diff --git a/kernel/Makefile b/kernel/Makefile
index 6ed77b6..df7ef58 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -15,7 +15,7 @@ export CXXFLAGS := -Wall -O2 -fno-rtti -fno-exceptions
 export LDFLAGS  := -T $(LDSCRIPT) -Map $(KERNEL).map
 export LDLIBS   := `$(CC) -print-libgcc-file-name`
 
-SUBDIRS         := boot mm lang isr
+SUBDIRS         := boot mm lang isr sys
 SUBDIRS_clean   := $(SUBDIRS:%=%.clean)
 
 .PHONY: all
diff --git a/kernel/boot/k_bootstrap.cc b/kernel/boot/k_bootstrap.cc
index 2607fd1..a5d573a 100644
--- a/kernel/boot/k_bootstrap.cc
+++ b/kernel/boot/k_bootstrap.cc
@@ -6,6 +6,7 @@
 #include "mm/mm.h"
 #include "mm/stack.h"
 #include "lang/kio.h"
+#include "isr/interrupts.h"
 
 #define DEBUG_LETTER(col,chr) *(u16_t *)(KERNEL_OFFSET + CONSOLE_MEMORY \
                                   + 160 * 8 + (col) * 2) \
@@ -48,6 +49,7 @@ u32_t k_bootstrap(mb_info_t * mb_info, u32_t mb_magic)
      */
     mm_bootstrap();
     stack_bootstrap();
+    interrupts_bootstrap();
     kio_bootstrap();
 
     return 0;
diff --git a/kernel/boot/k_main.cc b/kernel/boot/k_main.cc
index b9d4639..5ced9a7 100644
--- a/kernel/boot/k_main.cc
+++ b/kernel/boot/k_main.cc
@@ -1,12 +1,27 @@
 
 #include "lang/kio.h"
 #include "mm/mm.h"
+#include "sys/timer.h"
+#include "sys/pic.h"
+#include "isr/interrupts.h"
 
 extern "C" {
 
 void k_main()
 {
+    kprintf("Kernel load address: 0x%08x\n", KERNEL_CODE);
+    kprintf("Kernel code size: %d KB (%d bytes)\n",
+            (KERNEL_DATA - KERNEL_CODE) >> 10, KERNEL_DATA - KERNEL_CODE);
+    kprintf("Kernel data size: %d KB (%d bytes)\n",
+            (KERNEL_BSS - KERNEL_DATA) >> 10, KERNEL_BSS - KERNEL_DATA);
+    kprintf("Kernel bss size:  %d KB (%d bytes)\n",
+            (KERNEL_END - KERNEL_BSS) >> 10, KERNEL_END - KERNEL_BSS);
     mm_print_memory_map();
+    timer_init(KERNEL_TIMER_FREQ);
+    pic_remap(0x20, 0x28);
+    pic_mask1(0x0);
+    pic_mask2(0x0);
+    interrupts_enable();
 }
 
 } /* extern "C" */
diff --git a/kernel/include/hos_defines.h b/kernel/include/hos_defines.h
index 5ce31f6..42f9b55 100644
--- a/kernel/include/hos_defines.h
+++ b/kernel/include/hos_defines.h
@@ -18,10 +18,12 @@ extern "C" {
 #define CONSOLE_MEMORY          0xB8000
 
 extern  u8_t    _code;
+extern  u8_t    _data;
 extern  u8_t    _bss;
 extern  u8_t    _end;
 
 #define KERNEL_CODE (&_code)
+#define KERNEL_DATA (&_data)
 #define KERNEL_BSS  (&_bss)
 #define KERNEL_END  (&_end)
 
@@ -31,6 +33,8 @@ extern  u8_t    _end;
 
 #define KERNEL_STACK_TOP        0xF0000000
 
+#define KERNEL_TIMER_FREQ       1000
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/kernel/include/hos_types.h b/kernel/include/hos_types.h
index 9048d78..c1fd456 100644
--- a/kernel/include/hos_types.h
+++ b/kernel/include/hos_types.h
@@ -42,8 +42,8 @@ typedef struct
 
 typedef struct
 {
-    u16_t   length;
-    u32_t   phys_addr;
+    u16_t   limit;
+    u32_t   base;
 } __attribute__ ((packed)) gdtr_t;
 
 typedef gdtr_t idtr_t;
diff --git a/kernel/include/portio.h b/kernel/include/portio.h
old mode 100755
new mode 100644
diff --git a/kernel/isr/Makefile b/kernel/isr/Makefile
old mode 100755
new mode 100644
diff --git a/kernel/isr/interrupts.cc b/kernel/isr/interrupts.cc
old mode 100755
new mode 100644
index 43e71d4..9b243b1
--- a/kernel/isr/interrupts.cc
+++ b/kernel/isr/interrupts.cc
@@ -1,13 +1,47 @@
 
