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209 lines
6.7 KiB
C
209 lines
6.7 KiB
C
/*
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* Copyright (C) 2018 bzt (bztsrc@github)
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*
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* Permission is hereby granted, free of charge, to any person
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* obtaining a copy of this software and associated documentation
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* files (the "Software"), to deal in the Software without
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* restriction, including without limitation the rights to use, copy,
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* modify, merge, publish, distribute, sublicense, and/or sell copies
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* of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be
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* included in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
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* HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
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* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
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* DEALINGS IN THE SOFTWARE.
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*
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*/
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#include "sd.h"
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#include "uart.h"
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// get the end of bss segment from linker
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extern unsigned char _end;
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unsigned int partitionlba;
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// the BIOS Parameter Block (in Volume Boot Record)
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typedef struct {
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char jmp[3];
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char oem[8];
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unsigned short bps;
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unsigned char spc;
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unsigned short rsc;
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unsigned char nf;
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unsigned short nr;
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unsigned short ts16;
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unsigned char media;
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unsigned short spf16;
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unsigned short spt;
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unsigned short nh;
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unsigned int hs;
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unsigned int ts32;
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unsigned int spf32;
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unsigned int flg;
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unsigned int rc;
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char vol[6];
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char fst[8];
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char dmy[20];
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char fst2[8];
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} __attribute__((packed)) bpb_t;
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// directory entry structure
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typedef struct {
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char name[8];
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char ext[3];
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char attr[9];
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unsigned short ch;
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unsigned int attr2;
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unsigned short cl;
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unsigned int size;
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} __attribute__((packed)) fatdir_t;
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/**
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* Get the starting LBA address of the first partition
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* so that we know where our FAT file system starts, and
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* read that volume's BIOS Parameter Block
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*/
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int fat_getpartition()
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{
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unsigned char *mbr=&_end;
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bpb_t *bpb=(bpb_t*)&_end;
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// read the partitioning table
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if(sd_readblock(0,&_end,1)) {
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// check magic
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if(mbr[510]!=0x55 || mbr[511]!=0xAA) {
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uart_puts("ERROR: Bad magic in MBR\n");
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return 0;
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}
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// check partition type
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if(mbr[0x1C2]!=0xE/*FAT16 LBA*/ && mbr[0x1C2]!=0xC/*FAT32 LBA*/) {
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uart_puts("ERROR: Wrong partition type\n");
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return 0;
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}
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partitionlba=*((unsigned int*)((unsigned long)&_end+0x1C6));
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// read the boot record
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if(!sd_readblock(partitionlba,&_end,1)) {
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uart_puts("ERROR: Unable to read boot record\n");
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return 0;
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}
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// check file system type. We don't use cluster numbers for that, but magic bytes
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if( !(bpb->fst[0]=='F' && bpb->fst[1]=='A' && bpb->fst[2]=='T') &&
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!(bpb->fst2[0]=='F' && bpb->fst2[1]=='A' && bpb->fst2[2]=='T')) {
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uart_puts("ERROR: Unknown file system type\n");
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return 0;
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}
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return 1;
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}
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return 0;
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}
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/**
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* Find a file in root directory entries
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*/
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unsigned int fat_getcluster(char *fn)
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{
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bpb_t *bpb=(bpb_t*)&_end;
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fatdir_t *dir=(fatdir_t*)(&_end+512);
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unsigned int root_sec, s;
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// find the root directory's LBA
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root_sec=((bpb->spf16?bpb->spf16:bpb->spf32)*bpb->nf)+bpb->rsc;
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//WARNING gcc generates bad code for bpb->nr, causing unaligned exception
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s=*((unsigned int*)&bpb->nf);
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s>>=8;
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s&=0xFFFF;
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s<<=5;
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// now s=bpb->nr*sizeof(fatdir_t));
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if(bpb->spf16==0) {
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// adjust for FAT32
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root_sec+=(bpb->rc-2)*bpb->spc;
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}
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// add partition LBA
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root_sec+=partitionlba;
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// load the root directory
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if(sd_readblock(root_sec,(unsigned char*)dir,s/512+1)) {
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// iterate on each entry and check if it's the one we're looking for
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for(;dir->name[0]!=0;dir++) {
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// is it a valid entry?
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if(dir->name[0]==0xE5 || dir->attr[0]==0xF) continue;
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// filename match?
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if(!__builtin_memcmp(dir->name,fn,11)) {
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uart_puts("FAT File ");
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uart_puts(fn);
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uart_puts(" starts at cluster: ");
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uart_hex(((unsigned int)dir->ch)<<16|dir->cl);
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uart_puts("\n");
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// if so, return starting cluster
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return ((unsigned int)dir->ch)<<16|dir->cl;
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}
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}
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uart_puts("ERROR: file not found\n");
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} else {
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uart_puts("ERROR: Unable to load root directory\n");
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}
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return 0;
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}
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/**
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* Read a file into memory
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*/
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char *fat_readfile(unsigned int cluster)
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{
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// BIOS Parameter Block
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bpb_t *bpb=(bpb_t*)&_end;
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// File allocation tables. We choose between FAT16 and FAT32 dynamically
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unsigned int *fat32=(unsigned int*)(&_end+bpb->rsc*512);
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unsigned short *fat16=(unsigned short*)fat32;
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// Data pointers
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unsigned int data_sec, s;
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unsigned char *data, *ptr;
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// find the LBA of the first data sector
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data_sec=((bpb->spf16?bpb->spf16:bpb->spf32)*bpb->nf)+bpb->rsc;
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//WARNING gcc generates bad code for bpb->nr, causing unaligned exception
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s=*((unsigned int*)&bpb->nf);
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s>>=8;
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s&=0xFFFF;
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s<<=5;
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if(bpb->spf16>0) {
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// adjust for FAT16
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data_sec+=(s+511)>>9;
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}
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// add partition LBA
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data_sec+=partitionlba;
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// dump important properties
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uart_puts("FAT Bytes per Sector: ");
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uart_hex(bpb->bps);
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uart_puts("\nFAT Sectors per Cluster: ");
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uart_hex(bpb->spc);
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uart_puts("\nFAT Number of FAT: ");
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uart_hex(bpb->nf);
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uart_puts("\nFAT Sectors per FAT: ");
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uart_hex((bpb->spf16?bpb->spf16:bpb->spf32));
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uart_puts("\nFAT Reserved Sectors Count: ");
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uart_hex(bpb->rsc);
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uart_puts("\nFAT First data sector: ");
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uart_hex(data_sec);
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uart_puts("\n");
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// load FAT table
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s=sd_readblock(partitionlba+1,(unsigned char*)&_end+512,(bpb->spf16?bpb->spf16:bpb->spf32)+bpb->rsc);
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// end of FAT in memory
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data=ptr=&_end+512+s;
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// iterate on cluster chain
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while(cluster>1 && cluster<0xFFF8) {
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// load all sectors in a cluster
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sd_readblock((cluster-2)*bpb->spc+data_sec,ptr,bpb->spc);
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// move pointer, sector per cluster * bytes per sector
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ptr+=bpb->spc*bpb->bps;
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// get the next cluster in chain
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cluster=bpb->spf16>0?fat16[cluster]:fat32[cluster];
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}
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return (char*)data;
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}
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