Analog Devices EE196 Application Notes
Engineer To Engineer Note EE-196
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Technical Notes on using Analog Devices' DSP components and development tools
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ADSP-BF535 Blackfin® EZ-KIT Lite™ CompactFlash® Interface
Contributed by Hiren Desai June 4, 2003
Introduction
CompactFlash® storage cards provide the
capability to easily transfer/store all types of
digital information, such as data, audio, and
images, between large varieties of digital
systems. CompactFlash cards are high density
(up to 1Gbytes of nonvolatile storage memory!),
removable (i.e. hot-swappable), and very
compact in size. CF™ cards can be used as
memory storage devices for digital imaging,
video, audio, PDAs, etc. but they can also be
extended for I/O communications applications
such as modems, Ethernet controllers, laser
scanners, BlueTooth Wireless, 802.11 WiFi
LAN, wireless digital cell phone cards, and GPS
nodes.
This note describes one way to interface a
CompactFlash Storage Card to the ADSP-BF535
EZ-KIT Lite™ Evaluation Board. The interface
consists of a hardware and software
implementation, both of which will be discussed
in this application note. In this example, the
interface will demonstrate the playing of MP3
tracks (stored on the CompactFlash card) by the
ADSP-BF535 Blackfin® processor.
configured/formatted by a Windows host PC, it
appears to the host as a standard ATA (IDE) disk
drive.
Figure 1. CompactFlash Storage Card Block
Diagram
Because of this, CompactFlash cards can be
easily interfaced to the ADSP-BF535 Blackfiin
processor’s Asynchronous Memory through the
External Bus Interface Unit (EBIU). The EBIU
provides glueless interfaces to external
memories.
s
Overview
CompactFlash Cards conform to the CF and CF+
standard published by the CompactFlash
Association (CFA). There is an on-card
intelligent controller that manages interface
protocols, data storage and retrieval (see Figure
Figure 2. External Bus Interface Unit (EBIU)
1). Once the CompactFlash card has been
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]
]
]
[1]
]
[0]
[
]
The EBIU is clocked by the system clock
(SCLK) of the ADSP-BF535 Blackfin processor.
On the ADSP-BF535 Blackfin EZ-KIT Lite,
SCLK is set to 120MHz, which will be more
than sufficient for accesses to CompactFlash
cards. Read/Write access times on
CompactFlash cards are defined between 250ns –
300ns (~ 3 – 4 MHz). To find interface/bus
timing, please refer to the CF/CF+ standard
.
CompactFlash cards function in three basic
modes:
• PC Card ATA using Common Memory Mode.
• PC Card ATA using I/O Mode.
• True IDE Mode.
This EE-Note will only deal with 16 bit transfers
using Common Memory Mode.
ADSP-BF535 CompactFlash Interface Pin Mapping
ADSP-BF535
PF8 CD1
AOE OE
AWE
AMS[1
A[11
A[10:2
D[15:0
Vcc
10 kOhm
Address Bus
GND
Data Bus
CompactFlash
WE
CE2
REG
A[10:2]
A
ABE[3] / A[1
A
D
15:0]
CompactFlash Signal Descriptions – Common
Memory Mode
• A[10:1]: Address Lines
• D[15:0]: Data Lines
• /WE (Write Enable): This signal is driven by
the ADSP-BF535 and used for strobing
memory write data to the registers of the
CompactFlash.
• /OE (Output Enable): This strobe is generated
by the ADSP-BF535 and used to read data
from the CompactFlash.
• REG (Attribute Memory Select): This signal
is to distinguish between Common Memory
and Register (Attribute) Memory accesses.
High for Common Memory, Low for Attribute
Memory.
• /CE1, /CE2 (Card Enable): These signals are
used both to select the card and to indicate to
the card whether a byte or a word operation is
being performed. Since both of these signals
are tied to AMS[1] of the ADSP-BF535, we
will be doing word (16-bit) accesses only.
• /CD1 (Card Detect): This signal is used by
the ADSP-BF535 to determine that the
CompactFlash is fully inserted into its socket.
• A[0]: Address line 0 is connected to ground
since this interface supports word accesses
only.
Software Implementation
Since we are using the CompactFlash as a PC
card ATA using memory mode, it will be seen by
the ADSP-BF535 as a standard ATA disk drive.
The following gives a brief explanation of the
file system used on standard disk drives.
Figure 3: CF Interface Pin Mapping
Figure 3 shows the main pin-to-pin connections
between the ADSP-BF535 and the CompactFlash
card.