 #include "hos_types.h"
 #include "interrupts.h"
+#include "mm/mm.h"
+#include "lang/kio.h"
+#include "sys/pic.h"
+#include "sys/cpu.h"
 
 extern "C" {
 
-void isr(u8_t int_num, int_stack_t * int_stack)
+idtr_t idtr;
+
+void isr(u8_t int_num, int_stack_t * istack)
 {
     switch (int_num)
     {
+    case 0x20:                  /* timer interrupt */
+        (*(u16_t *)CONSOLE_MEMORY)++;
+        pic_eoi();
+        break;
+    case 0x21:
+        /* TODO: keyboard hook */
+        pic_eoi();
+        break;
+    default:
+        kputs("--------------------------------------------------------------------------------");
+        kprintf("Unhandled Interrupt #%d\n", int_num);
+        kprintf("    ds: 0x%08x     es: 0x%08x     fs: 0x%08x     gs: 0x%08x\n",
+                istack->ds, istack->es, istack->fs, istack->gs);
+        kprintf("   eax: 0x%08x    ebx: 0x%08x    ecx: 0x%08x    edx: 0x%08x\n",
+                istack->eax, istack->ebx, istack->ecx, istack->edx);
+        kprintf("   ebp: 0x%08x    esi: 0x%08x    edi: 0x%08x eflags: 0x%08x\n",
+                istack->ebp, istack->esi, istack->edi, istack->eflags);
+        kprintf("    cs: 0x%08x    eip: 0x%08x     ss: 0x%08x    esp: 0x%08x\n",
+                istack->cs, istack->eip, istack->ss, istack->esp);
+        kprintf("   cr0: 0x%08x    cr2: 0x%08x    cr3: 0x%08x\n",
+                read_cr0(), read_cr2(), read_cr3());
+        kprintf(" Error: 0x%08x (%d)\n", istack->error, istack->error);
+        kputs("--------------------------------------------------------------------------------");
+
+        kprintf("Halting!\n");
+        for (;;)
+            ;
+        break;
     }
 }
 
@@ -15,5 +49,59 @@ void isr(u8_t int_num, int_stack_t * int_stack)
 
 void interrupts_bootstrap()
 {
-    /* TODO: set up IDTR, IDT */
+    u32_t idt_base = mm_early_page_alloc();
+    u64_t * idt = (u64_t *) (idt_base + KERNEL_OFFSET);
+    idt[0]  = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_0,  0);
+    idt[1]  = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_1,  0);
+    idt[2]  = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_2,  0);
+    idt[3]  = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_3,  0);
+    idt[4]  = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_4,  0);
+    idt[5]  = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_5,  0);
+    idt[6]  = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_6,  0);
+    idt[7]  = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_7,  0);
+    idt[8]  = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_8,  0);
+    idt[9]  = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_9,  0);
+    idt[10] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_10, 0);
+    idt[11] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_11, 0);
+    idt[12] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_12, 0);
+    idt[13] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_13, 0);
+    idt[14] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_14, 0);
+    idt[15] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_15, 0);
+    idt[16] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_16, 0);
+    idt[17] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_17, 0);
+    idt[18] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_18, 0);
+    idt[19] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_19, 0);
+    idt[20] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_20, 0);
+    idt[21] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_21, 0);
+    idt[22] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_22, 0);
+    idt[23] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_23, 0);
+    idt[24] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_24, 0);
+    idt[25] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_25, 0);
+    idt[26] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_26, 0);
+    idt[27] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_27, 0);
+    idt[28] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_28, 0);
+    idt[29] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_29, 0);
+    idt[30] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_30, 0);
+    idt[31] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_31, 0);
+    idt[32] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_32, 0);
+    idt[33] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_33, 0);
+    idt[34] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_34, 0);
+    idt[35] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_35, 0);
+    idt[36] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_36, 0);
+    idt[37] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_37, 0);
+    idt[38] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_38, 0);
+    idt[39] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_39, 0);
+    idt[40] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_40, 0);
+    idt[41] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_41, 0);
+    idt[42] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_42, 0);
+    idt[43] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_43, 0);
+    idt[44] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_44, 0);
+    idt[45] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_45, 0);
+    idt[46] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_46, 0);
+    idt[47] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_47, 0);
+    idt[48] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_48, 0);
+    idt[49] = MAKE_IDT_DESCRIPTOR(KERNEL_CODE_SEGMENT, isr_49, 0);
+    idtr.base = idt_base;
+    idtr.limit = 49 * sizeof(idt[0]) - 1;
+    __asm__ __volatile__ ("lidt (idtr)");
 }
diff --git a/kernel/isr/interrupts.h b/kernel/isr/interrupts.h
index 608de31..93eb147 100644
--- a/kernel/isr/interrupts.h
+++ b/kernel/isr/interrupts.h
@@ -8,10 +8,72 @@ extern "C" {
 
