From 93585dc4da3be099e1ffe7e757aa7caff2e1f013 Mon Sep 17 00:00:00 2001
From: Aiden Gall <aiden@aidengall.xyz>
Date: Tue, 14 May 2024 19:43:28 +0100
Subject: initial commit

---
 kernel/main.c | 83 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 83 insertions(+)
 create mode 100644 kernel/main.c

(limited to 'kernel/main.c')

diff --git a/kernel/main.c b/kernel/main.c
new file mode 100644
index 0000000..e69af30
--- /dev/null
+++ b/kernel/main.c
@@ -0,0 +1,83 @@
+#include <stdint.h>
+#include "util.h"
+
+#define VGA_WIDTH 80
+#define VGA_HEIGHT 25
+
+struct e820_entry {
+	uint64_t base;
+	uint64_t length;
+	uint32_t type;
+	uint32_t ext_attr;
+};
+
+static uint64_t *
+memsetu64(uint64_t *const dst, const uint64_t c, const uint64_t n)
+{
+	for (uint64_t i = 0; i < n; ++i) dst[i] = c;
+	return dst;
+}
+
+static uint16_t *
+print_hex(uint16_t *dst, uint64_t num)
+{
+	dst[0] = 0x0f00 | '0';
+	dst[1] = 0x0f00 | 'x';
+
+	dst += 2;
+
+	for (int i = 0; i < 16; ++i) {
+		uint16_t x = (num >> 60);
+
+		*(dst++) = 0x0f00 | (x < 0xa ? x+'0' : x+'a'-0xa);
+
+		num <<= 4;
+	}
+
+	return dst;
+}
+
+static uint16_t *
+puts(uint16_t *dst, const char *str)
+{
+	for (; *str; ++str, ++dst) *dst = 0x0f00|(*str);
+	return dst;
+}
+
+static uint16_t *
+print_e820_table(uint16_t *dst, const struct e820_entry *const entries, const uint32_t count)
+{
+	for (uint32_t i = 0; i < count; ++i, dst += VGA_WIDTH) {
+		uint16_t *cursor;
+
+		cursor = print_hex(dst, entries[i].base);
+
+		*(cursor++) = 0x0f00 | '-';
+
+		cursor = print_hex(cursor, entries[i].base + entries[i].length - 1);
+
+		++cursor;
+		cursor = puts(cursor, entries[i].type == 1 ? "available" : "reserved");
+	}
+
+	return dst;
+}
+
+void
+kmain(void)
+{
+	vga_cursor_hide();
+
+	uint16_t *const vga_memory = (uint16_t *)0xb8000;
+	memsetu64((uint64_t *)vga_memory, 0x0f200f200f200f20, (VGA_WIDTH*VGA_HEIGHT*sizeof(uint16_t))/sizeof(uint64_t));
+
+	puts(vga_memory, "ProvidenceOS v0.1");
+	puts(vga_memory+VGA_WIDTH*2, "e820 memory map:");
+
+	const uint32_t e820_size = *(uint32_t *)0xf000;
+	const struct e820_entry *const e820_mmap = (struct e820_entry *)0xf004;
+
+	print_e820_table(vga_memory+(VGA_WIDTH*3), e820_mmap, e820_size);
+
+	halt();
+}
-- 
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