diff options
Diffstat (limited to 'src/drivers/ao_fat.c')
| -rw-r--r-- | src/drivers/ao_fat.c | 101 |
1 files changed, 58 insertions, 43 deletions
diff --git a/src/drivers/ao_fat.c b/src/drivers/ao_fat.c index c0412380..65c5ea7c 100644 --- a/src/drivers/ao_fat.c +++ b/src/drivers/ao_fat.c @@ -136,7 +136,6 @@ ao_fat_entry_read(uint16_t cluster) if (!ao_fat_cluster_valid(cluster)) return 0xfff7; -// cluster -= 2; sector = cluster >> (SECTOR_SHIFT - 1); offset = (cluster << 1) & SECTOR_MASK; buf = ao_fat_sector_get(fat_start + sector); @@ -162,7 +161,6 @@ ao_fat_entry_replace(uint16_t cluster, uint16_t new_value) if (!ao_fat_cluster_valid(cluster)) return 0; -// cluster -= 2; sector = cluster >> (SECTOR_SHIFT - 1); offset = (cluster << 1) & SECTOR_MASK; buf = ao_fat_sector_get(fat_start + sector); @@ -203,8 +201,11 @@ ao_fat_free_cluster_chain(uint16_t cluster) /* * ao_fat_cluster_seek * - * Walk a cluster chain the specified distance and return what we find - * there. If distance is zero, return the provided cluster. + * The basic file system operation -- map a file cluster index to a + * partition cluster number. Done by computing the cluster number and + * then walking that many clusters from the first cluster. Returns + * 0xffff if we walk off the end of the file or the cluster chain + * is damaged somehow */ static uint16_t ao_fat_cluster_seek(uint16_t cluster, uint16_t distance) @@ -219,34 +220,6 @@ ao_fat_cluster_seek(uint16_t cluster, uint16_t distance) } /* - * ao_fat_sector_seek - * - * The basic file system operation -- map a file sector number to a - * partition sector number. Done by computing the cluster number and - * then walking that many clusters from the first cluster, then - * adding the sector offset from the start of the cluster. Returns - * 0xffffffff if we walk off the end of the file or the cluster chain - * is damaged somehow - */ -static uint32_t -ao_fat_sector_seek(uint16_t cluster, uint32_t sector) -{ - uint16_t distance; - uint16_t offset; - - distance = sector / sectors_per_cluster; - offset = sector % sectors_per_cluster; - - cluster = ao_fat_cluster_seek(cluster, distance); - - if (!ao_fat_cluster_valid(cluster)) - return 0xffffffff; - - /* Compute the sector within the partition and return it */ - return data_start + (uint32_t) (cluster-2) * sectors_per_cluster + offset; -} - -/* * ao_fat_setup_partition * * Load the boot block and find the first partition @@ -385,14 +358,51 @@ ao_fat_setup(void) static struct ao_fat_dirent ao_file_dirent; static uint32_t ao_file_offset; +static uint32_t ao_file_cluster_offset; +static uint16_t ao_file_cluster; static uint8_t ao_file_opened; static uint32_t -ao_fat_offset_to_sector(uint32_t offset) +ao_fat_current_sector(void) { - if (offset > ao_file_dirent.size) + uint16_t cluster_offset; + uint32_t sector_offset; + uint16_t sector_index; + uint16_t cluster; + + if (ao_file_offset > ao_file_dirent.size) return 0xffffffff; - return ao_fat_sector_seek(ao_file_dirent.cluster, offset >> SECTOR_SHIFT); + + sector_offset = ao_file_offset >> SECTOR_SHIFT; + + if (!ao_file_cluster) { + cluster_offset = sector_offset / sectors_per_cluster; + + cluster = ao_fat_cluster_seek(ao_file_dirent.cluster, cluster_offset); + if (!ao_fat_cluster_valid(cluster)) + return 0xffffffff; + ao_file_cluster = cluster; + ao_file_cluster_offset = cluster_offset * bytes_per_cluster; + } + + sector_index = sector_offset % sectors_per_cluster; + return data_start + (uint32_t) (ao_file_cluster-2) * sectors_per_cluster + sector_index; +} + +static void +ao_fat_set_offset(uint32_t offset) +{ + + if (offset == 0) { + ao_file_cluster = ao_file_dirent.cluster; + ao_file_cluster_offset = 0; + } + else if (offset < ao_file_cluster_offset || + ao_file_cluster_offset + bytes_per_cluster <= offset) + { + ao_file_cluster = 0; + } + ao_file_offset = offset; } /* @@ -576,7 +586,7 @@ ao_fat_open(char name[11], uint8_t mode) if (mode > AO_FAT_OPEN_READ && (dirent.attr & AO_FAT_FILE_READ_ONLY)) return -AO_FAT_EACCESS; ao_file_dirent = dirent; - ao_file_offset = 0; + ao_fat_set_offset(0); ao_file_opened = 1; return AO_FAT_SUCCESS; } @@ -620,6 +630,7 @@ ao_fat_creat(char name[11]) ao_fat_dirent_init(dent, entry, &ao_file_dirent); ao_fat_root_put(dent, entry, 1); ao_file_opened = 1; + ao_fat_set_offset(0); status = -AO_FAT_SUCCESS; break; } else { @@ -645,6 +656,7 @@ ao_fat_close(void) memset(&ao_file_dirent, '\0', sizeof (struct ao_fat_dirent)); ao_file_offset = 0; + ao_file_cluster = 0; ao_file_opened = 0; ao_bufio_flush(); return AO_FAT_SUCCESS; @@ -681,7 +693,7 @@ ao_fat_read(void *dst, int len) else this_time = SECTOR_SIZE - offset; - sector = ao_fat_offset_to_sector(ao_file_offset); + sector = ao_fat_current_sector(); if (sector == 0xffffffff) break; buf = ao_fat_sector_get(sector); @@ -695,7 +707,7 @@ ao_fat_read(void *dst, int len) ret += this_time; len -= this_time; dst_b += this_time; - ao_file_offset += this_time; + ao_fat_set_offset(ao_file_offset + this_time); } return ret; } @@ -731,7 +743,7 @@ ao_fat_write(void *src, int len) else this_time = SECTOR_SIZE - offset; - sector = ao_fat_offset_to_sector(ao_file_offset); + sector = ao_fat_current_sector(); if (sector == 0xffffffff) break; buf = ao_fat_sector_get(sector); @@ -745,7 +757,7 @@ ao_fat_write(void *src, int len) ret += this_time; len -= this_time; src_b += this_time; - ao_file_offset += this_time; + ao_fat_set_offset(ao_file_offset + this_time); } return ret; } @@ -762,20 +774,23 @@ ao_fat_write(void *src, int len) int32_t ao_fat_seek(int32_t pos, uint8_t whence) { + uint32_t new_offset = ao_file_offset; + if (!ao_file_opened) return -AO_FAT_EBADF; switch (whence) { case AO_FAT_SEEK_SET: - ao_file_offset = pos; + new_offset = pos; break; case AO_FAT_SEEK_CUR: - ao_file_offset += pos; + new_offset += pos; break; case AO_FAT_SEEK_END: - ao_file_offset = ao_file_dirent.size + pos; + new_offset = ao_file_dirent.size + pos; break; } + ao_fat_set_offset(new_offset); return ao_file_offset; } |