Purging - FIGnition FUZE Hardware Reference Manual

Therefore can always create the table of Virtual blocks numbers just by knowing what or-
der they used physical blocks [Fig 5.8].
This technique works, because the only thing we need to do every time we need a new
physical block is store the new virtual block number that uses it at the end of the list and
that means we don't need to overwrite cells within the virtual block number table.
In practice the FIGnition Virtual block driver uses the first two sectors of Flash storage to
store the inverse Virtual block number table and it uses the Flash after the first 32Kb for
the actual physical pages.
This technique has one major disadvantage, because as the list grows longer and longer,
it takes longer to look up virtual blocks.

5.3.2 Purging

Virtual block numbering allows us to treat flash storage as a disk, but eventually all the
available physical blocks will be used up. If we could figure out which physical blocks re-
place older physical blocks with the same virtual page number, then perhaps we could
erase those blocks and re-use them. This is called purging [Fig 5.10].
Fig 5.8
Fig 5.9