Implement changing PIT frequency

ticks are now 1000.15 or so Hz

rust_experiments/src/lib.rs

@@ -38,12 +38,14 @@ pub extern fn rust_handle_timer() {
 }
 
 fn timer_callback(count: u64) {
-    if count % 4 == 0 {
+    if count % 1000  == 0 {
         checkerboard(vga_buffer::Color::White);
     }
-    if count % 4 == 2 {
+    if count % 1000 == 500 {
         checkerboard(vga_buffer::Color::LightCyan);
     }
+
+    vga_buffer::print_u32(count as u32, 0);
 }
 
 #[no_mangle]

rust_experiments/src/long_mode_init.asm

@@ -170,7 +170,7 @@ setup_IDT:
     ret
 
 setup_PIC:
-    mov al, 0xfc
+    mov al, 0xfc ;timer and keyboard, no more
     out byte 0x21, al
     mov al, 0xff
     out byte 0xa1, al
@@ -178,6 +178,20 @@ setup_PIC:
     ret
 
 setup_PIT:
+%define PIT_CH0 0x40
+%define PIT_MODE_CMD 0x43
+%define TIMER_CONSTANT 1193 ;generates ticks at 1000.15 Hz
+    cli
+
+    mov al, 0b00_11_010_0 ; channel 0, low-byte/hi-byte, rate generator
+    out PIT_MODE_CMD, al
+
+    mov ax, TIMER_CONSTANT
+    out PIT_CH0, al
+    mov al, ah
+    out PIT_CH0, al
+
+    sti
     ret
 
 idt64: