VISIBLE16
+handle_12(struct bregs *regs)
+{
+    debug_enter(regs, DEBUG_HDL_12);
+    regs->ax = GET_BDA(mem_size_kb);
+}
+
+// INT 11h Equipment List Service Entry Point
+void VISIBLE16
+handle_11(struct bregs *regs)
+{
+    debug_enter(regs, DEBUG_HDL_11);
+    regs->ax = GET_BDA(equipment_list_flags);
+}
+
+// INT 05h Print Screen Service Entry Point
+void VISIBLE16
+handle_05(struct bregs *regs)
+{
+    debug_enter(regs, DEBUG_HDL_05);
+}
+
+// INT 10h Video Support Service Entry Point
+void VISIBLE16
+handle_10(struct bregs *regs)
+{
+    debug_enter(regs, DEBUG_HDL_10);
+    // dont do anything, since the VGA BIOS handles int10h requests
+}
+
+void VISIBLE16
+handle_nmi()
+{
+    debug_isr(DEBUG_ISR_nmi);
+    BX_PANIC("NMI Handler called\n");
+}
+
+void
+mathcp_setup()
+{
+    dprintf(3, "math cp init\n");
+    // 80x87 coprocessor installed
+    SETBITS_BDA(equipment_list_flags, 0x02);
+    enable_hwirq(13, entry_75);
+}
+
+// INT 75 - IRQ13 - MATH COPROCESSOR EXCEPTION
+void VISIBLE16
+handle_75()
+{
+    debug_isr(DEBUG_ISR_75);
+
+    // clear irq13
+    outb(0, PORT_MATH_CLEAR);
+    // clear interrupt
+    eoi_pic2();
+    // legacy nmi call
+    u32 eax=0, flags;
+    call16_simpint(0x02, &eax, &flags);
+}
+
+
+/****************************************************************
+ * BIOS_CONFIG_TABLE
+ ****************************************************************/
+
+// DMA channel 3 used by hard disk BIOS
+#define CBT_F1_DMA3USED (1<<7)
+// 2nd interrupt controller (8259) installed
+#define CBT_F1_2NDPIC   (1<<6)
+// Real-Time Clock installed
+#define CBT_F1_RTC      (1<<5)
+// INT 15/AH=4Fh called upon INT 09h
+#define CBT_F1_INT154F  (1<<4)
+// wait for external event (INT 15/AH=41h) supported
+#define CBT_F1_WAITEXT  (1<<3)
+// extended BIOS area allocated (usually at top of RAM)
+#define CBT_F1_EBDA     (1<<2)
+// bus is Micro Channel instead of ISA
+#define CBT_F1_MCA      (1<<1)
+// system has dual bus (Micro Channel + ISA)
+#define CBT_F1_MCAISA   (1<<0)
+
+// INT 16/AH=09h (keyboard functionality) supported
+#define CBT_F2_INT1609  (1<<6)
+
+struct bios_config_table_s BIOS_CONFIG_TABLE VAR16FIXED(0xe6f5) = {
+    .size     = sizeof(BIOS_CONFIG_TABLE) - 2,
+    .model    = CONFIG_MODEL_ID,
+    .submodel = CONFIG_SUBMODEL_ID,
+    .biosrev  = CONFIG_BIOS_REVISION,
+    .feature1 = (
+        CBT_F1_2NDPIC | CBT_F1_RTC | CBT_F1_EBDA
+        | (CONFIG_KBD_CALL_INT15_4F ? CBT_F1_INT154F : 0)),
+    .feature2 = CBT_F2_INT1609,
+    .feature3 = 0,
+    .feature4 = 0,
+    .feature5 = 0,
+};
+
+
+/****************************************************************
+ * GDT and IDT tables
+ ****************************************************************/
+
+struct descloc_s {
+    u16 length;
+    u32 addr;
+} PACKED;
+
+// Real mode IDT descriptor
+struct descloc_s rmode_IDT_info VAR16_32 = {
+    .length = sizeof(struct rmode_IVT) - 1,
+    .addr = (u32)MAKE_FARPTR(SEG_IVT, 0),
+};
+
+// Dummy IDT that forces a machine shutdown if an irq happens in
+// protected mode.
+u8 dummy_IDT VAR16_32;
+
+// Protected mode IDT descriptor
+struct descloc_s pmode_IDT_info VAR16_32 = {
+    .length = sizeof(dummy_IDT) - 1,
+    .addr = (u32)MAKE_FARPTR(SEG_BIOS, &dummy_IDT),
+};
+
+// GDT
+u64 rombios32_gdt[] VAR16_32 __aligned(8) = {
+    // First entry can't be used.
+    0x0000000000000000LL,
+    // 32 bit flat code segment (SEG32_MODE32_CS)
+    0x00cf9b000000ffffLL,
+    // 32 bit flat data segment (SEG32_MODE32_DS)
+    0x00cf93000000ffffLL,
+    // 16 bit code segment base=0xf0000 limit=0xffff (SEG32_MODE16_CS)
+    0x00009b0f0000ffffLL,
+    // 16 bit data segment base=0x0 limit=0xffff (SEG32_MODE16_DS)
+    0x000093000000ffffLL,
+    // 16 bit code segment base=0 limit=0xffffffff (SEG32_MODE16BIG_CS)
+    0x008f9b000000ffffLL,
+    // 16 bit data segment base=0 limit=0xffffffff (SEG32_MODE16BIG_DS)
+    0x008f93000000ffffLL,
+};
+
+// GDT descriptor
+struct descloc_s rombios32_gdt_48 VAR16_32 = {
+    .length = sizeof(rombios32_gdt) - 1,
+    .addr = (u32)MAKE_FARPTR(SEG_BIOS, rombios32_gdt),
+};
+
+
+/****************************************************************
+ * Misc fixed vars
+ ****************************************************************/
+
+char BiosCopyright[] VAR16FIXED(0xff00) =
+    "(c) 2002 MandrakeSoft S.A. Written by Kevin Lawton & the Bochs team.";
+
+// BIOS build date
+char BiosDate[] VAR16FIXED(0xfff5) = "06/23/99";
+
+u8 BiosModelId VAR16FIXED(0xfffe) = CONFIG_MODEL_ID;
+
+u8 BiosChecksum VAR16FIXED(0xffff);
+
+// XXX - Initial Interrupt Vector Offsets Loaded by POST
+u8 InitVectors[13] VAR16FIXED(0xfef3);
+
+// XXX - INT 1D - SYSTEM DATA - VIDEO PARAMETER TABLES
+u8 VideoParams[88] VAR16FIXED(0xf0a4);
diff --git a/src/null.c b/src/null.c
deleted file mode 100644
index be072ceb..00000000
--- a/src/null.c
+++ /dev/null
@@ -1,2 +0,0 @@
-// GCC does something odd when one uses -combine with just one .c
-// file.  So this dummy file makes gcc happy.
diff --git a/src/post.c b/src/post.c
index bfa65621..7093901c 100644
--- a/src/post.c
+++ b/src/post.c
@@ -245,8 +245,7 @@ _start()
     interactive_bootmenu();
 
