On Tue, 28 Feb 2006, Lennart Sorensen wrote:
> On Tue, Feb 28, 2006 at 08:10:44AM -0500, linux-os (Dick Johnson) wrote:
>>
>> On Mon, 27 Feb 2006 [email protected] wrote:
>>
>>> On Mon, 27 Feb 2006 22:32:07 +0100, linux-os (Dick Johnson)
>>> <[email protected]> wrote:
>>>
>>>> Flash does not get zeroed to be written! It gets erased, which sets all
>>>> the bits to '1', i.e., all bytes to 0xff.
>>>
>>> Thanks for the correction, but that does not change the discussion.
>>>
>>>> Further, the designers of
>>>> flash disks are not stupid as you assume. The direct access occurs
>>>> to static RAM (read/write stuff).
>>>
>>> I'm not assuming anything . Some hardware has been killed by this issue.
>>> http://lkml.org/lkml/2005/5/13/144
>>
>> No. That hardware was not killed by that issue. The writer, or another
>> who had encountered the same issue, eventually repartitioned and
>> reformatted the device. The partition table had gotten corrupted by
>> some experiments and the writer assumed that the device was broken.
>> It wasn't.
>>
>> Also, if you read other elements in this thread, you would have
>> learned about something that has become somewhat of a red herring.
>>
>> It takes about a second to erase a 64k physical sector. This is
>> a required operation before it is written. Since the projected
>> life of these new devices is about 5 to 10 million such cycles,
>> (older NAND flash used in modems was only 100-200k) the writer
>> would have to be running that "brand new device" for at least
>> 5 million seconds. Let's see:
>
> How come I can write to my compact flash at about 2M/s if you claim it
> takes 1s to erase a 64k sector? Somehow I think your number is much too
> high. Or it can do multiple erases at the same time.
>
> Also the 5 to 10 million is a lot higher than the numbers the makers of
> the compact flash cards I use claim.
>
Here is an instrumented erase function on a driver that rewrites
the first sector of a BIOS ROM. Unlike the Flash DISKS, the
BIOS ROM has no buffering in static RAM so you can gustimate
the actual time to erase............
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
//
// This erases a page and waits for the erasure to complete. It
// returns false if it failed.
//
static int erase(void *bios, int page)
{
int era;
flags_t flags;
jiffie_t ticks, start;
spin_lock_irqsave(&info->lock, flags);
erase_page(bios, page);
spin_unlock_irqrestore(&info->lock, flags);
start = jiffies;
ticks = jiffies + (ERA_TIME * HZ);
era = 0x00;
while(time_before(jiffies, ticks))
{
if((era = check_erase(bios, page)))
break;
if(signal_pending(current))
break;
set_current_state(TASK_INTERRUPTIBLE);
schedule_timeout(1);
}
set_current_state(TASK_RUNNING);
printk("They don't believe... %d\n", (int) (jiffies - start));
return era;
}
[SNIPPED...]
On the system I rewrite a BIOS sector on, jiffies is 1024 ticks/second.
parport: PnPBIOS parport detected.
parport0: PC-style at 0x378, irq 7 [PCSPP,TRISTATE]
lp0: using parport0 (interrupt-driven).
lp0: console ready
device eth0 entered promiscuous mode
device eth0 left promiscuous mode
device eth0 entered promiscuous mode
device eth0 left promiscuous mode
Analogic-BiosDev : Initialization complete
They don't believe... 1004
Now, the wait for erase always sleeps for at least a timer-tick
(about a milisecond) so this may take longer than the physical
erase, but not much longer.
The erase function is:
#-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
#
# This erases the NVRAM page (block). It doesn't wait for completion.
# Each block is 64k in length.
# M29W040B chip
#
.section .text
erase_page:
pushl %ebx
movl BUF(%esp), %ebx # Address of the chip
movl DAT(%esp), %ecx # The page
andl $0x07, %ecx # Max pages
shll $0x10, %ecx # Times 64k
movb $0xf0, (%ebx) # Reset
movb $0xaa, 0x555(%ebx)
movb $0x55, 0x2aa(%ebx)
movb $0x80, 0x555(%ebx)
movb $0xaa, 0x555(%ebx)
movb $0x55, 0x2aa(%ebx)
movb $0x30, (%ecx,%ebx)
popl %ebx
ret
.size erase_page,.-erase_page
.type erase_page,@function
.global erase_page
And the check-erase function is this:
#-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
#
# This reads the whole M29W040B page, looking for all 0xffff words.
# It returns non-zero if it has been erased and zero otherwise.
#
check_erase:
pushl %edi
movl BUF(%esp), %edi # Point to buffer
movl DAT(%esp), %eax # 64k page
andl $0x07, %eax # Max pages possible
shll $0x10, %eax # Times 64k
addl %eax, %edi # Offset to start
cld
movl $0x8000, %ecx # Number of words to check
movl $-1, %eax # What to look for
repz scasw # Look for all 0xffff
jz 1f # All erased
incl %eax # -1 becomes zero
1: popl %edi
ret
.size check_erase,.-check_erase
.type check_erase,@function
.global check_erase
>> 60 seconds per minute
>> 3600 seconds per hour
>> 86400 seconds per day.
>>
>> 5,000,000 / 86400 = 57 days of continuous writes to the same
>> sector. The writer surely would have a strange file because
>> he states that even a single large file can destroy the drive
>> if it is mounted with the "sync" option.
>>
>> Also, the failure mode of NAND flash is not that it becomes
>> "destroyed". The failure mode is a slow loss of data. The
>> devices no longer retain data for a zillion years, only a
>> few hundred, eventually, only a year or so. So when somebody
>> claims that the flash has gotten destroyed, they need to have
>> written it for a few months, then waited for a few years before
>> reporting the event.
>
> Some flash devices can be "destroyed" by loosing power in the middle of
> a write, since this causes them to corrupt their table of blocks and
> only the manufacturer has the ability to reset that. Fortunately this
> doesn't seem like too common a design.
>
# dd if=/dev/zero of=/dev/whatever bs=1M count=128
Fixes a 128 megabyte flash disk, plug in other values for other
sizes.
> Len Sorensen
Cheers,
Dick Johnson
Penguin : Linux version 2.6.15.4 on an i686 machine (5589.54 BogoMips).
Warning : 98.36% of all statistics are fiction, book release in April.
_
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