NOR Flash Driver
secs_per_blk and sec_cnt can be calculated from more basic parameters:
secs_per_blk = floor(blk_size / sec_size);
sec_cnt = secs_per_blk * blk_cnt_used;
where
blk_size
The size of a block on the device, in octets
Take as an example a 16-Mb NOR that is entirely dedicated to file system usage, with a
64-KB block size, configured with a 512-B sector. The following parameters describe the
format:
blk_cnt_used
blk_size
sec_size
secs_per_blk
sec_cnt
=
=
=
=
=
32;
65536;
512;
65536 / 512 = 128;
128 * 32 = 4096;
and the RAM usage is approximately
temp1
temp2
temp3
TOTAL
=
=
=
=
(32 / 8) + (32 * 2) = 68;
4096 * 2 = 8192;
512;
68 + 8192 + 512 = 8772;
In this example, as in most situations, increasing the sector size will decrease the RAM
usage. If the sector size were 1024-B, only 5188-B would have been needed, but a moderate
performance penalty would be paid.
155
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