Added foundation code to initialize the PIT and create a 10ms jiffies

counter.

4 files changed, 90 insertions, 10 deletions

diff --git a/kernel/boot.s b/kernel/boot.s
index be68109..e41c0b2 100644
--- a/kernel/boot.s
+++ b/kernel/boot.s
@@ -1,5 +1,7 @@
 global kboot
+global register_isr
 extern kmain
+extern timer_init
 
 ; Multiboot header
 section .mboothdr
@@ -15,6 +17,7 @@ kboot:
   cli
   call flush_gdt
   call flush_idt
+  call timer_init
   call kmain
   cli
   hlt
@@ -80,13 +83,22 @@ idtp:
 int_handler:
   iret
 
+irq_handler:
+  iret
+
 flush_idt:
   push ebp
   mov ebp, esp
-  mov ecx, 256
+  mov ecx, 0
   mov edx, idt
 .loop:
   mov eax, int_handler
+  cmp ecx, 0x20
+  jl .skip
+  cmp ecx, 0x2f
+  jg .skip
+  mov eax, irq_handler
+.skip:
   mov [edx], ax
   mov word [edx+2], 0x08
   mov byte [edx+4], 0
@@ -94,8 +106,9 @@ flush_idt:
   shr eax, 16
   mov [edx+6], ax
   add edx, 8
-  dec ecx
-  jz .end
+  inc ecx
+  cmp ecx, 256
+  je .end
   jmp .loop
 .end:
   lidt [idtp]
@@ -104,6 +117,21 @@ flush_idt:
   pop ebp
   ret
 
+; void register_isr(uint8_t n, void *handler);
+register_isr:
+  push ebp
+  mov ebp, esp
+  mov edx, [ebp+8]
+  shl edx, 3
+  add edx, idt
+  mov eax, [ebp+12]
+  mov [edx], ax
+  add edx, 6
+  shr eax, 16
+  mov [edx], ax
+  pop ebp
+  ret
+
 pic_init:
   push ebp
   mov ebp, esp
diff --git a/kernel/con.c b/kernel/con.c
index 3b48de1..69c34e1 100644
--- a/kernel/con.c
+++ b/kernel/con.c
@@ -43,8 +43,8 @@ static void scroll_up(void) {
   cursorpos(pos);
 }
 
-/* must be called before any console output */
-void con_init(void) {
+/* clear the console and reset the cursor to the starting position */
+void con_clear(void) {
   int n = COLS * ROWS;
   uint8_t *p = vram;
 
@@ -57,6 +57,12 @@ void con_init(void) {
   cursorpos(0);
 }
 
+/* must be called before any console output */
+void con_init(void) {
+  /* clear the console */
+  con_clear();
+}
+
 /* write a zero-terminated string to console */
 int puts(char *s) {
   uint8_t *p = &vram[pos];
diff --git a/kernel/kmain.c b/kernel/kmain.c
index e31782c..5b10ee1 100644
--- a/kernel/kmain.c
+++ b/kernel/kmain.c
@@ -1,6 +1,16 @@
+#include <asm/io.h>
 #include <kernel/con.h>
+#include <stdint.h>
 
-extern int printf(char *fmt, ...);
+uint32_t ticks = 0;
+
+#define millis() \
+  (ticks * 10)
+
+void sleep(int ms) {
+  uint64_t t = millis() + ms;
+  while(millis() < t);
+}
 
 void kmain(void) {
   con_init();
@@ -8,8 +18,10 @@ void kmain(void) {
   printf("Kernel booting...\n");
   printf("Kernel booted!\n");
 
-  printf("Number: %s %04x\n", "test", 0x18C);
-  printf("Number: %s %04X\n", "test", 0x18C);
-  printf("Number: %s %#04x\n", "test", 0x18C);
-  printf("Number: %s %#04X\n", "test", 0x18C);
+  printf("PIC1 Mask: 0x%02x\n", inb(0x21));
+
+  while(1) {
+    sleep(500);
+    printf("Reliable 500ms tick!\n");
+  }
 }
diff --git a/kernel/timer.s b/kernel/timer.s
new file mode 100644
index 0000000..de01ea6
--- /dev/null
+++ b/kernel/timer.s
@@ -0,0 +1,34 @@
+global timer_init
+extern register_isr
+
+; TODO: move this someplace safe (not kmain.c)
+extern ticks
+
+tick_handler:
+  push ax
+  inc dword [ticks]
+  mov al, 0x20
+  out 0x20, al
+  pop ax
+  iret
+
+timer_init:
+  push ebp
+  mov ebp, esp
+  ; register the tick_handler
+  push tick_handler
+  push dword 0x20
+  call register_isr
+  add esp, 8
+  ; initialize the pit
+  mov ax, 0x36
+  out 0x43, al
+  mov ax, 0x2E9C ; 10ms tick interval
+  out 0x40, al
+  mov al, ah
+  out 0x40, al
+  in al, 0x21
+  and al, 0xFE
+  out 0x21, al
+  pop ebp
+  ret