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SAMA5 NAND: Updated README and configuration logic

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This commit is contained in:
Gregory Nutt 2013-12-03 14:32:59 -06:00
parent e90d6cf262
commit 80841d135d
3 changed files with 115 additions and 38 deletions
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5
configs/sama5d3x-ek/Kconfig
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@ -56,6 +56,8 @@ choice
config SAMA5_NAND_FTL
bool "Create NAND FLASH block driver"
default n
depends on MTD && MTD_NAND
---help---
Create the MTD driver for the NAND and "wrap" the NAND as a standard
block driver that could then, for example, be mounted using FAT or
@ -69,7 +71,8 @@ config SAMA5_NAND_FTL
config SAMA5_NAND_NXFFS
bool "Create NAND FLASH NXFFS file system"
depends on FS_NXFFS
default n
depends on MTD && MTD_NAND && FS_NXFFS && NXFFS_NAND
---help---
Create the MTD driver for the NAND and mount the NAND device as
a wear-leveling, NuttX FLASH file system (NXFFS). The downside of

132
configs/sama5d3x-ek/README.txt
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@ -1428,42 +1428,17 @@ NAND Support
Other file systems are not recommended because only NXFFS can handle
bad blocks and only NXFFS performs wear-leveling.
NOTE: NXFFS can be very slow. The first time that you start the
system, be prepared for a wait; NXFFS will need to format the NAND
volume. I have lots of debug on so I don't yet know what the
optimized wait will be. But with debug ON, software ECC, and no
DMA the wait is in many tens of minutes (and substantially longer
if many debug options are enabled.
[I don't yet have data for the more optimal cases. It will be
significantly less, but still not fast.]
On subsequent boots, after the NXFFS file system has been created the
delay will be less. When the new file system is empty, it will be
very fast. But the NAND-related boot time can become substantial when
there has been a lot of usage of the NAND. This is because NXFFS
needs to scan the NAND device and build the in-memory dataset needed
to access NAND and there is more that must be scanned after the device
has been used. You may want tocreate a separate thread at boot time
to bring up NXFFS so that you don't delay the boot-to-prompt time
excessively in these longer delay cases.
NOTE: There is another NXFFS related issue: When the FLASH is
fully used, NXFFS will restructure the entire FLASH, the delay to
restructure the entire FLASH will probably be even larger. This
solution in this case is to implement an NXFSS clean-up daemon that
does the job a little-at-a-time so that there is no massive clean-up
when the FLASH becomes full.
FAT
---
Another option is FAT. FAT, however, will not handle bad blocks and
does not perform any wear leveling.
File Systems:
CONFIG_FS_NXFFS=y : Enable the NXFFS file system
CONFIG_FS_FAT=y : Enable the FAT FS
CONFIG_FAT_LCNAMES=y : With lower case name support
CONFIG_FAT_LFN=y : And (patented) FAT long file name support
CONFIG_FS_NXFFS=n : Don't need NXFFS
Defaults for all other NXFFS settings should be okay.
@ -1507,27 +1482,111 @@ NAND Support
nsh> mount
/mnt/mystuff type nxffs
NOTES:
1. NXFFS can be very slow. The first time that you start the system,
be prepared for a wait; NXFFS will need to format the NAND volume.
I have lots of debug on so I don't yet know what the optimized wait
will be. But with debug ON, software ECC, and no DMA the wait is
in many tens of minutes (and substantially longer if many debug
options are enabled.
[I don't yet have data for the more optimal cases. It will be
significantly less, but still not fast.]
2. On subsequent boots, after the NXFFS file system has been created
the delay will be less. When the new file system is empty, it will
be very fast. But the NAND-related boot time can become substantial
whenthere has been a lot of usage of the NAND. This is because
NXFFS needs to scan the NAND device and build the in-memory dataset
