Initializes PIC 8259 and PIT. Re-initializes GDT. Initializes IDT. Ad…

…ded interrupt handler. Re-factored code.

boot32.S

@@ -17,7 +17,7 @@
 
  .equ KERNEL_VIRT_ADDR, 0x80000000
  .equ KERNEL_PGDIR_ENTRY, (KERNEL_VIRT_ADDR >> 20)
- .equ STACK_SIZE, 0x1000
+ .equ STACK_SIZE, 0x2000
 
  .globl _start
 _start:

bootldr.S

@@ -18,6 +18,7 @@
  .equ E820_MAP_ADDR, 0x1008
  .equ PROTECTED_MODE_STACK, 0xf000
  .equ KERNEL_SECTORS, ((KERNEL_SIZE + 0x200 -1) / 0x200)
+ .equ PIT_FREQUENCY, 1000
 
  // machine boots in 16bit real mode
  .code16
@@ -27,6 +28,65 @@
 _start:
  movb %dl, boot_drive
 
+ // initialize PIC
+
+ // mask master and slave PICs
+ movb $0xff, %al
+ outb %al, $0x21
+ outb %al, $0xa1
+
+ // init PIC1
+ movb $0x11, %al
+ outb %al, $0x20
+
+ // map vector 0x20-0x27 for IRQ 0-7
+ movb $0x20, %al
+ outb %al, $0x21
+
+ // cascade slave at IRQ 2
+ movb $0x4, %al
+ outb %al, $0x21
+
+ // Regular EOI for PIC1
+ movb $0x1, %al
+ outb %al, $0x21
+
+ // init PIC2
+ movb $0x11, %al
+ outb %al, $0xa0
+
+ // map vector 0x28-0x2f for IRQ 8-15
+ movb $0x28, %al
+ outb %al, $0xa1
+
+ // inform PIC2 that IRQ2 is the connected at PIC1
+ movb $0x2, %al
+ outb %al, $0xa1
+
+ // manual EOI for PIC2
+ movb $0x1, %al
+ outb %al, $0xa1
+
+ // small delay
+ movw $0xffff, %cx
+1:
+ loop 1b
+
+ // unmask PIC1 and PIC2
+ xorb %al, %al
+ outb %al, $0x21
+ outb %al, $0xa1
+
+ // set PIT frequency
+ cli
+ movb $0x34, %al
+ outb %al, $0x43
+ movw PIT_FREQUENCY, %ax
+ outb %al, $0x40
+ shrw $8, %ax
+ outb %al, $0x40
+ sti
+
  // clear screen
  movb $0, %ah
  movb $3, %al
@@ -119,8 +179,13 @@ a20_line:
  xorw %ax, %ax
  movw %ax, 4(%si)
 
- // read enough sectors to load kernel
  movw $KERNEL_SECTORS, %ax
+
+ // check kernel can fit into existing memory
+ cmpw $160, %ax
+ ja kernel_too_big
+
+ // read enough sectors to load kernel
  movw %ax, 2(%si)
 
  // size of the disk packet
@@ -166,6 +231,8 @@ a20_line:
  orl $1, %eax
  movl %eax, %cr0
 
+ cli
+
  // jump to protected mode
  ljmpl $0x8,$protectedmodeaddress
 
@@ -177,13 +244,18 @@ lba_read_error:
  int $0x10
  jmp loop
 
+kernel_too_big:
+ // write 'B' in the screen to indicate kernel too big
+ movb $'X', %al
+ movb $0x0e, %ah
+ int $0x10
+ jmp loop
+
  // protected mode code
  .code32
 
 protectedmodeaddress:
 
- cli
-
  // data descriptor is located in 0x10 location of GDT
  movl $0x10, %eax
  movl %eax, %ds

