Add timer to count ticks

1 files changed, 28 insertions, 0 deletions

diff --git a/src/timer.c b/src/timer.c
new file mode 100644
index 0000000..73675dc
--- /dev/null
+++ b/src/timer.c
@@ -0,0 +1,28 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <go32.h>
+#include <dpmi.h>
+
+/* updates 18.2 times per second by default */
+volatile uint32_t ticks = 0;
+
+static _go32_dpmi_seginfo old_handler, new_handler;
+
+static void timer_handler()
+{
+    ticks++;
+}
+
+void timer_init()
+{
+    _go32_dpmi_get_protected_mode_interrupt_vector(0x1c, &old_handler);
+    new_handler.pm_offset = (unsigned long)timer_handler;
+    new_handler.pm_selector = _go32_my_cs();
+    _go32_dpmi_chain_protected_mode_interrupt_vector(0x1c, &new_handler);
+}
+
+void timer_free()
+{
+    if (_go32_dpmi_set_protected_mode_interrupt_vector(0x1c, &old_handler) == -1)
+        fprintf(stderr, "Failed to free the timer :(\n");
+}