     // Setup bios checksum.
-    extern char bios_checksum;
-    bios_checksum = -checksum((u8*)BUILD_BIOS_ADDR, BUILD_BIOS_SIZE - 1);
+    BiosChecksum = -checksum((u8*)BUILD_BIOS_ADDR, BUILD_BIOS_SIZE - 1);
 
     // Prep for boot process.
     make_bios_readonly();
diff --git a/src/romlayout.S b/src/romlayout.S
index c8b77935..b0dc6fd9 100644
--- a/src/romlayout.S
+++ b/src/romlayout.S
@@ -451,88 +451,21 @@ permanent_halt:
         ORG 0xe2c3
         IRQ_ENTRY nmi
 
-/****************************************************************
- * GDT and IDT tables (between 0xe2c3 - 0xe3fe)
- ****************************************************************/
-
-// Protected mode IDT descriptor
-//
-// I just make the limit 0, so the machine will shutdown
-// if an exception occurs during protected mode memory
-// transfers.
-//
-// Set base to f0000 to correspond to beginning of BIOS,
-// in case I actually define an IDT later
-// Set limit to 0
-        .type pmode_IDT_info, @object
-pmode_IDT_info:
-        .word 0x0000  // limit 15:00
-        .long 0xf0000 // base 16:47
-
-// Real mode IDT descriptor
-//
-// Set to typical real-mode values.
-// base  = 000000
-// limit =   03ff
-        .type rmode_IDT_info, @object
-rmode_IDT_info:
-        .word 0x03ff  // limit 15:00
-        .long 0       // base 16:47
-
-        .type rombios32_gdt_48, @object
-rombios32_gdt_48:
-        .word (rombios32_gdt_end - rombios32_gdt)
-        .long (BUILD_BIOS_ADDR + rombios32_gdt)
-
-        //.balign 8
-        .type rombios32_gdt, @object
-rombios32_gdt:
-        .word 0, 0, 0, 0
-        .word 0, 0, 0, 0
-        // 32 bit flat code segment (SEG32_MODE32_CS)
-        .word 0xffff, 0, 0x9b00, 0x00cf
-        // 32 bit flat data segment (SEG32_MODE32_DS)
-        .word 0xffff, 0, 0x9300, 0x00cf
-        // 16 bit code segment base=0xf0000 limit=0xffff (SEG32_MODE16_CS)
-        .word 0xffff, 0, 0x9b0f, 0x0000
-        // 16 bit data segment base=0x0 limit=0xffff (SEG32_MODE16_DS)
-        .word 0xffff, 0, 0x9300, 0x0000
-        // 16 bit code segment base=0 limit=0xffffffff (SEG32_MODE16BIG_CS)
-        .word 0xffff, 0, 0x9b00, 0x008f
-        // 16 bit data segment base=0 limit=0xffffffff (SEG32_MODE16BIG_DS)
-        .word 0xffff, 0, 0x9300, 0x008f
-rombios32_gdt_end:
-
-
-/****************************************************************
- * Interrupt entry points (continued)
- ****************************************************************/
-
         ORG 0xe3fe
         .global entry_13_official
 entry_13_official:
         jmp entry_13
 
