Secure Read Protection - STMicroelectronics SPC572L series Reference Manual

Flash Memory Programming and Configuration
Start Address End Address
0x00FC_C000 0x00FC_FFFF
0x0060_C000 0x0060_FFFF
31.4

Secure read protection

Read Protection is ability of the flash controller to block read accesses to the flash memory
from all bus masters. This includes the blocking of:
• Instruction fetches and load instructions from the CPU
•
Debug reads from an outside tool
• DMA reads
•
SIPI reads
• All other types of bus master reads
When secure read protection is active, the affected flash blocks are readable by any bus
master until a debugger is attached to the JTAG port and debug is enabled. If a debugger is
attached and debug is enabled while an application is running, the next access to a flash
read protected region terminates with a bus error.
Most instances of flash memory read protection in the SPC572Lx microcontroller are not
configurable by the customer. An example of this is the 256-bit passwords stored in UTEST
flash memory. Password-based read protection is customer-configurable
the password-based write protection mechanism detailed in
protection.
There are two significant differences between password-based read protection and
password-based write protection in the SPC572Lx microcontroller.
1. Read protection can only be applied to pre-defined groups of flash memory blocks.
These groups, called "Read Lock groups", cannot be re-defined, meaning the blocks
assigned to those groups are permanently assigned and cannot be assigned to other
groups and no new groups can be created.
2. Read protection is only active either when a debugger is attached to the JTAG port and
debug is enabled; or the lifecycle has been advanced to "Failure Analysis".
j. Secure read protection is user-configurable in that the default lock/unlock state for each mapped block at reset
is controlled by user-created DCF records, giving the user the ability to determine the number of levels of
password protection implemented. The read protection is applied to groups of blocks instead of individual
blocks and the groups are not user-definable.
666/2058
Size LOCKn
Register Field
(KB) Register
16 1 LOCK0 LOWLOCK[4]
16 1 LOCK0 LOWLOCK[5]
DocID027809 Rev 4
LOCKn
LOCKn DCF
Record
Bit DATA group
Bit
20
21
Section 31.3: Secure write
RM0400
Read
Bloc
Lock Description
k No.
1 4 Code Flash
3 5 Secure Code
(j)
and is similar to
4