needed to access NAND and there is more that must be scanned after
the device has been used. You may want tocreate a separate thread at
boot time to bring up NXFFS so that you don't delay the boot-to-prompt
time excessively in these longer delay cases.
3. There is another NXFFS related performance issue: When the FLASH
is fully used, NXFFS will restructure the entire FLASH, the delay
to restructure the entire FLASH will probably be even larger. This
solution in this case is to implement an NXFSS clean-up daemon that
does the job a little-at-a-time so that there is no massive clean-up
when the FLASH becomes full.
4. Bad NXFFS behavior with NAND: If you restart NuttX, the files that
you wrote to NAND will be gone. Why? Because the multiple writes
have corrupted the NAND ECC bits. See STATUS below. NXFFS would
require a major overhaul to be usable with NAND.
Using NAND with FAT
-------------------
[Unverified]
If configured for FAT, the system will create block driver at
/dev/mtdblock0. The NSH mkfatfs command can be used to format a FAT
file system on NAND.
/dev/mtdblock0:
NuttShell (NSH)
nsh> ls /dev
/dev:
console
mtdblock0
null
ttyS0
You will not that the system comes up immediately because there is not
need to scan the volume in this case..
The NSH 'mkfatfs' command can be used to format a FATfile system on
NAND.
nsh> mkfatfs /dev/mtdblock0
This step, on the other hand, requires quite a bit of time.
And the FAT file system can be mounted like:
nsh> mount -t vfat /dev/mtdblock0 /mnt/nand
nsh> ls /mnt/nand
/mnt/nand:
nsh> echo "This is a test" > /mnt/nand/atest.txt
NOTE: This will take a long time because it will require reading,
modifying, and re-writting the 128KB erase page!
nsh> ls -l /mnt/nand
/mnt/nand:
-rw-rw-rw- 16 atest.txt
nsh> cat /mnt/fat/atest.txt
This is a test
NOTES:
1. Unlike NXFFS, FAT can work with NAND. But there are some
signifcant issues.
2. First, each NAND write access will cause a 256KB data transefer: It
will read the entire 128KB erase block, modify it and write it back
to memory. There is some caching logic so that this cached erase
block can be re-used if possible and writes will be deferred as long
as possible.
3. If you hit a bad block, then FAT is finished. There is no mechanism
in place in FAT not to mark and skip over bad blocks.
What is Needed
--------------
What is needed to work with FAT properly would be another MTD layer
between the FTL layer and the NAND FLASH layer. That layer would
perform bad block detection and sparing so that FAT works transparently
on top of the NAND.
Another, less general option would be support bad blocks within FAT.
STATUS
------
1. PMECC has not been test and is, most likely, non-functional.
1. PMECC has not been tested and is, most likely, non-functional.
2. DMA works (with software ECC), but is see occasional wild memory
2. DMA works (with software ECC), but I see occasional wild memory
clobbering. DMA should not be used until this problem can be
worked out.
@ -1554,6 +1613,9 @@ NAND Support
This may prohibit NXFFS from ever being used with NAND.
4. As mentioned above, FAT does work but (1) has some performance issues on
writes and (2) cannot handle bad blocks.
AT24 Serial EEPROM
==================

16
configs/sama5d3x-ek/src/sama5d3x-ek.h
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@ -100,11 +100,23 @@
# undef HAVE_NAND
#endif
/* Can't support NAND if the MTD feature is not enabled */
#if !defined(CONFIG_MTD) || !defined(CONFIG_MTD_NAND)
# undef HAVE_NAND
#endif
/* If we are going to mount the NAND, then they user must also have told
* us what to do with it by setting one of these.
* us what to do with it by setting one of CONFIG_SAMA5_NAND_FTL or
* CONFIG_SAMA5_NAND_NXFFS.
*/
#ifndef CONFIG_FS_NXFFS
#ifndef CONFIG_MTD
# undef CONFIG_SAMA5_NAND_NXFFS
# undef CONFIG_SAMA5_NAND_FTL
#endif
#if !defined(CONFIG_FS_NXFFS) || !defined(CONFIG_NXFFS_NAND)
# undef CONFIG_SAMA5_NAND_NXFFS
#endif