ADSP-BF535 Blackfin® EZ-KIT Lite™ CompactFlash® Interface (EE-196) Page 2 of 15
FAT file system
Standard disk drives use the FAT (File
Allocation Table) file system. Currently there
are three types of FAT file systems: FAT12,
FAT16, and FAT32. In a FATnn file system, nn
a
represents the size, in bits, of the entries in the
actual FAT structure on the disk. There are 12
bits in a FAT12 FAT entry, 16 bits in a FAT16
FAT entry and 32 bits in a FAT32 FAT entry.
Currently, this interface supports FAT16 only
but other FAT systems could be implemented.
There are 4 basic regions on a FAT volume:
• Reserved Region
• FAT Region
• Root Directory Region (non FAT32)
• File and Directory Data Region
Disk Structure Sector Offset
Boot Sector 0
FAT 1 1
FAT 2 (# of Sectors per FAT) + 1
Name
JumpBoot 3 Jump Instruction to boot
OEMName 8 Name string – MSWIN4.1.
BytesPerSector 2
SectorsPerCluster 1 1, 2, 4, 8, 16, 32, 64, 128.
ReservedSectors 2 1 for FAT12 and FAT16.
FATCount 1 2 FAT data structures.
RootEntCount 2 # of 32-byte entries in root
TotalSectors1 2 Total # of sectors on volume
MediaDescriptor 1 0xF8 for fixed media. 0xF0
SectorsPerFAT 2 # of sectors in one FAT.
SectorsPerTrack 2 Tracks are broken down into
Size
(in
bytes)
Description
code.
, 1024, 2048, 4096.
512
directory.
Bits[15:0].
for removable media.
heads and cylinders.
Root Directory 2*(# of Sectors per FAT)+1
File Clusters (Data
Region)
Table 2. Disk Structure
2*(# of Sectors per FAT)+1+(# of
Root Directory Sectors)
Reserved Region
The Reserved Region contains the Boot Sector
which is the first sector of the volume. A
summary of the FAT16 structure of the Boot
Sector is provide below, starting with the first
word at byte offset 0 (also applies to FAT12):
The Boot Sector contains all the information
about the physical structure of the
CompactFlash. This information is needed to
determine where data is stored on the
CompactFlash for retrieval.
HeadCount 2 Relevant for previous field.
HiddenSectors 4 Count of hidden sectors
preceding FAT volume.
TotalSectors2 4 Total # of sectors on volume
Bits[47:16].
DriveNumber 1 This field is OS specific.
Reserved 1 Reserved.
BootSignature 1 Extended Boot Sig. (0x29).
VolumeID 4 Volume serial number.
VolumeLabel 11 Volume label.
Reserved 8 Reserved.
Table 3. Boot Sector
FAT Region
There are two FAT data structures on the
volume. The reason there are two is to provide
redundancy for the FAT data structure so that if a
sector goes bad in one of the FATs, the data is
not lost because it is duplicated in the other FAT.
Each FAT is a single linked list of the clusters of
a file. These clusters map to the data region of
ADSP-BF535 Blackfin® EZ-KIT Lite™ CompactFlash® Interface (EE-196) Page 3 of 15
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the volume. The first 2 entries in the FAT are
reserved so logical cluster numbers begin at 2.
FAT16 Table
O
f
f
0
1
2
3
4
5
… ………
N-1 0012
N FFFF
Figure 4. FAT File System
Entry
(Next
Cluster)
FFF8
FFFF
0003
0004
000A
0008
(EOF)
Data Region
FAT16 entry values:
• 0x0000: Unused Cluster
• 0xFFF0 – 0xFFF6: Reserved Cluster
Root Directory
The Root Directory is composed of a linear list
of 32-byte structures which represent files stored
on the disk. The following table describes the
different fields of a 32-byte structure within the
Root directory:
Name Size
(in
bytes
)
Name 11 Short name. (see note below)
Attr 1 Bit 0: READ_ONLY
NTRes 1 Reserved for Windows NT use.
CrtTimeTenth 1 File creation time. Millisecond
CrtTime 2 File creation time. 2 second
CrtDate 2 File creation date.
LstAccDate 2 Last read/write date of file.
Description
Bit 1: HIDDEN
Bit 2: SYSTEM
Bit 3: VOLUME_ID
Bit 4: DIRECTORY
Bit 5: ARCHIVE
Bit 6: LONG_NAME
Bits 7 and 8: RESERVED
granularity.
granularity.
