Samsung S5PC110, Manual

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S5PC110_UM 4 NAND FLASH CONTROLLER
4-13
4.3.12 LOCK SCHEME FOR DATA PROTECTION
NFCON provides a lock scheme to protect data stored in external NAND Flash memories from malicious program.
For this scheme, the NFSBLK and NFEBLK registers are used to provide access control methods; only the
memory area between NFSBLK and NFEBLK is erasable and programmable, but the read access is available to
whole memory area.
This lock scheme is only available when you enable LockTight(NFCONT[17]) and LOCK(NFCONT[16]).
1. Unlock mode
In unlock mode, user can access whole NAND memory; there are no constraints to access memory.
2. Soft lock mode
In soft lock mode, you can access NAND block area between NFSBLK and NFEBLK.
When you try to program or erase the locked area, an illegal access error will occur (NFSTAT [5] bit will be
set).
3. Lock-tight mode
In lock-tight mode, you can access NAND block area between NFSBLK and NFEBLK as soft lock mode. The
differences is that you cannot change NFSBLK and NFEBLK registers, and also LOCK(NFCONT[16]) and
LockTight(NFCONT[17]) bits.
When you try to program or erase the locked area, an illegal access error will occur (NFSTAT[5] bit will be set).
The LockTight(NFCONT[17]) bit is only cleared when reset or wake up from sleep mode (It is impossible to clear it
by software).
The accessibility of NAND area is illustrated in the figure below.
when Lock-tight =1
or SoftLock=1
NAND flash memory
Locked area
(Read only)
Prorammable/
Readable
Area
Locked area
(Read only)
Address
High
Low
1
NFEBLK
NFSBLK
NFEBLK Locked Area
(Read only)
When NFSBLK=NFEBLK
NFSBLK
NFSBLK - 1
NOTE:
If the address of NFSBLK and NFEBLK are same, then the erase and program to all NAND memory are not allowed.