Samsung V1.3.0, Porting Manual

4. Writing the sector data to the modified page 

These sequences of operations are not atomic, so a write request to this block device driver 
is prone to data corruption. For this reason, read-only file systems such as CRAMFS are 

adequate to run on top of this block device driver. 
 

•

 STL Block Device Driver: This block device driver is used to provide driver functions for 

the device files /dev/stl0/*, /dev/stl1/* and so on. Since there is FTL between this block 

device driver and BML, it is allowed to perform random write requests and write requests 
are handled atomically. Thus any read-write file system (e.g. RFS) can run on this block 

device driver. 
 

 XSR core 

XSR core is composed of two layers: STL (Sector Translation Layer) and BML (Block Management 

Layer). STL is a top layer of XSR. BML is below the STL. These layers have different features 
and jointly provide block device interface to upper layer. The main features of each layer are 

as follows.  
 

•

 STL (Sector Translation Layer): translates a logical address from the file system into the 

virtual flash address. It internally has wear-leveling

1

 during the address translation.   

•

 BML (Block Management Layer): translates the virtual address from the upper layer into 

the physical address. At this time, BML does the address translation in consideration of bad 
block and the number of NAND device in use. BML accesses LLD

2

, which actually performs 

read, write, or erase operation, with the physical address. 

☞

 Note 

Each layer of XSR can be operated separately as a module. Thus, STL can be used with 
other layer, which has same functionalities with BML.                                                                                 

 OAM (OS Adaptation Module) 

OAM is at the right of the figure. OAM connects XSR with the OS. OAM needs to be configured 
according to your OS environment to use NAND flash memory. OAM module is already 

configured with RFS for Linux. 

 PAM (Platform Adaptation Module) 

PAM is below OAM. PAM connects XSR with the platform. PAM also needs to be configured 

according to your platform to use NAND flash memory. 

 LLD (Low Level Driver) 

There is a low level device driver between BML and NAND flash memory. It reads, writes, or 

erases data on the physical sector address received from XSR and is controlled by BML. 
 

„

1

 Wear-leveling is an internal operation to use every block of NAND flash memory evenly through the 

algorithm. It extends NAND flash memory life span. 

„

2

 LLD is an abbreviation of Low Level Device Driver. It performs actual read/write/erase operation to 

NAND flash memory as a device driver. 

3         

Linux 

RFS 

v1.3.0 

Porting 

Guide