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| 型號(hào)： | 22374A |
| 英文描述： | Migrating between Boot and Uniform Sectored Flash Devices |
| 中文描述： | 引導(dǎo)和之間的遷移統(tǒng)一扇區(qū)閃存器件 |
| 文件頁(yè)數(shù)： | 4/5頁(yè) |
| 文件大?。?/td> | 78K |
| 代理商： | 22374A |
Migrating Between Boot and Uniform Sectored Flash Devices
3
Case 2
The system requires an erase to one or more of the
boot blocks, but data in the other boot blocks need to
be preserved.
Solution
You will need to change some address pointers for the
smaller boot blocks. To determine if the code currently
in the boot sectors needs to be placed in its own indi-
vidual 64 Kbyte sector, the question you need to ask is:
Does the code need to be modified by itself or can it be
updated at the same time as other parts of the code
If it can be modified with other portions of the code,
then you can group portions of the code together to po-
tentially occupy all or part of a single 64 Kbyte sector.
If it absolutely needs to be changed by itself then you
must place it in its own 64 Kbyte sector. For each ad-
ditional sector required you need to change the
address pointers. Let’s look at an example:
In this case, let’s assume that you are migrating from a
32 Mb boot block device to a 64 Mb uniform device.
The first two 8K bytes sectors are the boot code, which
is never changed, and the other 8 Kbyte boot sectors
are used to store the operating code, which may need
to be upgraded later. The boot code must be loaded
into it’s own 64 Kbyte sector and the addressing does
not change. The rest of the boot sectors need to be
placed in a one of the new 64 Kbyte sectors available
in the larger memory device and the address pointers
updated. Also please note that when migrating from
boot to uniform it may be necessary to leave a small
amount of memory space unused (48 Kbyte in the last
figure) in order to retain the flexibility of the older boot
sectored device.
Software Changes When Migrating From
Uniform To Boot
Case 1
The system does not need to take advantage of the
smaller boot sectors.
Solution
A small software change is needed to tell flash device
to erase all of the smaller sectors at once. This can be
done by adding the sector addresses to the end of the
normal sector erase command. Looking at an example
going from uniform to bottom boot, the original sector
erase command for a uniform sectored device would
look like this:
Where SA0 is any address within the first 64 Kbyte sec-
tor. In order to convert to a bottom boot device you
need to modify the sector erase command to look like
this:
Now SA0 points to any address within the first
16 Kbytes, SA1 points to an address within the next
8 Kbytes, SA2 points to the next 8 Kbytes after that,
and finally SA3 points to the last 32 Kbytes. Together
the sector erases cover the first 64 Kbytes of the de-
vice. So this command will erase all of the small boot
sectors at once, effectively making it one large uniform
sector. All other sector erase commands will remain
the same since the devices are identical past the first
64 Kbytes.
Case 2
The system will be taking advantage of the flexibility of-
fered by the smaller boot sectors by erasing them
separately of one another.
Solution
Software changes will be necessary, but only to control
erasing of the smaller sectors. Erasing of other sec-
tors, programming, and reading the flash device
remain the same. For each sector to be erased sepa-
rately you need to include the following command
sequence to specify it independent of the other sectors
as well as identifying when the command will be called
in the code.
8 Kbyte Sector
8 Kbyte Sector
8 Kbyte Sector
8 Kbyte Sector
8 Kbyte Sector
8 Kbyte Sector
8 Kbyte Sector
8 Kbyte Sector
8 Kbyte Sector
8 Kbyte Sector
8 Kbyte Sector
8 Kbyte Sector
8 Kbyte Sector
8 Kbyte Sector
8 Kbyte Sector
8 Kbyte Sector
16 Kbytes
Available
64 Kbyte Sector
48 Kbytes
Not Used
Am29LV320B
Am29LV640U
Address
555
2AA
555
555
2AA
SA0
Data
AA
55
80
AA
55
30
Address 555 2AA 555
555 2AA SA0 SA1 SA2 SA3
Data
AA
55
80
AA
55
30
30
30
30
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