-        ORG 0xe401
-        .type __fdpt, @object
-__fdpt:
-        // XXX - Fixed Disk Parameter Table
-        .space 16
+        // 0xe401 - OldFDPT in disk.c
 
         ORG 0xe6f2
         .global entry_19_official
 entry_19_official:
         jmp entry_19
 
-        ORG 0xe6f5
-.include "out/cbt.proc.16.s"
-        .text
+        // 0xe6f5 - BIOS_CONFIG_TABLE in misc.c
 
-        ORG 0xe729
-        .type __brgt, @object
-__brgt:
-        // XXX - Baud Rate Generator Table
-        .space 16
+        // 0xe729 - BaudTable in serial.c
 
         ORG 0xe739
         IRQ_ENTRY_ARG 14
@@ -549,9 +482,7 @@ __brgt:
         ORG 0xef57
         IRQ_ENTRY 0e
 
-        ORG 0xefc7
-.include "out/floppy_dbt.proc.16.s"
-        .text
+        // 0xefc7 - diskette_param_table in floppy.c
 
         ORG 0xefd2
         IRQ_ENTRY_ARG 17
@@ -564,11 +495,7 @@ __int10_0x0f:
         ORG 0xf065
         IRQ_ENTRY_ARG 10
 
-        ORG 0xf0a4
-        .type __int1d, @object
-__int1d:
-        // XXX - INT 1D - SYSTEM DATA - VIDEO PARAMETER TABLES
-        .space 0x58
+        // 0xf0a4 - VideoParams in misc.c
 
         ORG 0xf841
         .global entry_12_official
@@ -608,9 +535,7 @@ entry_18:
         pushl $_code32_handle_18
         jmp transition32
 
-        ORG 0xfa6e
-.include "out/font.proc.16.s"
-        .text
+        // 0xfa6e - vgafont8 in font.c
 
         ORG 0xfe6e
         IRQ_ENTRY_ARG 1a
@@ -618,16 +543,9 @@ entry_18:
         ORG 0xfea5
         IRQ_ENTRY 08
 
-        ORG 0xfef3
-__initvector:
-        // XXX - Initial Interrupt Vector Offsets Loaded by POST
-        .space 13
+        // 0xfef3 - InitVectors in misc.c
 
-        ORG 0xff00
-        .type __copyright, @object
-__copyright:
-        // XXX - BIOS_COPYRIGHT_STRING
-        .asciz "(c) 2002 MandrakeSoft S.A. Written by Kevin Lawton & the Bochs team."
+        // 0xff00 - BiosCopyright in misc.c
 
         ORG 0xff53
         .global dummy_iret_handler
@@ -642,20 +560,10 @@ dummy_iret_handler:
 reset_vector:
         ljmpw $SEG_BIOS, $post16
 
-        ORG 0xfff5
-        .type __biosdate, @object
-__biosdate:
-        // BIOS build date
-        .ascii "06/23/99"
-
-        ORG 0xfffe
-        .type __model_id, @object
-__model_id:
-        .byte CONFIG_MODEL_ID
-
-        .global bios_checksum
-        .type bios_checksum, @object
-bios_checksum:
-        .byte 0x00
+        // 0xfff5 - BiosDate in misc.c
+
+        // 0xfffe - BiosModelId in misc.c
+
+        // 0xffff - BiosChecksum in misc.c
 
         .end
diff --git a/src/serial.c b/src/serial.c
index 5eefaf3d..f9857e45 100644
--- a/src/serial.c
+++ b/src/serial.c
@@ -170,6 +170,9 @@ handle_14(struct bregs *regs)
     }
 }
 
