Replace bios with bootloader, don't use bootsector

Instead of using the bootsector to load a bootloader, just put the
bootloader in the ROM and call it a day. It looks for a file on the SD
card in the root directory named `kernel.bin` and loads it into memory.

This is not a perfect solution, as the kernel will grow larger and the
kernel load address will have to change. At this point I could add back
the bootloader, but that is for later.

Also the bootloader is just a copy of the kernel, so that can be trimmed
down a lot.

sw/bootloader/main.c

@@ -1,11 +1,63 @@
 #include <stdint.h>
+#include <conio.h>
+#include <string.h>
+#include <stdlib.h>
 
-#include "bios_calls.h"
-#include "uart.h"
+#include "devices/board_io.h"
+#include "devices/uart.h"
+#include "devices/mapper.h"
+#include "devices/sd_card.h"
+#include "filesystem/fat.h"
+#include "exec.h"
 
-//Should probably do this in asm
-void load_bootsect() {
-    uart_txb_block('A');
-    for (;;);
-    return;
-}
+#define KERNEL_LOAD_ADDR 0xD000
+
+uint8_t buf[512];
+
+int main() {
+	int i;
+	uint16_t rca;
+	char* filename;
+	uint32_t cluster;
+	uint8_t* kernel_load;
+
+	clrscr();
+	cprintf("boot\n");
+
+	for (i = 0; i < 16; i++){
+		//cprintf("Mapping %1xxxx to %2xxxx\n", i, i);
+		mapper_write(i, i);
+	}
+
+	cprintf("Enabling Mapper\n");
+	mapper_enable(1);
+
+	mapper_write(0x10, 0xd);
+	mapper_write(0x11, 0xe);
+	mapper_write(0x12, 0xf);
+
+	sd_init();
+
+	rca = sd_get_rca();
+	cprintf("rca: %x\n", rca);
+
+	sd_select_card(rca);
+
+	fat_init();
+
+	filename = (char*)malloc(FAT_MAX_FILE_NAME);
+
+	cluster = fat_parse_path_to_cluster("/kernel.bin");
+	for (kernel_load = (uint8_t*)KERNEL_LOAD_ADDR; cluster < FAT_CLUSTERMASK; kernel_load+=(8*512)) {
+		cprintf("cluster: %lx\n", cluster);
+		cprintf("Writing to %p\n", kernel_load);
+		fat_read_cluster(cluster, kernel_load);
+		cluster = fat_get_chain_value(cluster);
+	}
+
+	cprintf("Done!\n");
+
+	cprintf("Reset vector: %x\n", *((uint16_t*)0xfffc));
+
+	return 0;
+}