structs.txt

一款MP3 Player Firmware 的原代码,非常有参考价值

function "fd_to_ptr" is always used to get memory location of
a file_info struct, so that (hopefully) it'll be painless to
later append more elements to it.

An array of 16 file_info's is statically allocated

struct file_info {     (24 bytes)
0	byte    flags;                  ;bit 0, set=open, clear=closed
					;bit 1, set=caching, clear=not caching
1	byte    unused0;
2	uint24	fcache_first_cluster_offset;
5	uint24	fcache_last_cluster_offset;
8	int16   first_cached_cluster;
10	int16	fcache_prev_cluster;
12	uint32  first_cluster_number;
16	int16	pos_block;		;block position within file
18	int16	pos_byte;		;byte offset within that block
20	byte    unused[4];
};



0A18: 01 00 030000 D70500
0A20: 1C01 1E01 0300 0100 1C01 0000 0000 0000

0	byte    flags;				= 01
1	byte    unused0;			= 00
2	uint24	fcache_first_cluster_offset;	= 000003
5	uint24	fcache_last_cluster_offset;	= 0005D7
8	int16   first_cached_cluster;		= 011C
10	int16	fcache_prev_cluster;		= 011E
12	uint32  first_cluster_number;		= 00010003
16	int16	pos_block;			= 011C
18	int16	pos_byte;			= 0000
20	byte    unused[4];			= 00000000




file_info.flags :





An array of ??? read requests is staticly allocated


struct read_request {
        uint32  lba_to_read;
        int16   block_to_read_into;
	int16	unused;
};

struct play_request {
        int16   block_to_play;
	int16	num_bytes_to_play;
};



An array of 8192 block_info's is allocated in the first
32 blocks of memory.  The function "block_desc_addr" is
used to map one of the 32 pages into 0xEXXX and return
the address of a particular block's block_info in dptr.



struct block_info {    (16 bytes)
0	int16   next_block;
2	byte	flags;
3	byte	unused;
	union user_info {
		struct fat_sector {
4			uint32  sector_offset;
8			byte    file_usage_mask[8];
		}
		struct cluster {
4			uint24  cluster_offset;
7			byte	block_offset;
8			int16	next_cluster;
10			int16	number_of_bytes;
12			uint32  cluster_number;
		}
		struct static_mem {
4			uint16	address;
		}
	}
};

0EF0 0100 01 00 50000000 02000000 00000000
07F0 0100 01 00 68000000 02000000 00000000
0F00 0100 01 00 78010000 02000000 00000000



flags (from block_info):

bit 3-0:  Block type
	0 = free
	1 = malloc'd by application
	2 = fat sector
	3 = fat cluster, first block
	C = fixed 8051 memory space
	F = unimplemented
bit 4: unused (zero)
bit 5: unused (zero)
bit 6: unused (zero)
bit 7: read_pending:
	0 = data is valid
	1 = read is pending, the block doesn't have valid data yet