127 lines
2.9 KiB
C
127 lines
2.9 KiB
C
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#include <stdint.h>
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#include <unistd.h>
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#include <string.h>
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#include "io.h"
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struct directory_entry {
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uint8_t file_name[8];
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uint8_t extension[3];
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uint8_t file_attributes;
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uint8_t reserved1;
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uint8_t ctime_ms;
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uint8_t ctime_hms[2];
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uint8_t ctime_date[2];
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uint8_t atime_date[2];
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uint8_t ea_index[2];
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uint8_t mtime_hms[2];
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uint8_t mtime_date[2];
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uint8_t first_cluster[2];
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uint8_t file_size[4];
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};
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int fat12_mkfs(int fd, uint32_t bytes) {
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uint8_t mbr[512];
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const uint16_t sector_size = 512;
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const uint8_t cluster_size = 8; // 4 kiB cluster sizes match flash erase block size
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// XXX What happens if this is an even multiple of sectors?
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uint32_t fat_size = 1 + ((((bytes * 3) / sector_size) / cluster_size) / 2);
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memset(mbr, 0, sizeof(mbr));
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// jmp instruction
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mbr[0] = 0xeb;
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mbr[1] = 0x3c;
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mbr[2] = 0x90;
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// OEM name
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memcpy(mbr+3, "Fomu MBR", 8);
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// Bytes per sector (512)
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fat12_write_u16(mbr + 0x0b, sector_size);
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// Sectors per cluster (8), so cluster is 512 * 8
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mbr[0x0d] = cluster_size;
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// Reserved sector count (8 sectors, to pad things to 4096-byte boundaries)
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fat12_write_u16(mbr + 0x0e, cluster_size);
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// Number of FATs (1)
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mbr[0x10] = 1;
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// Maximum number of root directory entries (16)
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fat12_write_u16(mbr + 0x11, 32);
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// Total number of 512-byte sectors
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fat12_write_u16(mbr + 0x13, bytes / sector_size);
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// Type of media (0xf8 == fixed disk)
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mbr[0x15] = 0xf8;
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// Sectors per FAT
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fat12_write_u16(mbr + 0x16, fat_size);
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// Sectors per track
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fat12_write_u16(mbr + 0x18, 32);
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// Number of heads
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fat12_write_u16(mbr + 0x1a, 64);
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// Hidden sectors
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mbr[0x1c] = 0x00;
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mbr[0x1d] = 0x00;
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mbr[0x1e] = 0x00;
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mbr[0x1f] = 0x00;
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// Total number of sectors (unused, since we put it in 0x13)
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mbr[0x20] = 0;
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mbr[0x21] = 0;
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mbr[0x22] = 0;
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mbr[0x23] = 0;
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// BIOS drive
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mbr[0x24] = 0x80;
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// Unused
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mbr[0x25] = 0;
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// Boot signature
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mbr[0x26] = 0x29;
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// Serial number
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mbr[0x27] = 0xf0;
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mbr[0x28] = 0xb0;
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mbr[0x29] = 0x00;
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mbr[0x2a] = 0x07;
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// Volume Name
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memcpy(mbr + 0x2b, "Fomu ", 11);
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// Filesystem
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memcpy(mbr + 0x36, "FAT12 ", 8);
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// Signature
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mbr[0xfe] = 0x55;
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mbr[0xff] = 0xaa;
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// Write MBR to disk
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if (pang_write(fd, mbr, sizeof(mbr)) != sizeof(mbr)) {
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return -1;
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}
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memset(mbr, 0, sizeof(mbr));
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// The first two clusters in the FAT are reserved, and must be 0xff
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fat12_set_cluster(mbr, 0, 0xff8); // 0xff8 instead of 0xfff indicates "Hard Disk"
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fat12_set_cluster(mbr, 1, 0xfff); // 0xfff is reserved value
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// Root directory is only one cluster
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fat12_set_cluster(mbr, 2, 0xfff);
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if (pang_write(fd, mbr, sizeof(mbr)) != sizeof(mbr)) {
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return -1;
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}
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return 0;
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}
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