first real commit

1 files changed, 33 insertions, 0 deletions

diff --git a/kernel/gdt.c b/kernel/gdt.c
new file mode 100644
index 0000000..f9b2d86
--- /dev/null
+++ b/kernel/gdt.c
@@ -0,0 +1,33 @@
+#include "gdt.h"
+
+static void gdt_set_gate(int idx, uint32_t base, uint32_t limit, uint8_t access, uint8_t gran)
+{
+    /* Setup the descriptor base address */
+    gdt[idx].base_low = (base & 0xFFFF);
+    gdt[idx].base_middle = (base >> 16) & 0xFF;
+    gdt[idx].base_high = (base >> 24) & 0xFF;
+
+    /* Setup the descriptor limits */
+    gdt[idx].limit_low = (limit & 0xFFFF);
+    gdt[idx].granularity = ((limit >> 16) & 0x0F);
+
+    /* Finally, set up the granularity and access flags */
+    gdt[idx].granularity |= (gran & 0xF0);
+    gdt[idx].access = access;
+}
+
+void gdt_init(void)
+{
+    gp.limit = (sizeof(struct gdt_entry) * sizeof(gdt)/sizeof(gdt[0])) - 1;
+    gp.base = (uint32_t)&gdt;
+
+    gdt_set_gate(0, 0, 0, 0, 0);
+
+    /* code segment */
+    gdt_set_gate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF);
+
+    /* data segment */
+    gdt_set_gate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);
+
+    gdt_flush((uint32_t)&gp);
+}