Prex - FAT32

原本是打算將ELM FAT implementation移植到Prex上
然而因為Prex的Embedded VFS設計的緣故(該設計相當接近於VFS in Sun Unix),
若採用整合ELM FAT的方式需要相當的時間
而其中原因在於資料結構上的考量
因此就改為直接修改Prex本身具有的FAT 12/16以支援FAT32
如此還能針對FAT深入瞭解

而經過數日的奮戰
目前Prex 已經能夠操作 FAT32 檔案系統
也簡短地測試過, 檔案/目錄的新增移除是正常的
尚未支援用以輔助配置free block的 FSINFO以及長檔名的LFN(Long File Name)
有機會再把實做補上
由於處理FAT32的緣故, 研讀了些關於FS的相關資料
而先前所提到的書 File System Forensic Analysis 也幫助不少
另外下列資訊也有相當得助益

• Master Boot Record
• Microsoft FAT32 Spec
• The FAT File System
  

boot log如下:
Prex version 0.8.1 for arm-at2440ii (Feb 12 2009)
Free pages:
start end size
-------- -------- --------
00000000 - 00010000 64K
00033800 - 01c27000 28622K
01c39c00 - 04000000 36633K
used=142K free=65319K total=65461K
Time slice is 50 msec
IRQ10 attached priority=10
Clock rate: 1000 ticks/sec
Prex driver module built: Feb 12 2009
Calibrating delay loop... ok count=837
Initializing NULL device
Initializing Power Management
pm: Default power policy is performance mode
Initializing Zero device
Initializing Serial Console
UBRDIV0:0x23
IRQ28 attached priority=1
Initializing RAM disk
RAM disk at 0x01c270e0 (74K bytes)
Initializing SD card
Init. SD Freq. is 401256Hz

In idle
MMC check end!!

In SD ready

End id
RCA=0x9ffc
SD Frequency is 33304320Hz

In stand-by

****4bit bus****
SD disk
IRQ21 attached priority=2
Initializing TTY device
Driver initialized
Loading task:'boot'
Loading task:'proc'
Loading task:'fs'
Loading task:'exec'
Starting Bootstrap Server
Starting Process Server
Starting File System Server
Starting Exec Server
boot: Mounting file systems
VFS: Mounting ramfs dev= dir=/
VFS: Mounting devfs dev= dir=/dev
VFS: Mounting arfs dev=/dev/ram0 dir=/boot
VFS: Mounting fifofs dev= dir=/fifo
VFS: Mounting fatfs dev=/dev/card0 dir=/mnt/floppy
fatfs_mount device=/dev/card0
0 1 1 0 b 1f fd f7 3d 0 0 0 c3 42 1e 0
fatfs partition at sect: 3d
----- FAT 12/16/32 info ----- 3c673
drive:80
total_sectors:1983170
heads :32
serial :49984554
cluster size:8 sectors
fat_start :5d
root_start :2
data_start :f77
fat_type :FAT32
fat_eof :0xfffffff

boot: Run init process
Prex version 0.8.1 (arm-at2440ii)
[prex:/]# cat /mnt/floppy/champ.txt
fatfs_lookup: name=champ.txt
fat_lookup_denode: cl=0 name=champ.txt
fat_lookup_dirent: Ac
fat_lookup_dirent: found sec=3959
fatfs_lookup: cl=4
fatfs_read: vp=38e3c
Hello World!
fatfs_read: vp=38e3c
[prex:/]#