+// XXX - Baud Rate Generator Table
+u8 BaudTable[16] VAR16FIXED(0xe729);
+
 
 /****************************************************************
  * LPT ports
diff --git a/src/system.c b/src/system.c
index 9bf4a5dc..ebb8d41d 100644
--- a/src/system.c
+++ b/src/system.c
@@ -1,4 +1,4 @@
-// 16bit system callbacks
+// Handler for int 0x15 "system" calls
 //
 // Copyright (C) 2008  Kevin O'Connor <kevin@koconnor.net>
 // Copyright (C) 2002  MandrakeSoft S.A.
@@ -269,10 +269,6 @@ handle_15e801(struct bregs *regs)
 // Info on e820 map location and size.
 struct e820entry *e820_list VAR16_32;
 int e820_count VAR16_32;
-// Amount of continuous ram under 4Gig
-u32 RamSize VAR16_32;
-// Amount of continuous ram >4Gig
-u64 RamSizeOver4G;
 
 static void
 handle_15e820(struct bregs *regs)
@@ -340,65 +336,3 @@ handle_15(struct bregs *regs)
     default:   handle_15XX(regs); break;
     }
 }
-
-// INT 12h Memory Size Service Entry Point
-void VISIBLE16
-handle_12(struct bregs *regs)
-{
-    debug_enter(regs, DEBUG_HDL_12);
-    regs->ax = GET_BDA(mem_size_kb);
-}
-
-// INT 11h Equipment List Service Entry Point
-void VISIBLE16
-handle_11(struct bregs *regs)
-{
-    debug_enter(regs, DEBUG_HDL_11);
-    regs->ax = GET_BDA(equipment_list_flags);
-}
-
-// INT 05h Print Screen Service Entry Point
-void VISIBLE16
-handle_05(struct bregs *regs)
-{
-    debug_enter(regs, DEBUG_HDL_05);
-}
-
-// INT 10h Video Support Service Entry Point
-void VISIBLE16
-handle_10(struct bregs *regs)
-{
-    debug_enter(regs, DEBUG_HDL_10);
-    // dont do anything, since the VGA BIOS handles int10h requests
-}
-
-void VISIBLE16
-handle_nmi()
-{
-    debug_isr(DEBUG_ISR_nmi);
-    BX_PANIC("NMI Handler called\n");
-}
-
-void
-mathcp_setup()
-{
-    dprintf(3, "math cp init\n");
-    // 80x87 coprocessor installed
-    SETBITS_BDA(equipment_list_flags, 0x02);
-    enable_hwirq(13, entry_75);
-}
-
-// INT 75 - IRQ13 - MATH COPROCESSOR EXCEPTION
-void VISIBLE16
-handle_75()
-{
-    debug_isr(DEBUG_ISR_75);
-
-    // clear irq13
-    outb(0, PORT_MATH_CLEAR);
-    // clear interrupt
-    eoi_pic2();
-    // legacy nmi call
-    u32 eax=0, flags;
-    call16_simpint(0x02, &eax, &flags);
-}
diff --git a/src/types.h b/src/types.h
index 5bf7634c..52e508bc 100644
--- a/src/types.h
+++ b/src/types.h
@@ -32,6 +32,8 @@ union u64_u32_u {
 # define VAR16 __attribute__((section(".data16." __FILE__ "." __stringify(__LINE__))))
 // Designate a variable as visible to both 32bit and 16bit code.
 # define VAR16_32 VAR16 __VISIBLE
+// Designate a variable at a specific 16bit address
+# define VAR16FIXED(addr) __aligned(1) __VISIBLE  __attribute__((section(".fixedaddr." __stringify(addr))))
 // Designate top-level assembler as 16bit only.
 # define ASM16(code) asm(".section .text.asm." __FILE__ "." __stringify(__LINE__) "\n\t" code)
 #else
@@ -39,6 +41,7 @@ union u64_u32_u {
 # define VISIBLE32 __VISIBLE
 # define VAR16 __attribute__((section(".discard.var16")))
 # define VAR16_32 VAR16 __VISIBLE __attribute__((weak))
+# define VAR16FIXED(addr) VAR16_32
 # define ASM16(code)
 #endif
 
diff --git a/src/util.h b/src/util.h
index 7492c558..6893b48f 100644
--- a/src/util.h
+++ b/src/util.h
@@ -184,4 +184,7 @@ void mtrr_setup(void);
 // romlayout.S
 void reset_vector() __attribute__ ((noreturn));
 
+// misc.c
+extern u8 BiosChecksum;
+
 #endif // util.h