 void isr(u8_t int_num, int_stack_t * int_stack);
 
+extern void isr_0();
+extern void isr_1();
+extern void isr_2();
+extern void isr_3();
+extern void isr_4();
+extern void isr_5();
+extern void isr_6();
+extern void isr_7();
+extern void isr_8();
+extern void isr_9();
+extern void isr_10();
+extern void isr_11();
+extern void isr_12();
+extern void isr_13();
+extern void isr_14();
+extern void isr_15();
+extern void isr_16();
+extern void isr_17();
+extern void isr_18();
+extern void isr_19();
+extern void isr_20();
+extern void isr_21();
+extern void isr_22();
+extern void isr_23();
+extern void isr_24();
+extern void isr_25();
+extern void isr_26();
+extern void isr_27();
+extern void isr_28();
+extern void isr_29();
+extern void isr_30();
+extern void isr_31();
+extern void isr_32();
+extern void isr_33();
+extern void isr_34();
+extern void isr_35();
+extern void isr_36();
+extern void isr_37();
+extern void isr_38();
+extern void isr_39();
+extern void isr_40();
+extern void isr_41();
+extern void isr_42();
+extern void isr_43();
+extern void isr_44();
+extern void isr_45();
+extern void isr_46();
+extern void isr_47();
+extern void isr_48();
+extern void isr_49();
+
 #ifdef __cplusplus
 }
 #endif
 
+#define MAKE_IDT_DESCRIPTOR(selector, offset, dpl) \
+    (u64_t) ( ( (((u64_t) offset) & 0xFFFF0000ull) << 32 )  /* offset 31:16 */ \
+            | ( ( (u64_t) 0x1ull) << 47 )                   /* present */      \
+            | ( (((u64_t) dpl) & 0x3) << 45 )               /* DPL */          \
+            | ( ( (u64_t) 0xEull) << 40 )                   /* TODO: gate? */  \
+            | ( (((u64_t) selector) & 0xFFFFull) << 16 )    /* selector */     \
+            | ( (((u64_t) offset) & 0x0000FFFFull) ) )      /* offset 15:0 */
+
 void interrupts_bootstrap();
 
+#define interrupts_enable() __asm__ __volatile__ ("sti");
+#define interrupts_disable() __asm__ __volatile__ ("cli");
+
 #endif
diff --git a/kernel/isr/isr.asm b/kernel/isr/isr.asm
index 4c3a8cc..d57917c 100644
--- a/kernel/isr/isr.asm
+++ b/kernel/isr/isr.asm
@@ -33,8 +33,7 @@ isr_common:
 
     push    esp                     ; pointer to interrupt stack
     push    eax                     ; interrupt number
-; TODO: uncomment when isr() is defined so the build won't break
-;    call    isr
+    call    isr
     pop     eax                     ; restore stack pointer (this is shorter
     pop     eax                     ; than "add esp, 8" and "lea esp, [esp+8]")
 
diff --git a/kernel/link.ld b/kernel/link.ld
index 60a6108..c9c17cc 100644
--- a/kernel/link.ld
+++ b/kernel/link.ld
@@ -12,6 +12,11 @@ SECTIONS
         *(.rodata*)
         . = ALIGN(4096);
     }
+    .other : {
+        *(.eh_*)
+        *(.rel*)
+        . = ALIGN(4096);
+    }
     .data : {
         data = .; _data = .; __data = .;
         *(.data*)
diff --git a/kernel/mm/mm.cc b/kernel/mm/mm.cc
index fc61054..e8422ff 100644
--- a/kernel/mm/mm.cc
+++ b/kernel/mm/mm.cc
@@ -6,6 +6,7 @@
 #include "boot/k_early_panic.h"
 #include "lang/string.h"
 #include "lang/kio.h"
+#include "sys/cpu.h"
 
