From 506f1691f1ca7b562d82ab6f2280b87d0e4af84c Mon Sep 17 00:00:00 2001 From: James Barnett Date: Sat, 25 May 2019 20:11:52 +0100 Subject: Add keyboard support --- kernel/global_descriptor_table.c | 50 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 50 insertions(+) create mode 100644 kernel/global_descriptor_table.c (limited to 'kernel/global_descriptor_table.c') diff --git a/kernel/global_descriptor_table.c b/kernel/global_descriptor_table.c new file mode 100644 index 0000000..16b99dc --- /dev/null +++ b/kernel/global_descriptor_table.c @@ -0,0 +1,50 @@ +extern void flush_gdt(); + +struct gdt_entry +{ + unsigned short limit_low; + unsigned short base_low; + unsigned char base_middle; + unsigned char access; + unsigned char granularity; + unsigned char base_high; +} __attribute__((packed)); + +struct gdt_ptr +{ + unsigned short limit; + unsigned int base; +} __attribute__((packed)); + +struct gdt_entry gdt[3]; +struct gdt_ptr gdt_pointer; + +void gdt_set_gate(int num, unsigned long base, unsigned long limit, unsigned char access, unsigned char gran) +{ + + gdt[num].base_low = (base & 0xFFFF); + gdt[num].base_middle = (base >> 16) & 0xFF; + gdt[num].base_high = (base >> 24) & 0xFF; + + gdt[num].limit_low = (limit & 0xFFFF); + gdt[num].granularity = ((limit >> 16) & 0x0F); + + gdt[num].granularity |= (gran & 0xF0); + gdt[num].access = access; +} + +void init_gdt() +{ + gdt_pointer.limit = (sizeof(struct gdt_entry) * 3) - 1; + gdt_pointer.base = (unsigned int) &gdt; + + // Values taken from bkerndev + // First GDT segment must be null + 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); + + flush_gdt(); +} \ No newline at end of file -- cgit v1.2.3