setup32.c

@@ -0,0 +1,158 @@
+/*****************************************************************************/
+/* File: setup32.c */
+/* */
+/* Description: x86 32 bit GDT re-initialization code to enable IDT, LDT */
+/* and TSS */
+/* */
+/* Author: Shoily O Rahman <[email protected]> */
+/* */
+/* Date: Mar 25, 2020 */
+/* */
+/*****************************************************************************/
+
+#include "util.h"
+#include "system.h"
+#include "setup32.h"
+
+#define UNUSED(x) (void)(x)
+
+// GDT data
+struct gdt_entry __attribute__((aligned(8))) gdt[LAST_SEG*8];
+
+struct _gdt_desc {
+ unsigned short size;
+ struct gdt_entry *gdt;
+}__attribute__((packed));
+
+struct _gdt_desc __attribute__((aligned(8))) gdt_desc;
+
+// IDT data
+struct idt_entry __attribute__((aligned(8))) idt[256];
+
+struct _idt_desc {
+ unsigned short size;
+ struct idt_entry *idt;
+}__attribute__((packed));
+
+struct _idt_desc __attribute__((aligned(8))) idt_desc;
+
+void common_trap_handler();
+
+void irq_handler_0();
+void irq_handler_1();
+void irq_handler_2();
+void irq_handler_3();
+void irq_handler_4();
+void irq_handler_5();
+void irq_handler_6();
+void irq_handler_7();
+void irq_handler_8();
+void irq_handler_9();
+void irq_handler_10();
+void irq_handler_11();
+void irq_handler_12();
+void irq_handler_13();
+void irq_handler_14();
+void irq_handler_15();
+
+void trap_handler() {
+}
+
+
+__attribute__((regparm(0))) void common_interrupt_handler(int irq) {
+
+ UNUSED(irq);
+}
+
+__attribute__((regparm(0))) void common_sys_call_handler(int syscallnr) {
+
+ UNUSED(syscallnr);
+}
+
+//
+// Re-initializes GDT for kernel code and data segement selectors
+//
+
+void setupGDT32() {
+
+ // setup GDT data structure
+ memset(gdt, sizeof(gdt), 0);
+ gdt_desc.size = sizeof(gdt) - 1;
+ gdt_desc.gdt = gdt;
+
+ SET_KERNEL_CODE_SEGMENT(gdt, 0xfffff, 0);
+ SET_KERNEL_DATA_SEGMENT(gdt, 0xfffff, 0);
+
+ SET_USER_CODE_SEGMENT(gdt, 0xfffff, 0);
+ SET_USER_DATA_SEGMENT(gdt, 0xfffff, 0);
+
+ MFENCE;
+
+ // Re-initialize GDT
+ __asm__ __volatile__("movl $%0, %%eax;"
+ "lgdt (%%eax);"
+ "ljmpl %1, $reinitsegs;"
+ "reinitsegs:;"
+ "movl %2, %%eax;"
+ "movl %%eax, %%ds;"
+ "movl %%eax, %%es;"
+ "movl %%eax, %%ss;"
+ "movl %%eax, %%fs;"
+ "movl %%eax, %%gs;"
+ :
+ : "m" (gdt_desc), "i" (KERNEL_CODE_SEG), "i" (KERNEL_DATA_SEG)
+ : "%eax"
+ );
+}
+
+void setupIDT32() {
+
+ // setup IDT data structure
+ memset(idt, sizeof(idt), 0);
+ idt_desc.size = sizeof(idt) - 1;
+ idt_desc.idt = idt;
+
+
+ SET_TRAP_GATE(idt, 2, common_trap_handler);
+
+ SET_INTERRUPT_GATE(idt, 32, irq_handler_0);
+ SET_INTERRUPT_GATE(idt, 33, irq_handler_1);
+ SET_INTERRUPT_GATE(idt, 34, irq_handler_2);
+ SET_INTERRUPT_GATE(idt, 35, irq_handler_3);
+ SET_INTERRUPT_GATE(idt, 36, irq_handler_4);
+ SET_INTERRUPT_GATE(idt, 37, irq_handler_5);
+ SET_INTERRUPT_GATE(idt, 38, irq_handler_6);
+ SET_INTERRUPT_GATE(idt, 39, irq_handler_7);
+ SET_INTERRUPT_GATE(idt, 40, irq_handler_8);
+ SET_INTERRUPT_GATE(idt, 41, irq_handler_9);
+ SET_INTERRUPT_GATE(idt, 42, irq_handler_10);
+ SET_INTERRUPT_GATE(idt, 43, irq_handler_11);
+ SET_INTERRUPT_GATE(idt, 44, irq_handler_12);
+ SET_INTERRUPT_GATE(idt, 45, irq_handler_13);
+ SET_INTERRUPT_GATE(idt, 46, irq_handler_14);
+ SET_INTERRUPT_GATE(idt, 47, irq_handler_15);
+
+ MFENCE;
+
+ // Initialize IDT
+ __asm__ __volatile__("movl $%0, %%eax;"
+ "lidt (%%eax);"
+ "sti;"
+ ";"
+ :
+ : "m" (idt_desc)
+ : "%eax"
+ );
+
+}
+
+void setup32() {
+
+ init_pic_8259();
+ init_pit_frequency();
+
+ setupGDT32();
+ setupIDT32();
+
+ print_vga("Setup GDT and IDT done", true);
+}

x86_32.h → setup32.h

@@ -1,5 +1,5 @@
 /*****************************************************************************/
-/* File: x86_32.h  */
+/* File: setup32.h */
 /* */
 /* Description: Header file for x86 32 bit data structure for GDT, IDT, TSS */
 /* and related macros. */
@@ -10,8 +10,8 @@
 /* */
 /*****************************************************************************/
 
-#ifndef _X86_32_H
-#define _X86_32_H
+#ifndef _SETUP_32_H
+#define _SETUP_32_H
 
 #define USER_CODE_SEG 0x10
 #define USER_DATA_SEG 0x18
@@ -43,8 +43,8 @@ struct gdt_entry {
 struct idt_entry {
  unsigned short offset_low;
  unsigned short segment_selector;
- unsigned char unused;
 
+ unsigned char unused;
  unsigned char type:4;
  unsigned char s:1;
  unsigned char dpl:2;
@@ -144,6 +144,6 @@ struct tss_entry {
  SET_IDT_ENTRY(idt, index, 0, KERNEL_CODE_SEG, 0x5, 0, 1); \
  }
 
-void start32();
+void setup32();
 
 #endif

start.c

@@ -11,9 +11,9 @@
 /*****************************************************************************/
 
 #include "type.h"
-#include "common.h"
-#include "x86.h"
-#include "x86_32.h"
+#include "util.h"
+#include "system.h"
+#include "setup32.h"
 
 //
 // Start kernel routine
@@ -24,7 +24,7 @@ int start_kernel(void) {
  print_vga("XIS kernel started (v1.0)", true);
  print_vga("", true);
  dump_e820();
- start32();
+ setup32();
 
  return 0;
 }