 #define MM_MAX_MMAP_ENTRIES 64
 
@@ -148,10 +149,10 @@ void mm_bootstrap()
     u32_t gdt_base = mm_early_page_alloc();
     mm_gdt = (u64_t *) ((u32_t) gdt_base + (u32_t) KERNEL_OFFSET);
     mm_gdt[0] = 0x0ull;
-    mm_gdt[1] = MAKE_DESCRIPTOR(0, 0xFFFFF, 1, 0, 1, 1);
-    mm_gdt[2] = MAKE_DESCRIPTOR(0, 0xFFFFF, 1, 0, 1, 0);
-    mm_gdtr.length = 3*sizeof(mm_gdt[0]) - 1;
-    mm_gdtr.phys_addr = gdt_base;
+    mm_gdt[1] = MAKE_DESCRIPTOR(0, 0xFFFFF, 1, 0, 1, 1);    /* kernel code */
+    mm_gdt[2] = MAKE_DESCRIPTOR(0, 0xFFFFF, 1, 0, 1, 0);    /* kernel data */
+    mm_gdtr.limit = 3 * sizeof(mm_gdt[0]) - 1;
+    mm_gdtr.base = gdt_base;
 
     /* set the page directory base register */
     set_cr3(page_directory);
diff --git a/kernel/mm/mm.h b/kernel/mm/mm.h
index cd6af87..a5111bf 100644
--- a/kernel/mm/mm.h
+++ b/kernel/mm/mm.h
@@ -6,6 +6,9 @@
 #include "hos_defines.h"
 #include "multiboot.h"
 
+#define KERNEL_CODE_SEGMENT 0x08
+#define KERNEL_DATA_SEGMENT 0x10
+
 typedef u32_t pagedirectory_entry_t;
 
 #define NUM_PAGETABLE_ENTRIES (PAGE_SIZE / sizeof(pagedirectory_entry_t))
@@ -29,9 +32,6 @@ int mm_map(u32_t virtual_address, u32_t physical_address,
 u32_t mm_early_page_alloc();
 u32_t mm_page_alloc();
 