• 0xFFF7: Bad Cluster
• 0xFFF8 – 0xFFFF: End of Cluster/File
• Other: Next Cluster in File
The first sector is of cluster 2 and is calculated
as:
FirstDataSector = ReservedSectors + (FATCount *
SectorsPerFAT) + RootDirSectors
FstClusHI 2 File’s first cluster number;
bits[31:16]. This is 0 for
FAT12 and FAT16 volume.
WrtTime 2 Time of last write.
WrtDate 2 Date of last write.
FstClusLO 2 File’s first cluster number;
bits[15:0].
FileSize 4 File size in bytes.
Where
RootDirSectors = ((RootEntCount * 32) + (BytesPerSector
– 1)) / BytesPerSector
The first sector of any cluster N is calculated as:
FirstSectorofCluster = ((N – 2) * SectorsPerCluster) +
FirstDataSector
Table 4. 32-Byte Directory Entry Structure.
Note, if the first byte of the Name field =
• 0xE5: then the entry is free.
• 0x00: then the entry is free; there are no
more allocated entries after this one.
• Values less than 0x20: Not Valid (except
0x05 Å used in Japan).
ADSP-BF535 Blackfin® EZ-KIT Lite™ CompactFlash® Interface (EE-196) Page 4 of 15
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Long file names are not supported in this
software interface.
For FAT32 file systems, the root directory can be
of variable size and is a cluster chain.
For FAT12 and FAT16 file systems, the root
directory immediately follows the last FAT and
has a fixed location and fixed size on the disk.
The first sector of the Root Directory is
computed as:
FirstRootDirSec = ReservedSectors + (FATCount *
SectorsPerFAT)
Blackfin External
Memory Address
0x2400 0800 D[7:0] 0 0 1 0 XX 0 Even RD Data Even WR Data
0x2400 0800 D[15:8] 0 0 1 0 XX 0 Error Feature
0x2400 0802 D[7:0] 0 0 1 0 XX 2 Sector Count Sector Count
0x2400 0802 D[15:8] 0 0 1 0 XX 2 Sector Number Sector Number
0x2400 0804 D[7:0] 0 0 1 0 XX 4 Cylinder Low Cylinder Low
0x2400 0804 D[15:8] 0 0 1 0 XX 4 Cylinder High Cylinder High
0x2400 0806 D[7:0] 0 0 1 0 XX 6 Select Card / Head Select Card / Head
ASM[1]
[ CE2 ] [ CE1 ]
A[11]
A[10] A[9:4]
[ REG ]
Software Accesses to the CompactFlash
In Common Memory Mode, accesses to the
CompactFlash are done through a set of memorymapped registers. The following lists them out
(last two columns of Table 5) as well as the state
of the pins required to access them:
A[3:0]
(HEX)
AOE [ OE ] = 0
ATA Read Register
AWE [ WE ] = 0
ATA Write Register
0x2400 0806 D[15:8] 0 0 1 0 XX 6 Status Command
0x2400 0808 D[7:0] 0 0 1 0 XX 8 Dup. Even RD Data Dup. Even WR Data
0x2400 0808 D[15:8] 0 0 1 0 XX 8 Dup. Odd RD Data Dup. Odd WR Data
0x2400 080C D[15:8] 0 0 1 0 XX C Dup. Error Dup. Features
0x2400 080E D[7:0] 0 0 1 0 XX E Alt. Status Device Control
0x2400 080E D[15:8] 0 0 1 0 XX E Drive Address Reserved
0x2400 0C08 D[7:0] 0 0 1 1 XX 8 Even RD Data Even WR Data
0x2400 0C08 D[15:8] 0 0 1 1 XX 8 Odd RD Data Odd WR Data
Table 5. Memory Mapped Decoding
L PLEASE NOTE – Since we have A[0] tied to ground, we can only do 16-bit accesses to the
CompactFlash with this interface.
Detailed information of these registers can be
found in the CF and CF+ standard
.
The ADSP-BF535 is connected to the CF via
Asynchronous Bank 1 (ASYNC Bank 1) of the
External Bus Interface Unit (EBIU). The starting
location of ASYNC Bank 1 is memory mapped
to address 0x2400 0000 and uses AMS[1] as the
memory bank select line.
From Table 5, we can see that each read/write
access on the ADSP-BF535 will affect two CF
registers. For example, the following piece of
code shows how to set up the Cylinder registers
ADSP-BF535 Blackfin® EZ-KIT Lite™ CompactFlash® Interface (EE-196) Page 5 of 15
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