Add preemptive multitasking

Makefile

@@ -1,6 +1,7 @@
 PLAT=i386
-C_SOURCES = $(wildcard kernel/*.c kernel/cpu/$(PLAT)/*.c kernel/cpu/*.c) 
-C_HEADERS = $(wildcard kernel/*.h kernel/cpu/$(PLAT)/*.h kernel/cpu/*.h) 
+TIMER_TYPE=$(shell cat psinfo/$(PLAT)/timer_type.txt)
+C_SOURCES = $(wildcard kernel/*.c kernel/cpu/$(PLAT)/*.c kernel/cpu/*.c kernel/timer/$(TIMER_TYPE)/*.c) 
+C_HEADERS = $(wildcard kernel/*.h kernel/cpu/$(PLAT)/*.h kernel/cpu/*.h kernel/timer/$(TIMER_TYPE)/*.h) 
 ASM = $(wildcard kernel/cpu/$(PLAT)/*.asm)
 S_ASM = $(wildcard kernel/cpu/$(PLAT)/*.s)
 LIBC_SOURCES = $(wildcard libc/*.c libc/*/*.c)

kernel/cpu/i386/isr.c

@@ -294,7 +294,7 @@ void irq_handler(registers_t* r) {
     port_byte_out(0x20,0x20); /* master */
     /* Handle the interrupt in a more modular way */
     if (irq_handlers[r->int_no-32] != NULL) {
-        isr_t handler = irq_handlers[r->int_no];
+        isr_t handler = irq_handlers[r->int_no-32];
         handler(r);
     }
 }

kernel/kernel.c

@@ -11,6 +11,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <tasking.h>
+#include "timer/timer.h"
 
 /**
  * REspresents a TAR file header
@@ -66,6 +67,7 @@ void kmain(struct multiboot_boot_header_tag* hdr) {
   asm volatile("sti");
   tasking_init();
   vga_init((char*)0xC00B8000);
+  timer_init(1000);
   read_initrd(tags);
   int pos=0;
   size_t datapos;
@@ -115,13 +117,14 @@ void kmain(struct multiboot_boot_header_tag* hdr) {
       copy_data(address_space,ptr,pheader.memsz,(void*)pheader.vaddr);
     }
     create_proc((void*)header.entry,address_space,NULL,NULL);
-    for (int i=0;i<4;i++) {
-      yield();
-    }
-    unblock_thread(1,0);
-    for (int i=0;i<4;i++) {
-      yield();
-    }
+    // for (int i=0;i<4;i++) {
+    //   yield();
+    // }
+    // unblock_thread(1,0);
+    // for (int i=0;i<4;i++) {
+    //   yield();
+    // }
+    // for (;;);
     exit(0);
   }
 }

kernel/timer/pit/timer.c

@@ -0,0 +1,26 @@
+#include "../../cpu/isr.h"
+#include "../../tasking.h"
+#include "../../cpu/serial.h"
+#include <cpu/ports.h>
+
+void timer_handler(registers_t* r);
+
+void timer_init(int freq) {
+  int div=1193180/freq;
+  if (div>65535) {
+    serial_printf("Frequency of %dHz too slow, min freq is 18 Hz\n");
+    div=65535;
+    freq=18;
+  if (div==0) {
+    serial_printf("Frequency of %dHz too slow, max freq is 1193180 Hz\n");
+    div=1;
+    freq=1193180;
+  }
+  } else {
+    serial_printf("Setting PIT to %dHz using divisor of %d\n",freq,div);
+  }
+  isr_register_handler(0,timer_handler);
+  port_byte_out(0x43,(div>>8)&0xFF);
+  port_byte_out(0x40,div&0xFF);
+  port_byte_out(0x40,0x2E);
+}

kernel/timer/timer.h

@@ -0,0 +1,14 @@
+/**
+ * \file
+*/
+
+#ifndef TIMER_H
+#define TIMER_H
+
+/**
+ * Initialize the timer
+ * \param freq The freqency to set the timer to
+*/
+void timer_init(int freq);
+
+#endif

kernel/timer_handler.c

@@ -0,0 +1,14 @@
+/**
+ * \file
+*/
+
+#include "tasking.h"
+#include "cpu/isr.h"
+
+/**
+ * Interrupt handler for the timer interrupt
+ * \param r The saved state of the CPU when the interrupt occured
+*/
+void timer_handler(registers_t* r) {
+  tasking_yield();
+}

psinfo/i386/timer_type.txt

@@ -0,0 +1 @@
+pit