NOR Flash Driver
15-2 DRIVER & DEVICE CHARACTERISTICS
NOR devices, no matter what attachment interface (serial or parallel), share certain
characteristics. The medium is always organized into units (called blocks) which are erased
at the same time; when erased, all bits are 1. Only an erase operation can change a bit from
a 0 to a 1, but any bit can be individually programmed from a 1 to a 0. The μC/FS driver
requires that any 2-byte word can be individually accessed (read or programmed).
The driver RAM requirement depends on flash parameters such as block size and run-time
configurations such as sector size. For a particular instance, a general formula can give an
approximate:
if (secs_per_blk < 255) {
temp1 = ceil(blk_cnt_used / 8) + (blk_cnt_used * 1);
} else {
temp1 = ceil(blk_cnt_used / 8) + (blk_cnt_used * 2);
}
if (sec_cnt < 65535) {
temp2 = sec_cnt * 2;
} else {
temp2 = sec_cnt * 4;
}
temp3 = sec_size;
TOTAL = temp1 + temp2 + temp3;
where
secs_per_blk
The number of sectors per block.
blk_cnt_used
The number of blocks on the flash which will be used for the file
system.
sec_cnt
The total number of sectors on the device.
sec_size
The sector size configured for the device, in octets.
154
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