From 8a5fbdabb24250a76feed770bce64d7e3e4f61de Mon Sep 17 00:00:00 2001
From: Miguel <m.i@gmx.at>
Date: Tue, 21 Aug 2018 01:24:14 +0200
Subject: adding new pit code

---
 asm/asm.h |  4 +++-
 asm/pit.h | 25 +++++++++++++++++++++++++
 asm/pit.s | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 87 insertions(+), 1 deletion(-)
 create mode 100644 asm/pit.h
 create mode 100644 asm/pit.s

diff --git a/asm/asm.h b/asm/asm.h
index cc1d99d..8433e4e 100644
--- a/asm/asm.h
+++ b/asm/asm.h
@@ -1,9 +1,11 @@
 void pic_setup();
+
 void int_kb_handler();
 void int_mouse_handler();
 void int_default_handler();
-void int_clock_handler();
+
 void int_syscall_handler();
+
 void int_irq0();
 void int_irq1();
 void int_irq2();
diff --git a/asm/pit.h b/asm/pit.h
new file mode 100644
index 0000000..0bec3c4
--- /dev/null
+++ b/asm/pit.h
@@ -0,0 +1,25 @@
+/**
+ * @file
+ *
+ * PIT - Programmable Interval Timer
+ *
+ * config out timer on channel 0 : mode 2 (sys timer)
+ * * http://en.wikipedia.org/wiki/Intel_8253#Control_Word_Register
+ * * http://www.brokenthorn.com/Resources/OSDevPit.html
+ * int0 will be triggered ~25 times a second.
+ *
+ * The most magic is performed in pit_interrupt_handler which calls 
+ * the c function responsible for task switching doing vary bad ass 
+ * magic... 
+ */
+
+#include <stdint.h>
+
+/** Init PIT - 25 times a second*/
+void pit_init();
+
+/** install this interrupt handler to your Interrupt Vector Table */
+void pit_interrupt_handler();
+
+/** get number of ticks */
+uint32_t pit_get_ticks();
diff --git a/asm/pit.s b/asm/pit.s
new file mode 100644
index 0000000..ab8dcdb
--- /dev/null
+++ b/asm/pit.s
@@ -0,0 +1,59 @@
+.global pit_init
+.global pit_interrupt_handler
+.global pit_get_ticks
+
+ticks:
+.int 0
+
+pit_get_ticks:
+    
+    mov (ticks),%eax
+    ret
+
+pit_interrupt_handler:
+
+    // increase tick counter
+    push %eax
+    mov $ticks, %eax
+    incl (%eax)
+    pop %eax
+
+    ////
+
+    pusha          //Push all standard registers
+
+    mov %esp, %eax	//save current stack pointer (pointing to registers!)
+
+    movl $stack_top, %esp	//use stack from multiboot.s(16Kb)
+
+    // call our scheduler passing it the old stack addres (pointing to pushed registers (pusha))
+    push %eax   
+    call task_switch_next 
+
+    // the scheduler returned the new stack pointer (after taskswitch)
+    mov %eax, %esp   //Replace the stack with what the C code gave us
+
+    // acknowlege irq
+    mov $0x20,%al   
+    out %al,$0x20   
+    
+    popa           //Put the standard registers back
+
+    iret
+
+pit_init:
+
+    // configure ticking 25 times a second
+    // 1193180 / 25 = 47727.2
+    mov $47727, %dx
+
+    mov $0b00110100, %al
+    outb %al,$0x43
+
+    mov %dx,%ax
+
+    out %al, $0x40
+    xchg %ah,%al
+    out %al, $0x40
+
+    ret
-- 
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