-#define set_cr3(address) \
-    __asm__ __volatile__ ("movl %0, %%cr3" : : "r" (address));
-
 /* http://courses.ece.illinois.edu/ece391/references/descriptors.pdf */
 /* granularity: 0: limit in bytes; 1: limit in pages */
 /* dpl: 0: system mode; 3: user mode */
diff --git a/kernel/mm/stack.cc b/kernel/mm/stack.cc
old mode 100755
new mode 100644
diff --git a/kernel/mm/stack.h b/kernel/mm/stack.h
old mode 100755
new mode 100644
diff --git a/kernel/sys/Makefile b/kernel/sys/Makefile
new file mode 100644
index 0000000..cae81d7
--- /dev/null
+++ b/kernel/sys/Makefile
@@ -0,0 +1,2 @@
+
+include $(HOS_TOPLEVEL)/subdir.mak
diff --git a/kernel/sys/cpu.h b/kernel/sys/cpu.h
new file mode 100644
index 0000000..76ff655
--- /dev/null
+++ b/kernel/sys/cpu.h
@@ -0,0 +1,34 @@
+
+#ifndef CPU_H
+#define CPU_H
+
+#include "hos_types.h"
+
+static u32_t read_cr0()
+{
+    u32_t val;
+    __asm__ __volatile__ ("movl %%cr0, %0" : "=r" (val));
+    return val;
+}
+
+static u32_t read_cr2()
+{
+    u32_t val;
+    __asm__ __volatile__ ("movl %%cr2, %0" : "=r" (val));
+    return val;
+}
+
+static u32_t read_cr3()
+{
+    u32_t val;
+    __asm__ __volatile__ ("movl %%cr3, %0" : "=r" (val));
+    return val;
+}
+
+#define set_cr0(val) \
+    __asm__ __volatile__ ("movl %0, %%cr0" : : "r" (val));
+
+#define set_cr3(val) \
+    __asm__ __volatile__ ("movl %0, %%cr3" : : "r" (val));
+
+#endif
diff --git a/kernel/sys/pic.cc b/kernel/sys/pic.cc
new file mode 100644
index 0000000..320e26e
--- /dev/null
+++ b/kernel/sys/pic.cc
@@ -0,0 +1,29 @@
+
+#include "pic.h"
+#include "portio.h"
+
+/*
+ * Re-maps the Programmable Interrupr Controllers
+ * so IRQ0->pic1 base address, IRG8->pic2 base address
+ */
+void pic_remap(u8_t base1, u8_t base2)
+{
+    u8_t    a1, a2;
+
+    a1 = inportb(PIC1_DATA);        /* 0x21 */
+    a2 = inportb(PIC2_DATA);        /* 0xA1 */
+
+    outportb(PIC1_COMMAND, ICW1_INIT+ICW1_ICW4); /* 0x20, 0x10+0x01 00010001b */
+    outportb(PIC2_COMMAND, ICW1_INIT+ICW1_ICW4); /* 0xA0, 0x10+0x01 00010001b */
+    outportb(PIC1_DATA, base1);     /* 0x21, pic1 */
+    outportb(PIC2_DATA, base2);     /* 0xA1, pic2 */
+    outportb(PIC1_DATA, 4);         /* 0x21, 0x04 00000100b */
+    outportb(PIC2_DATA, 2);         /* 0xA1, 0x02 00000010b */
+    outportb(PIC1_DATA, ICW4_8086); /* 0x21, 0x01 00000001b */
+    outportb(PIC2_DATA, ICW4_8086); /* 0xA1, 0x01 00000001b */
+
+    outportb(PIC1_DATA, a1);        /* 0x21 */
+    outportb(PIC2_DATA, a2);        /* 0xA1 */
+}
+
+
diff --git a/kernel/sys/pic.h b/kernel/sys/pic.h
new file mode 100644
index 0000000..1b793a9
--- /dev/null
+++ b/kernel/sys/pic.h
@@ -0,0 +1,46 @@
+
+#ifndef PIC_H
+#define PIC_H
+
+#include "hos_types.h"
+#include "portio.h"
+
+#define PIC1            0x20
+#define PIC2            0xA0
+#define PIC1_COMMAND    PIC1
+#define PIC1_DATA       (PIC1+1)
+#define PIC2_COMMAND    PIC2
+#define PIC2_DATA       (PIC2+1)
+#define PIC_EOI         0x20
+
+#define ICW1_ICW4       0x01            /* ICW4 (not) needed */
+#define ICW1_SINGLE     0x02            /* Single (cascade) mode */
+#define ICW1_INTERVAL4  0x04            /* Call address interval 4 (8) */
+#define ICW1_LEVEL      0x08            /* Level triggered (edge) mode */
+#define ICW1_INIT       0x10            /* Initialization - required! */
+
+#define ICW4_8086       0x01            /* 8086/88 (MCS-80/85) mode */
+#define ICW4_AUTO       0x02            /* Auto (normal) EOI */
+#define ICW4_BUF_SLAVE  0x08            /* Buffered mode/slave */
+#define ICW4_BUF_MASTER 0x0C            /* Buffered mode/master */
+#define ICW4_SFNM       0x10            /* Special fully nested (not) */
+
+void pic_remap(u8_t base1, u8_t base2);
+
+/* Masks interrupts on first Programmable Interrupt Controller */
+#define pic_mask1(mask) outportb(PIC1_DATA, mask) /* 0x21, maskfield *OCW1* */
+
+/* Masks interrupts on second Programmable Interrupt Controller */
+#define pic_mask2(mask) outportb(PIC2_DATA, mask) /* 0xA1, maskfield *OCW1* */
+
+/* Signals an End Of Interrupt signal to the first PIC */
+#define pic_eoi() outportb(0x20, 0x20)
+
+/* Signals an End Of Interrupt signal to both the second and first PIC unit */
+static inline void pic_eoi2()
+{
+        outportb(0xA0, 0x20);
+        outportb(0x20, 0x20);
+}
+
+#endif
diff --git a/kernel/sys/timer.cc b/kernel/sys/timer.cc
new file mode 100644
index 0000000..baa002b
--- /dev/null
+++ b/kernel/sys/timer.cc
@@ -0,0 +1,12 @@
+
+#include "timer.h"
+#include "portio.h"
+
+void timer_init(u32_t freq)
+{
+    /* how many ticks the PIT must wait before issuing an interrupt */
+    u32_t wait = 1193180 / freq;
+    outportb(0x43, 0x34);
+    outportb(0x40, wait);       /* LSB */
+    outportb(0x40, wait >> 8);  /* MSB */
+}
diff --git a/kernel/sys/timer.h b/kernel/sys/timer.h
new file mode 100644
index 0000000..c2e76af
--- /dev/null
+++ b/kernel/sys/timer.h
@@ -0,0 +1,9 @@
+
+#ifndef TIMER_H
+#define TIMER_H
+
+#include "hos_types.h"
+
+void timer_init(u32_t freq);
+
+#endif